Continuing Education Activity

Gout is one of the most prevalent causes of chronic inflammatory arthritis in the United States, characterized by the deposition of monosodium urate (MSU) monohydrate crystals in tissues. This activity explores the etiology, pathophysiology, and management of gout, with particular attention to current guideline-based treatment strategies. Emphasis is placed on urate-lowering therapies and prophylactic measures to prevent recurrent flares and long-term complications. This continuing education activity is designed to enhance clinicians' understanding of evidence-based gout management, enabling healthcare professionals to improve diagnostic accuracy, optimize treatment selection, and reduce disease burden through effective long-term care. 

Objectives:

• Identify the clinical and biochemical markers of gout, including serum urate levels, monosodium urate crystals in synovial fluid and formulate an accurate diagnosis.
• Screen for gout risk factors, hyperuricemia, and associated comorbidities, especially in at-risk patients.
• Implement appropriate urate-lowering therapies for acute flare and prophylaxis of gout according to American College of Rheumatology guidelines. 
• Collaborate with healthcare providers to facilitate comprehensive care, ensuring consistent messaging and therapy coordination.

Introduction

Gout was historically called the "disease of kings" because it was prevalent among the wealthy. Today, it is one of the most common causes of inflammatory arthritis in the United States, affecting around 5.9% of men and 2% of women.[1] The term "gout" is derived from the Latin "gutta," meaning "drop," reflecting the medieval belief that the condition resulted from a drop of "evil humors." Early descriptions date back to ancient times, with Hippocrates recognizing podagra and ancient Egyptian texts also documenting the disease. 

Gout is defined by the deposition of monosodium urate (MSU) monohydrate crystals in joints and periarticular tissues (see Image. Monosodium Urate Crystals and Acute Gouty Inflammation).[2][3] It is one of the most studied and clinically manageable rheumatic diseases.[4][5] Gout is usually preceded by hyperuricemia, defined as a plasma or serum urate concentration exceeding 6.8 mg/dL (approximately 400 µmol/L), which is the solubility threshold for urate in blood.[6] 

Clinical manifestations of gout include acute gouty arthritis, tophaceous gout caused by MSU crystal deposits in articular, cartilaginous, and soft tissues, uric acid nephrolithiasis, and chronic nephropathy. These manifestations may occur intermittently or progress to chronic disease with recurrent flares and persistent joint damage if left untreated.

Etiology

Gout results from sustained hyperuricemia with subsequent MSU crystal deposition in joints and periarticular tissues. The etiology is multifactorial, involving genetic predisposition, comorbidities, and dietary and environmental factors. Rare single-gene enzyme defects cause early-onset or severe disease. Regardless of the trigger, the final common pathway is urate supersaturation, which promotes MSU crystallization and triggers inflammation.

Genetic Factors

Heritability of serum urate is approximatley 70%, and 40% to 50% of patients report a positive family history.[7] Most risk alleles influence renal and intestinal urate transport or purine metabolism. Genetic factors associated with gout can be grouped into 4 major categories [7][8]

• Renal tubular reabsorption: SLC22A12 (URAT1), SLC2A9 (GLUT9)
• Excretion (renal/intestinal): ABCG2, SLC17A1–A3, ABCC4, SLC22A6, SLC22A8
• Purine production: HPRT1, PRPS1, ALDH16A1 (rare, high-penetrance)
• Regulatory/other: PDZK1, GCKR, UMOD, SLC16A9, PKD2, ALDH2, SCGN  

Evolutionary and Physiologic Context

The final stage of purine metabolism involves the sequential conversion of hypoxanthine to xanthine, and then of xanthine to uric acid, by xanthine oxidase. In most mammals, uric acid is further metabolized to the more soluble allantoin by uricase. Humans, higher primates, giraffes, and Dalmatians lack functional uricase due to a gene inactivation event about 25 million years ago.[9][10] At the same time, increased URAT1 activity and loss of endogenous vitamin C synthesis (~20 million years ago) led to higher baseline urate levels, giving rise to the “antioxidant replacement theory,” in which uric acid partly substituted for ascorbic acid.[10]

Consequently, humans are uniquely susceptible to spontaneous hyperuricemia and gout.[2][10] This evolutionary loss of uricase contributes to higher baseline serum urate levels compared with most other mammals.

Hyperuricemia and Absolute Risk

Gout risk increases monotonically with serum urate level. Concentrations above 9 mg/dL are associated with a 3 times greater likelihood of a flare within 1 year compared with levels below 6 mg/dL (see Table. Incident Gout by Baseline Serum Uric Acid)

Table

Table 1. Incident Gout by Baseline Serum Uric Acid (mg/dL) [11].

Clinical takeaway: Risk steepens markedly once SUA ≥8 mg/dL and is high at ≥9 mg/dL.

Secondary Causes and Modifiable Risks

Any condition that alters extracellular urate concentration can trigger a gout flare-up. These conditions include various factors such as stress (mainly due to medical illnesses like cardiovascular illnesses, recent surgical procedure, trauma, dehydration, or starvation), dietary choices (such as the consumption of high-purine foods like organ meats or seafood, as well as alcoholic beverages like beer, wine, and spirits), and drugs (including aspirin, diuretics, or even allopurinol).

Epidemiological studies have reported a rising burden of gout, primarily attributed to lifestyle changes like increased protein consumption and a sedentary lifestyle. These shifts in habits highlight the complex relationship between modern lifestyle patterns and the prevalence of gout in contemporary society.

Additional factors linked to gout and hyperuricemia include older age, male sex, obesity, a purine-rich diet, alcohol, certain medications, comorbid diseases, and genetic predisposition (see Table. Causes of Hyperuricemia). Medications such as diuretics, low-dose aspirin, ethambutol, pyrazinamide, and cyclosporine have been identified as potential contributors to elevated uric acid levels and gout development.  

Hyperuricemia reflects overproduction (↑purine turnover) and/or underexcretion (renal). Frequent contributors are the following[2][12][13]:

• Comorbidities: Chronic kidney disease (CKD), hypertension, obesity, metabolic syndrome, diabetes, hyperlipidemia
• Medications raising urate: Thiazide/loop diuretics, low-dose aspirin, cyclosporine, tacrolimus, pyrazinamide, ethambutol
• Dietary/exogenous: Alcohol (beer > spirits > wine), red/organ meats, shellfish, fructose-sweetened beverages

Table

Table 2. Risk Factors of Hyperuricemia and Gout [2][9][14].

Table

Table 3. Causes of Hyperuricemia.

Clinical pearl: In adults, underexcretion is far more common than pure overproduction.

Dietary Factors That May Lower Serum Uric Acid

Certain dietary practices have been shown to lower serum uric acid and reduce the risk of incident gout. Higher consumption of meat and seafood is associated with an increased incidence of gout in men. Conversely, increased dairy intake is associated with a lower incidence of gout in men.[15] Additionally, following the Dietary Approaches to Stop Hypertension (DASH) diet has been shown to lower serum uric acid levels and reduce the risk of gout.[16][17] Adequate vitamin C intake is associated with decreased serum uric acid and a reduced risk of gout.[18][19][20][21][22] Furthermore, incorporating cherries into the diet has been shown to decrease serum uric acid [23] and reduce the risk of recurrent gout attacks.[16][24]

Obstructive Sleep Apnea and Uric Acid

Intermittent hypoxia increases purine degradation and reduces renal urate clearance, raising serum uric acid levels. Associations with clinical gout are modest and are substantially attenuated after adjusting for confounders such as body mass index and type 2 diabetes mellitus. Obstructive sleep apnea (OSA) should be managed on its own merits and not considered a primary cause of gout.[25][26][27] Randomized studies suggest that OSA is causally associated with elevated serum uric acid but is not independently associated with gout after accounting for shared risk factors.[28]

Epidemiology

Epidemiological estimates depend on the definition of the disease. A definitive diagnosis of gout is accepted in the presence of MSU monohydrate crystals in the joint fluid or the identification of tophus. However, given the impracticality of identifying gout through these criteria alone, various case definitions have been devised, including self-reports, the Rome criteria, the New York criteria, the American College of Rheumatology (ACR) criteria, and the 2015 ACR/European League Against Rheumatism (EULAR) criteria. The 2015 ACR/EULAR criteria have a sensitivity of 92% and a specificity of 89%, surpassing the accuracy of all previous definitions and enabling more precise and reliable diagnosis of gout in epidemiological studies. 

In men, serum urate typically ranges from 5 to 6 mg/dL and is usually attained during puberty, with a slight increase with age alone.[29] Conversely, women exhibit lower serum urate concentrations, averaging 1.0 to 1.5 mg/dL, compared with men of the same age, a difference likely attributable to estrogen-mediated renal uric acid clearance.[30][31] Following menopause, urate concentrations in women rise to levels comparable to those in adult men.[30] Gender-based variation in urate concentration contributes to clinical differences between women and men at the onset of gout.[31][32]

The prevalence of gout can vary by age, sex, and country of origin. Older age and male sex are 2 common risk factors recognized globally. In Western nations, the prevalence of gout is significantly higher in men (3%-6%) compared to women (1%-2%), with a notable 2- to 6-fold difference. The prevalence of gout rises with age but plateaus after 70 years (see Table. Prevalence by Age Range).

Data from 2007 to 2008 showed that about 3.9% of US adults were diagnosed with gout.[33] Estimates of gout prevalence in the United States range from fewer than 3 million to more than 8 million individuals. The latest estimates suggest a gout prevalence of over 3% among adults in the United States.[1][34][35] 

Additionally, data based on the National Health and Nutrition Examination Survey (NHANES)  from 2007 to 2016 indicate a higher prevalence of gout in African-American individuals than in White individuals in the USA. Among females, gout prevalence is 3.5% in African Americans and 2.0% in White Americans, with an odds ratio (OR) of 1.81. Among males, the prevalence in African Americans is 7.0% and 5.4% in White Americans, with an OR of 1.26. Hyperuricemia was also more prevalent in African American females and males than their White counterparts, with ORs of 2.00 and 1.39, respectively.[36]  

Table

Table 4. Prevalence by Age Range .

The incidence of gout has increased over the past several decades, with higher rates in men than women and rising with age. A study conducted in Olmsted County, MN, from 1989 to 2009 revealed an increase in gout incidence and comorbidities over the 20 years.[37] Similarly, in the United Kingdom, the prevalence of gout increased from 1.52% to 2.49% between 1997 and 2012.[38]

Comorbidities

Gout is associated with health risks, including obesity, hypertension, CKD, diabetes mellitus, hyperlipidemia, and metabolic syndrome. A study conducted in Olmsted County, MN, reported a higher prevalence of comorbidities among patients with gout than in the general population. The prevalence of obesity (defined as body mass index [BMI] >35 kg/m2) was 29% in gout patients versus 10% in the general population, hypertension was 69% versus 54%, CKD was 28% versus 11%, diabetes mellitus was 25% versus 6%, and hyperlipidemia was 61% versus 21%.[37] 

Adult weight gain is consistently associated with an increased risk of gout.[39][40][41] Studies from the United Kingdom and Germany have revealed associations between gout and various comorbidities, including diabetes mellitus, congestive heart failure (CHF), hypertension, myocardial infarction (MI), and obesity. Additionally, the prevalence of comorbidities increased with higher serum uric acid levels.[42] 

Other gout-related comorbidities include hyperlipidemia, hypothyroidism, anemia, psoriasis, chronic pulmonary disease, osteoarthritis, and depression.[43] Due to increased epidermal cell turnover, psoriasis leads to elevated uric acid production. At the same time, patients with CKD experience reduced urate excretion, resulting in hyperuricemia and an increased risk of incident gout.[44] 

Gout is associated with a heightened risk of ischemic heart disease (hazard ratio [HR], 1.86), MI (HR, 3.246), and cerebrovascular disease (HR, 1.552).[45] Moreover, individuals with recent gout flares experience a transient increase in cardiovascular events.[46]

Gout is linked to increased overall mortality, encompassing all-cause mortality and specific causes such as cardiovascular disease, infectious disease, and cancer-related deaths.[47] Particularly, gout is strongly associated with elevated cardiovascular mortality [48] and contributes to mortality related to renal disease, digestive diseases, and dementia.[49]

The connection between gout and dementia, including Parkinson disease, is complex and not fully understood. Studies have shown varied associations, with some indicating a lower risk of dementia,[50][51][52] specifically Alzheimer disease,[53][54] in individuals with hyperuricemia and gout. However, conflicting data suggest that hyperuricemia and gout are associated with an increased risk of dementia.[55][56] Similarly, the relationship between gout and Parkinson disease remains inconclusive, with studies reporting differing results, including lower,[57][58][59] no specific,[60][61] or higher risk of Parkinson disease in patients with gout.[62]

Pathophysiology

Gout is an inflammatory arthritis triggered by the deposition of MSU crystals in joints, soft tissues, and bones. The pathophysiology of gout involves a series of complex and interacting processes as follows:[63]

(1) Genetic and metabolic contributors to hyperuricemia

(2) Biochemical factors favoring MSU crystal formation

(3) Inflammatory responses to MSU deposition

(4) Immune-mediated resolution of inflammation

(5) Chronic crystal–cell interactions cause cartilage attrition, bone erosion, and tophi formation.

Uric Acid Physiology

Uric acid is the final product of purine metabolism in humans due to a genetic mutation in the gene encoding the enzyme uricase.[9][10] Traditionally, it was believed that uric acid played a crucial role as a natural antioxidant in the human body. However, recent studies highlight its role in immune surveillance, blood pressure regulation, and intravascular volume regulation.

At physiologic pH (7.4), uric acid exists mainly as ionized MSU, which has limited solubility. In acidic environments such as urine, the nonionized form is even less soluble, predisposing to the formation of uric acid stones, distinct from MSU crystals in gout.[9]

Most urate in the body is produced endogenously in the liver, with a minor contribution from the small intestines. Renal excretion is pivotal in managing the body's urate pool under steady-state conditions since the glomerulus filters nearly all urate. In a hyperuricemic state, the urate pool expands. Normal urate range differs between genders. In men, it is 800 to 1000 mg; in women, it ranges from 500 to 1000 mg. The daily turnover of urate ranges between 500 and 1000mg. During male puberty, serum urate concentrations increase to reach the adult range, whereas urate levels remain low in females of reproductive age. This disparity is attributed to estrogen's influence on renal urate transporters, which reduces renal urate reabsorption and increases clearance in women. However, in menopausal and postmenopausal women, urate levels approach those of adult males and may be influenced by hormone replacement therapies.[9]

The following distinguishes between causes of lower and higher urate levels:

Lowered urate pool                        Raised urate pool

Table

Hyperuricemia

Hyperuricemia is central to gout pathogenesis, as it promotes the nucleation and growth of MSU crystals by decreasing urate solubility. Contributing factors include the genetic absence of uricase, reabsorption of approximately 90% of filtered uric acid, and the limited solubility of MSU and urate in body fluids. An imbalance between uric acid production and excretion results in elevated serum uric acid levels.[64]

When renal urate excretion is impaired, intestinal uricolysis compensates for up to half of total urate disposal, with the ABCG2 transporter playing a key role. Serum urate concentrations above 6.8 mg/dL result in supersaturation, increasing the risk of crystal deposition. Hyperuricemia affects approximately 20% of adult White men in the United States and is linked to multiple chronic disorders.

Hyperuricemia can be classified as either primary (idiopathic) or secondary. Overproduction of uric acid is observed in several diseases, toxic states, and due to certain medications. Examples include acute leukemia, tumor lysis syndrome, and psoriasis.

Purine Metabolism

Purines consist of 9-carbon purine nuclei that form fused pyrimidine and imidazole rings. Purines perform essential functions in all living cells through purine-based nucleic acids, including adenine, guanine, and hypoxanthine. The contribution of dietary purines to the urate pool is significant. Removing purines from the diet of normal individuals for 10 days reduces urate levels by 25% and urinary uric acid excretion by 50%. However, implementing severely purine-restricted diets is impractical. Conversely, diets high in fructose, meat, alcohol, and fish are associated with an increased risk of hyperuricemia.[15]

The endogenous pathway of purine production, known as de novo purine synthesis, involves the conversion of ribose-5-phosphate from 5-phosphoribosyl 1-pyrophosphate (PRPP) into nucleotide inosine monophosphate through 10 key steps. This energy-intensive process prompts energy conservation through the interconversion and salvage of purine nucleotides. Urate precursors of purine degradation are hypoxanthine and guanine, most of which are salvaged. Unused guanine is deaminated to become xanthine, while hypoxanthine is oxidized to xanthine by xanthine oxidase.[9]

Xanthine oxidase is a flavoprotein containing molybdenum-pterin and iron sulfide clusters. It operates in 2 forms: as an oxidase, utilizing oxygen to convert hypoxanthine to xanthine and then to urate, and as a dehydrogenase, using nicotinamide adenine dinucleotide (NAD+). Inhibiting xanthine oxidase is the primary target for lowering urate levels in patients with gout.

The primary regulatory steps in purine synthesis include:

1. The synthesis of PRPP in the PRPP synthetase pathway.
2. The utilization of PRPP in the first step of de novo purine synthesis.

The pathway is regulated by inhibition via purine nucleotide products of purine synthesis and by activation via increased PRPP. This antagonistic control mechanism is disrupted in 2 rare X-linked disorders: deficiency of the salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and overactivity of PRPP synthetase (PRS1). Conditions such as excessive adenosine triphosphate (ATP) depletion during tissue hypoxia or acute alcohol intoxication can lead to decreased concentrations of inhibitory nucleotides and excess urate production.

Renal Uric Acid Secretion

Although all urate is filtered, only 5% to 10% is excreted because about 90% is reabsorbed. Thus, patients with hyperuricemia due to impaired excretion may have normal urinary urate levels. Genomic studies identify multiple renal transporters; GLUT9 and URAT1 have the greatest effect on serum urate.[7][65]

Glucose Transporter 9 (GLUT9):  Encoded by SLC2A9, GLUT9 is a voltage-driven urate transporter with 2 isoforms (GLUT9L basolateral; GLUT9S apical). It is expressed in renal tubules and the liver, and also transports glucose/fructose. Knockout mice exhibit hyperuricemia, massive uricosuria, and early nephropathy. [7]

URAT1: URAT1 (SLC22A12) reabsorbs urate in exchange for organic anions. Mutations cause hypouricemia and exercise-induced renal dysfunction. Uricosurics (probenecid, benzbromarone, lesinurad) inhibit URAT1. Other transporters include ABCG2, NPT1, NPT4, and MRP4.[7]

Autosomal Dominant Tubulointerstitial Kidney Disease

Mutations in the UMOD gene cause early-onset hyperuricemia (with or without gout), hypertension, and progressive tubulointerstitial fibrosis, leading to end-stage renal disease by approximately age 40. Defective uromodulin alters solute handling in the loop of Henle, reducing Na/Cl reabsorption and increasing proximal tubular urate reabsorption.

Extrarenal Urate Excretion

In the intestines, urate excretion is facilitated by the ABCG2 transporter. Studies in ABCG2-knockout mice have revealed that reduced intestinal urate excretion increases serum urate levels. Consequently, hyperuricemia resulting from urate overproduction can be classified as a renal overload type consisting of extrarenal underexcretion and genuine urate overproduction subtypes. 

Urate Crystal Formation

The formation of MSU crystals requires sustained urate supersaturation. Factors such as the presence of particulate seeds, local cation concentrations, pH, temperature, and dehydration influence crystal formation (see Table. Factors Influencing Urate Crystal Formation).[65][66][67][68] Immunoglobulin G (IgG) may also facilitate crystal formation and growth in patients with gout. MSU crystals tend to form in the first metatarsophalangeal joint, midfoot, and Achilles tendon. Emerging evidence indicates a connection between osteoarthritis and sites of MSU crystal deposition. In osteoarthritic joints, cartilage degradation products, such as chondroitin sulfate, lower urate solubility, thereby promoting nucleation and crystal growth.[66] The solubility of MSU drops rapidly with decreasing temperature, further impacting crystal formation and deposition.[6]

Table

Table 5. Factors Influencing Urate Crystal Formation.

Inflammatory Response

Histopathologic and imaging studies have shown that urate crystals can persist within joints for prolonged periods without causing overt inflammatory reactions. Heavily crystal-laden fluids (urate milk) are sometimes found in uninflamed joints and bursae. The dense urate crystal mass in tophi can sometimes reach massive proportions, accompanied by mild inflammation and symptoms, until it exerts critical compression on surrounding tissues.

The initiation of inflammation in gout typically involves microcrystals shed from preexisting synovial tophi. This is supported by observing acute gout flares, characterized by rapid changes in urate concentrations. The initiation of inflammation depends on multiple factors, including crystal size, the proteins and molecules coating them, and the recruitment of inflammatory cells. MSU crystal surfaces can bind to various proteins, including IgG, lipoproteins, and lipids (see Table. Inflammatory Events in Acute Gout Flare).[9]

The IgG conformational changes promote phagocytosis by cells expressing Fcγ receptors, such as neutrophils and macrophages.[69] IgG also activates the classical complement pathway. MSU crystals can also directly activate the classical and alternative complement pathways, leading to opsonization by depositing the complement split product C3b on the crystals.[70][71] The apolipoprotein coating on the MSU crystals counteracts the opsonic effects of the IgG Fc and complement proteins. Additionally, it inhibits neutrophil stimulation. Thus, the inflammatory potential of MSU crystals is a balance between the proinflammatory and anti-inflammatory elements coating their surface. In acute gout, neutrophils are the predominant inflammatory cells in the synovial tissue and fluid, contributing significantly to the proinflammatory stimulus.[9]

In patients with asymptomatic tophi, synovial fluid macrophages frequently contain MSU microcrystals, suggesting active phagocytic engagement without apparent inflammation. Synovial macrophages and blood monocytes mount a vigorous response to MSU crystals compared to well-differentiated macrophages due to the release of TGF-β1. Researchers have studied 2 main mechanisms by which MSU crystals interact with phagocytes.

1. Activation of phagocytes leads to lysosomal fusion, respiratory burst, and the release of lysosomal enzymes and inflammatory mediators, including TNF-α and IL-8.[63]
2. The predominant pathway of cytosolic protein complex activation involves the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome. MSU crystals activate macrophages and monocytes via toll-like receptors (TLRs) 2 and 4, resulting in signal transduction through MyD88, interleukin-1 receptor-associated kinase 1 (IRAK1), and IRAK4. This activation triggers the nuclear factor-kB, which in turn activates the NLRP3 inflammasome. The activated NLRP3 inflammasome subsequently recruits caspase-1, which processes pro-interleukin-1β (IL-1β) into its active form, IL-1β. IL-1β plays a crucial role in the inflammatory response to gout by promoting vasodilation, recruiting monocytes, and initiating and amplifying the inflammatory cascade. Additionally, IL-1β secretion can result in the breakdown of bone and cartilage. Other cytokines, such as TNF-α, IL-6, and CXCL8, as well as cyclooxygenase-2 (COX-2), are also involved in the inflammatory response.[65][68][72][73][74]

Unlike most external stimuli that activate inflammatory cells through a carefully coordinated cell-surface signal transduction cascade involving tyrosine kinase phosphorylation, MSU crystals bypass this process and directly activate second-messenger systems. 

Table

Table 6. Inflammatory Events in Acute Gout Flare.

Termination of The Acute Flare

Acute gout is inherently self-limiting, even without intervention, typically resolving spontaneously within a few days to a few weeks. This phenomenon is intriguing, given the similarity in the molecular mediators of inflammation between gout and other arthropathies, as well as the persistence of MSU crystals.

Following MSU crystal ingestion, neutrophils undergo NETosis (neutrophil extracellular traps). These NETs aggregate and densely pack MSU crystals while degrading the proinflammatory cytokines, including IL-β, TNF-α, and IL-6. The increased vascular permeability following acute synovitis enables the enhanced entry of anti-inflammatory cytokines and crystal-coating molecules, such as apolipoprotein B (apoB). Coating with apoB and locally produced apoE, as well as transforming growth factor β (TGF-β), inhibits neutrophil activation. Systemic anti-inflammatory mediators, such as melanocortins, reduce joint inflammation via macrophage melanocortin receptors (MCRs). Adenosine monophosphate-activated protein kinase inhibits NLRP3 expression, which in turn inhibits the cleavage of caspase-1 and the secretion of IL-1β.[65][72][74] 

Tophaceous Gout

Tophi are deposits of MSU crystals associated with granulomatous inflammation. They are nests of crystals surrounded by a zone of differentiated macrophages and multinucleated giant cells encased within a fibrous layer. Proinflammatory cytokines like IL-1 and TNF-α are expressed within the corona. Aggregated NETs are also part of the tophus. The tophus is a dynamic, complex, and organized chronic inflammatory response to MSU crystal deposition.

Tophi are primarily found in periarticular, articular, and subcutaneous areas, including cartilage, bone, joints, tendons, and skin, all of which are rich in proteoglycan. The tissue reaction to tophus is generally characterized by chronic inflammation, involving both adaptive and innate immunity. Few patients with tophaceous gout also present with chronic gouty arthritis (chronic synovitis). There is a close relationship between MSU crystal deposits and the development of cartilage and bone erosions.[75] 

Tophi contribute to joint damage and bone erosion in gout.[76] At the bona and a tophus interface, MSU crystal deposits are surrounded by osteoclast-like cells.[77] T-cells within the tophus express the receptor activator of nuclear factor κB ligand (RANKL), contributing to bony erosions. Additionally, urate crystals decrease the function, viability, and differentiation of osteoblasts and reduce osteoprotegerin expression. Hence, more osteoclasts and reduced osteoblasts are present at the bone-tophus interface.

The double-contoured ultrasound sign is observed in the superficial articular cartilage of patients with chronic gout and represents the presence of urate deposits. Urate crystals degrade cartilage matrix by inducing nitric oxide generation and the expression of matrix metalloprotease 3. Consequently, joints with persistent crystals experience ongoing progressive damage in the absence of acute flares. 

Histopathology

When examined under polarized light microscopy, MSU crystal deposition is typically described as a rod or long, needle-shaped crystal with negative birefringence.[78] When viewed under light microscopy, tophi exhibit distinct zones: the crystalline center, the surrounding corona zone, and the fibrovascular zone. The corona zone contains multinucleated giant cells, histiocytes, and plasma cells.[79]

History and Physical

A thorough history and physical examination are essential for recognizing the characteristic clinical features of gout and identifying potential risk factors. Evaluation should focus on the pattern of joint involvement, timing and severity of flares, associated comorbidities, medication use, and the presence of tophi or other signs of chronic disease.

Gout has been described as a chronic disease characterized by 4 distinct stages. These stages reflect the progression of the disease and are as follows:[4]

1. Asymptomatic hyperuricemia
2. Acute gout attacks
3. Intercritical period
4. Chronic tophaceous gout

Asymptomatic Hyperuricemia

The majority of patients with asymptomatic hyperuricemia never develop gout. The risk of an acute gout attack increases with the serum urate level. This stage ends with the first gout attack.

Acute Gout Attack

The initial clinical presentation of gout is an acute episode of monoarticular arthritis, typically with abrupt onset of severe pain, redness, and swelling, peaking within 12 to 24 hours. The condition is usually monoarticular, with 85% to 90% of cases affecting the lower limbs.[4][80] The first metatarsophalangeal joint is the most common site (see Image. Acute Gout Involving the First Metatarsophalangeal Joint), accounting for approximately 50% of initial attacks (podagra), and nearly 90% of patients develop podagra during the course of the disease.[2] Other commonly affected joints include the ankle, knee, and tarsal joints, as well as tendons and bursae. Axial involvement, including the sacroiliac joints and spine, is uncommon.[81][82]

Acute attacks can be precipitated by local trauma, alcohol binges, overeating or fasting, weight changes, use of diuretics, and initiation of urate-lowering drugs. In a hospital setting, postoperative status or acute severe medical illnesses such as MI, exacerbation of CHF, or cerebrovascular accident may precipitate attacks.[4] Acute gouty arthritis may be associated with fever and leukocytosis, making it difficult to differentiate from septic arthritis. Gout flares are more common at night and in the early morning hours.[83] The pain is often sudden, waking the patient from sleep, or it may have developed gradually over a few hours before presentation.[83]

Signs of inflammation may extend beyond the joint involved, giving the impression of cellulitis with erythema and desquamation. Systemic inflammatory features may include fever, malaise, and fatigue.[2] The initial attack resolves within 3 to 14 days, even without treatment. Over time, gout flares may become less severe but may involve more joints.[4]  Around 60% of the patients experience a second attack within 1 year, and 80% within 3 years. Polyarticular gout flares are more likely to occur in patients with longstanding disease.

During an acute gout flare, patients typically present with a warm, erythematous, and swollen joint that is extremely tender to touch. When more than 4 joints are affected, the pattern is described as polyarticular gout; if 4 or fewer are involved, it is oligoarticular. In advanced disease, flares may become systemic, occasionally mimicking sepsis. [84][85] Tophi—firm, subcutaneous deposits of MSU crystals—develop in individuals with longstanding hyperuricemia and are most often found around the joints, ears, finger pads, tendons, and bursae. [2]

Intercritical Gout

After resolving the acute attack, the patient enters the intercritical stage. Patients typically feel well during this stage without experiencing joint pain or swelling. Despite the apparent inactivity of the disease, hyperuricemia persists, and crystal deposition continues. Subclinical inflammation may be present in the joints during this period. If left untreated, the intercritical period shortens with more active flare-ups of the disease. 

Chronic Tophaceous Gout

Patients with gout who are untreated or undertreated may develop chronic tophaceous gout over several years, leading to gradual progressive joint destruction. Gouty tophi, which are foreign bodies surrounded by granulomas containing deposits of MSU crystal, manifest as chalk-like subcutaneous nodules beneath transparent skin with increased vascularity. These nodules may or may not drain. While some patients may present with tophi as their initial symptom, chronic tophaceous gout usually develops 10 or more years after an acute attack (see Image. Aricular Tophus in Chronic Gout). However, microtophi can be observed early in the disease, especially in patients with hyperuricemia. MSU crystal deposition is evident in joints affected by osteoarthritis, primarily in the connective tissue and articular cartilage.

Tophi may occur intra-articularly, periarticularly, or extra-articularly, with common sites including the digits of hands and feet (see Image. Tophaceous Gout Affecting the Hands), knees, and the olecranon bursa. This condition leads to destructive deforming arthritis, extensive bone destruction, and severe deformities. Women develop tophaceous deposits on the Heberden nodes and Bouchard nodes. Finger pad tophi were observed in 30% of patients with chronic tophaceous gout. Postmenopausal women with CKD may exhibit finger pad tophi before the onset of an acute attack.[4][3][65]

Tophaceous deposits have been documented in various uncommon sites, including the cornea and heart valves. These deposits underscore the systemic nature of gout and its capacity to affect various tissues and organs beyond the joints.

Evaluation

The evaluation of gout focuses on confirming the diagnosis, identifying crystal deposition, and assessing the disease's severity and extent. A comprehensive assessment includes clinical history, physical examination, laboratory testing, and, when appropriate, synovial fluid analysis and imaging studies.

Synovial Fluid Analysis

MSU crystal identification remains the gold standard for diagnosing gout.[78] Gout flares are characterized by the presence of MSU crystals in synovial fluid from affected joints or bursae, visualized using compensated polarized light microscopy. The crystals are often intracellular, indicating active phagocytosis. This technique can also identify uric acid crystals from tophaceous deposits and joints during the intercritical period.[86] During a gout flare-up, the synovial fluid is typically yellow and cloudy, containing crystals and white blood cells (WBCs), predominantly neutrophils.

In patients with septic arthritis, the synovial fluid will be more opaque, with a yellow-green appearance. Microscopic examination reveals a higher white blood cell (WBC) count (>50,000/microL) with a predominance of neutrophils. However, there is considerable overlap in WBC counts and neutrophil percentages between patients with acute gouty arthritis and those with septic arthritis, rendering these parameters unreliable for diagnosis. Positive synovial fluid gram stains and cultures, along with low synovial fluid glucose levels, are common findings in septic arthritis. It is essential to note that the presence of crystals in synovial fluid analysis does not rule out septic arthritis, as both conditions can coexist.[87][88]

Under polarizing microscopy, synovial fluid or tophus aspiration analysis reveals needle-shaped, negatively birefringent crystals.[2][4][89] Arthrocentesis is essential to confirm the diagnosis and differentiate it from other conditions such as septic arthritis, Lyme disease, or pseudogout (caused by calcium pyrophosphate crystals).[89]

Laboratory Study

The examination typically reveals elevations in the WBC count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels during acute gouty arthritis. These features are nonspecific and do not confirm or differentiate the diagnosis from septic arthritis.[87]

During acute gouty arthritis, the serum urate level may be high, normal, or low. Approximately 50% of patients with acute gouty arthritis do not have an elevated serum uric acid level. Serum uric acid measurement during an acute attack is of no diagnostic value; it is most useful when checked after the resolution of the flare. Hyperuricemia is helpful in the clinical diagnosis of gout in symptomatic patients, but hyperuricemia alone does not confirm the diagnosis. Asymptomatic hyperuricemia is not uncommon in the general population. Persistently low serum uric acid concentrations make the diagnosis of gout unlikely.[4] In patients suspected of having gout based on clinical features, an elevated serum uric acid level (>6.8 mg/dL) can support the diagnosis but is neither diagnostic nor required to confirm it. The most accurate time to assess serum urate level to establish a baseline value is 2 weeks or more after a gout flare has subsided.

Urinary fractional excretion of uric acid can be measured, especially in young populations with nonspecific causes of hyperuricemia. The measurement can help differentiate between overproduction and underexcretion of uric acid and can guide therapy.

Imaging

Radiographs of the affected joint may show gouty erosions. These are often described as "rat bite" or "punched-out" erosions with thin overhanging edges (see Image. Hand Radiograph of Chronic Gout). Although not routinely used, ultrasonography and dual-energy computed tomography (DECT) can assist in diagnosing gout.[90][91][92][93] On ultrasound, MSU deposition appears as a hyperechoic enhancement over the cartilage, known as the double contour sign. DECT can be used to identify urate deposits by measuring beam attenuation after exposure to 2 different x-ray spectra.[2][4] In a pooled analysis, the ultrasound double-contour sign had a sensitivity of 83% and a specificity of 76%, whereas DECT had a sensitivity of 87% and a specificity of 84% for diagnosing gout.[91] A meta-analysis of ultrasound diagnostic accuracy, including features such as the double-contour sign, tophus, and bony erosion, showed a sensitivity of 65.1% and a specificity of 89% for diagnosing gout.[94] 

Treatment / Management

Early initiation of treatment during a gout flare leads to more rapid symptom resolution, and the duration of therapy ranges from a few days to several weeks, depending on how promptly treatment is initiated. Prophylaxis to prevent gout flares should generally be continued for 3 to 6 months during the early phase of urate-lowering therapy (ULT). In patients already receiving ULT at the time of a flare, therapy should be continued without interruption, as temporary discontinuation provides no benefit. The presence of tophi necessitates long-term ULT, either during or after a gout flare, to prevent or reverse joint damage and chronic gouty arthritis.

Acute Gout Flare

The management of acute gouty arthritis flares aims to reduce inflammation and associated pain. If possible, treatment should commence within the first 24 hours of onset to reduce the severity and duration of the flare-up.[64] Nonpharmacological management, such as rest and topical ice packs, can be combined with anti-inflammatory medications. [95][96] First-line treatments for gout flares are nonsteroidal anti-inflammatory drugs (NSAIDs), colchicine, systemic glucocorticoids, or, in some rare cases, IL-1 inhibitors.[97] The treatment duration should be at least 7 to 10 days to prevent rebound flare-ups.[98] The choice of initial treatment is based on patient factors, including comorbidities, access to medications, and prior medication experience. 

1. NSAIDs

NSAIDs are most effective when therapy is initiated within 48 hours of the onset of gout symptoms. Indomethacin and naproxen are the more potent NSAIDs for gout, although many other commonly used NSAIDs exist. NSAID names and dosing are as follows:

• Indomethacin 50 mg 3 times daily
• Naproxen 500 mg twice daily
• Ibuprofen 800 mg 3 times daily
• Diclofenac 50 mg 2 to 3 times daily
• Celecoxib 200 mg 2 daily

Typically, NSAID treatment for a gout flare lasts for 5 to 7 days. There is no significant preference for one NSAID over another, but high-dose, fast-acting NSAIDs such as naproxen or diclofenac are options.[64] NSAIDs are usually given in full doses for the first 3 days and then tapered according to the clinical improvement. COX-2 selective inhibitors, such as celecoxib, can be used to reduce adverse gastrointestinal effects.

Contraindications for the use of NSAIDs include active duodenal or gastric ulcer, cardiovascular disease (uncontrolled hypertension or CHF), NSAID allergy, and CKD with creatinine clearance (CrCl) of less than 60 ml/minute per 1.73 square meters. Aspirin is not recommended for treating gout flares due to the paradoxical effects of salicylic acid on serum urate levels.[99][100] This paradoxical effect results from uricosuria at higher doses and renal uric acid retention at lower doses (<2-3 g/day).[101][102]

2. Corticosteroids

Glucocorticoids are recommended for acute gout flare and are particularly beneficial in polyarticular flare and in patients with contraindications to NSAIDs and colchicine, including patients with renal insufficiency. The initial dose for a gout flare is:

• Prednisolone or prednisone 30 to 40 mg once daily or divided into twice-daily doses until resolution begins. Taper the dose over the next 5 to 10 days.

High starting doses of systemic steroids (>0.5 mg/kg body weight) are required for acute gout, especially in patients with a polyarticular presentation. A depot preparation for triamcinolone (40-60 mg once) or methylprednisolone may be considered in patients who are unable to tolerate oral corticosteroids.[103][104] However, the dose may need to be repeated every 48 hours to resolve the flare. Glucocorticoids can be administered intra-articularly for monoarticular gout flare-ups. The efficacy of glucocorticoids is similar to or superior to that of other agents, and they have no greater risk of adverse effects in most patients.[105][106][107]

In patients with an unclear diagnosis of an acute gout flare, arthrocentesis and synovial fluid analysis should be performed. Oral and intra-articular glucocorticoids should be avoided until results are available due to concern about worsening septic arthritis if present. In such cases, NSAIDs or colchicine should be considered. Frequent adverse effects of moderate-to-high-dose, short-term glucocorticoid use include hyperglycemia, increased blood pressure, and mood changes. Frequent use of glucocorticoids should be avoided to limit long-term adverse effects, including osteopenia, increased risk of infections, hyperglycemia, etc. 

In patients with concomitant or suspected infections, uncontrolled diabetes mellitus, prior glucocorticoid intolerance, and post-operative status, glucocorticoids may heighten the risk of impaired wound healing. Careful consideration of these factors is crucial when determining the appropriate course of treatment for patients with gout flares.

Intravenous or intramuscular glucocorticoids are recommended for patients who are not candidates for intra-articular glucocorticoid injection or who are unable to take oral medications. A typical methylprednisolone dose is 20 mg intravenously twice daily, with a stepwise reduction and rapid transition to oral prednisone when improvement begins. Adrenocorticotropic hormone (ACTH) is also efficacious for treating gout flare, but limited availability and high cost restrict its use.

3. Colchicine

Colchicine, derived from Colchicum autumnale and used for over 3,500 years, remains an important option for treating acute gout. [108] It is most effective when taken within 24 hours of flare onset and has demonstrated over 50% pain reduction at 24 hours compared with placebo in randomized trials. 

Colchicine is lipophilic and rapidly taken up by cells after oral administration. Its primary target is tubulin: colchicine binds unpolymerized tubulin and forms a colchicine–tubulin complex that disrupts microtubule function. This affects multiple cellular processes, including cell proliferation, gene expression, signal transduction, chemotaxis, and neutrophil degranulation. Colchicine also reduces neutrophil adhesion by inhibiting the redistribution of E-selectin on endothelial cells.

For acute gout flares, EULAR and FDA-endorsed low-dose regimens recommend a maximum of 1.8 mg on day 1:

• 1.2 mg at the first sign of the flare, followed by 0.6 mg 1 hour later (FDA-approved regimen), or
• 0.6 mg 3 times on the first day, not exceeding 1.8 mg in 24 hours.[109] 
  On subsequent days, colchicine should be taken once or twice daily until the gout flare resolves.[110]

Dose reduction is required in patients with hepatic or renal impairment and in those at risk for significant drug interactions. High-dose colchicine regimens should be avoided because they are associated with substantial toxicity. Colchicine toxicity is more likely with concomitant use of P-glycoprotein (ABCB1) inhibitors and strong CYP3A4 inhibitors (eg, cyclosporine, clarithromycin), and neuromyopathy can develop after weeks of combined cyclosporine and colchicine therapy.

Adverse effects include gastrointestinal symptoms (nausea, abdominal cramping, diarrhea), myotoxicity, and myelosuppression (leukopenia, thrombocytopenia, aplastic anemia), with gastrointestinal symptoms being the most common. Intravenous colchicine is strongly discouraged due to the risk of serious adverse events, including fatal toxicity, and is no longer FDA-approved in the United States.[111] The most common adverse effects are abdominal cramping and diarrhea.[109][112] 

In high-risk patient groups, colchicine dosing must be further reduced, often to a single 0.3 mg dose on the day of the flare with no repeat dosing for at least 3 to 7 days or longer. High-risk patients include:

• Those who received colchicine prophylaxis within the last 14 days and have normal renal and hepatic function, but are taking potent P-glycoprotein or CYP3A4 inhibitors
• Those who used colchicine prophylaxis within the last 14 days and are on moderate CYP3A4 inhibitors
• Patients with advanced hepatic or renal impairment (eg, Child-Pugh C cirrhosis or CrCl <30 mL/min), regardless of recent colchicine exposure

Colchicine exhibits interesting effects beyond treating and preventing gouty arthritis flares. Research suggests it has a beneficial effect on cardiovascular events.[108][113][114] A population study linked colchicine use in patients with gout to reduced cardiovascular events and all-cause mortality.[115] In a randomized, double-blind trial involving post-MI patients within 30 days (n = 4,745), low-dose colchicine use lowered the risk of cardiovascular events (resuscitated cardiac arrest, MI, stroke, and angina leading to revascularization) compared to placebo: 5.5% with colchicine versus 7.1% with placebo; HR 0.77 (95% CI 0.61-0.96; P=0.02).[116] While colchicine did not affect outcomes like death from cardiovascular causes, resuscitated cardiac arrest, or MI, it notably reduced stroke and angina, leading to coronary revascularization.

4. Interleukin-1 inhibition

In patients who have contraindications or who poorly tolerate NSAIDs, colchicine, or glucocorticoids, IL-1 inhibitors for gout flare should be considered. These are not recommended as first-line agents due to their higher cost and limited access to the medication. Anakinra, a soluble IL-1 receptor antagonist, is administered subcutaneously at 100 mg/day for 3 days, or a single dose of the IL-1 beta monoclonal antibody, canakinumab, can be administered.[117][118] The subcutaneous dose of canakinumab 150 mg was more effective than a single intramuscular dose of triamcinolone acetonide, although the risk-benefit ratio is uncertain.

Anti-Inflammatory Prophylaxis For Acute Gout

Initiation of ULT is associated with an increased risk of gout flares, and hence, anti-inflammatory prophylaxis is recommended. For prophylaxis, colchicine therapy, NSAIDs, and corticosteroids may be considered. [119][120] It is commenced 1 or 2 weeks before using urate-lowering drugs and continued for up to 6 months after normalizing uric acid levels. [120][119] [121] The recommended colchicine dosage is 0.6 mg once or twice daily in patients without renal or hepatobiliary compromise. In patients with renal impairment, the colchicine dose may be reduced to 0.3 mg daily or 0.6 mg every other day. 

Management of Chronic Gout 

Non-pharmacologic treatment

Gout is associated with several comorbidities, including obesity.[37] In a study examining the association between obesity and gout, adults aged 40 to 75 years (n = 11,079) in NHANES 2007 to 2014 were categorized into 4 groups: stable obese, weight gain, weight loss, and those maintaining a normal BMI over time (reference group).[39] Among those with stable obesity, the risk of gout was the highest, with an HR of 1.84 (95% CI 1.08-3.14). Patients who gained weight as adults also exhibited an increased risk of gout with an HR of 1.65 (95% CI 1.19-2.29).

Diet can affect serum uric acid levels. Weight loss and dietary adjustments can reduce serum uric acid by 1 to 2 mg/dL. Foods high in purines, such as organ meats, shellfish, and beer, can elevate uric acid levels. Soft drinks containing high-fructose corn syrup are associated with an increased risk of gout;[12][13] therefore, reducing their intake can help lower serum uric acid levels. Adoption of the DASH diet has been associated with lower serum urate compared with a typical Western diet. Higher vitamin C intake (≥500 mg/day) has been linked to lower serum urate and a reduced risk of incident gout, with some studies suggesting a dose–response relationship at higher vitamin C doses in men.[16][18][19][20][21][22] Cherry consumption has been associated with lower serum urate and decreased risk of recurrent gout attacks in observational studies.[23][24]

Urate-lowering therapy

The 2020 American College of Rheumatology guideline advises against initiating ULT after a first, uncomplicated episode of acute gout and against prescribing ULT for asymptomatic hyperuricemia.[122]

ULT is generally indicated in patients with:

• Frequent or disabling gout flares (≥2 per year)
• One or more subcutaneous tophi
• Radiographic evidence of joint damage due to gout
• A single flare in the setting of CKD stage ≥3, urolithiasis, or serum urate (SU) >9 mg/dL

The decision to start ULT should be individualized and shared with the patient.

ULT should be initiated at low doses (e, allopurinol ≤100 mg/day, febuxostat ≤40 mg/day) and titrated every 2 to 6 weeks to achieve a target SU of <6 mg/dL, or <5 mg/dL in patients with tophi. Starting ULT during an acute flare is conditionally recommended if adequate anti-inflammatory therapy is administered.[122][123] The 2020 American College of Rheumatology Guideline conditionally recommends starting ULT during acute gout flares.[124][125][126] 

During ULT initiation, there is an increased risk of gout flares. Prophylactic anti-inflammatory therapy is recommended at the initiation of ULT and is preferable to continue for up to 6 months. [122]

ULT can be categorized into 3 classes based on their mechanisms:

1. Xanthine oxidase inhibitors  

Xanthine oxidase inhibitors (XOIs) work by inhibiting uric acid synthesis. This class includes allopurinol and febuxostat. Allopurinol is the recommended first-line pharmacological ULT in gout.[122] Physicians should regularly monitor liver enzymes, renal function, and blood count. Adverse effects from allopurinol can range from skin rashes to life-threatening severe allopurinol hypersensitivity, especially in HLA-B*5801-positive patients.[2][122]

   a. allopurinol

Allopurinol is converted to its active metabolite, oxypurinol, in the liver and has a half-life of approximately 24 hours. The initial allopurinol dose is 100 mg daily in patients with CrCl greater than 60 mL/min, and the dose is titrated upward by 100 mg every 2 to 4 weeks. A daily dose of 300 mg of allopurinol reduces serum urate levels in 33% of the population. Allopurinol can be increased above 300 mg daily to achieve the target serum uric acid.

Allopurinol is taken once daily. Medications such as allopurinol and oxypurinol lower serum urate levels through a dual mechanism: inhibition of xanthine oxidase and interference with the purine salvage pathway by competing with phosphoribosylpyrophosphate, as well as suppression of aminotransferase activity by their nucleotide metabolites. Allopurinol also nonselectively inhibits pyrimidine metabolism. In patients with stage 3 or greater CKD, the starting dose of allopurinol should be 50 mg daily.[122] 

Adverse effects associated with allopurinol include the potential to trigger gout flares, pruritic and maculopapular rashes, leukopenia, thrombocytopenia, diarrhea, and severe cutaneous adverse reactions. Bone marrow suppression is uncommon but may occur at very high doses or in patients with CKD. Allopurinol can lead to a drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome, a life-threatening response to allopurinol.

Major hypersensitivity reactions like Stevens-Johnson syndrome or toxic epidermal necrolysis may occur in major allopurinol hypersensitivity syndrome (AHS). The highest risk for AHS occurs in the first 60 days after initiating allopurinol therapy. Patients who carry the HLA-B*5801 allele are at increased risk for developing severe hypersensitivity reactions, which are more common in people of Han Chinese, Korean, or Thai descent.[122][127] Testing for this allele is recommended in patients of Southeast Asian descent and African American patients. Starting at a low dose and gradually increasing it can decrease the risk of adverse reactions. The recommended starting dose is 1.5 mg per unit of estimated GFR.[128] Interestingly, allopurinol can be safely increased above 300 mg daily, even in patients with CKD, to achieve the target serum uric acid level.[129]

Allopurinol can enhance the cytolytic and immunosuppressive effects of azathioprine and 6-mercaptopurine (6-MP), as these drugs are partially metabolized by xanthine oxidase.[130] Therefore, allopurinol should be avoided in patients receiving these agents.[131] Additionally, in patients on warfarin, their anticoagulation status must be carefully monitored when allopurinol is prescribed.

  b. Febuxostat

Febuxostat is a selective XOI that occupies the access channel to the molybdenum-pterin active site of the enzyme. Renal elimination plays a minor role in the pharmacokinetics of febuxostat. FDA approval for febuxostat in treating patients with gout and hyperuricemia includes initial daily doses of 40 mg. If the urate levels do not normalize within 2 weeks, the dosage is increased to 80 mg daily. Studies have demonstrated the superior efficacy of febuxostat compared with allopurinol (maximum dose of 300 mg daily).[132][133] However, febuxostat may be more common with allopurinol than cardiovascular and hepatic abnormalities. In patients with CKD, febuxostat exhibits a more potent urate-lowering effect than allopurinol. Febuxostat has a distinct chemical structure, making it an option for patients who have experienced hypersensitivity reactions to allopurinol. Patients taking azathioprine, 6-MP, and theophylline are considered contraindicated for the use of febuxostat.

In the CARES trial, which focused on cardiovascular safety in patients with gout and a history of cardiovascular disease, febuxostat and allopurinol were compared.[134] The primary endpoint, a composite of cardiovascular death, nonfatal MI, nonfatal stroke, or unstable angina requiring revascularization, showed no significant difference between the two drugs. However, febuxostat was associated with an increased risk of cardiovascular death (HR, 1.34; 95% CI, 1.03-1.73; P = 0.03) and higher all-cause mortality (HR, 1.22; 95% CI, 1.01-1.47; P = 0.04). Some population studies have also shown an increased risk of cardiovascular events and death.[135][136] However, some studies do not show an increased risk of cardiovascular events, including a randomized, open-label noninferiority study, 2 population studies, and a systematic review.[137][138][139][140][139][138][137] In a follow-up investigation of the CARES trial, patients who discontinued ULT experienced increased cardiovascular events and deaths at 30 days and 6 months.[141] 

The Febuxostat versus Allopurinol Streamlined Trial (FAST), published in The Lancet in 2020, is the key study that challenged the cardiovascular mortality concerns raised by CARES. This large randomized controlled trial of over 6,000 patients with gout found that febuxostat was not associated with increased cardiovascular death or all-cause death compared to allopurinol, with actually fewer deaths observed in the febuxostat group.[142] A subsequent meta-analysis concluded that in patients without atherosclerotic disease, febuxostat likely has a cardiovascular profile similar to that of allopurinol.[143]

Allopurinol and febuxostat are similarly effective, although some data suggest that febuxostat may be more effective in patients with CKD. In a comparative noninferiority trial of allopurinol and febuxostat, in which at least 33% of patients had stage 3 CKD, both drugs showed similar efficacy in managing flares and in reducing serum uric acid levels to the target range.[144]

XOIs have demonstrated various effects, particularly in population-based studies of cardiovascular disease.[145] The theory is that chronic hyperuricemia and MSU deposition result in chronic inflammation, thereby enhancing the progression of atherosclerosis. Notably, allopurinol has been associated with a modest reduction in all-cause mortality among patients with gout.[146][147] A case-matched cohort study conducted in Taiwan revealed that patients with gout faced an increased risk of cardiovascular and all-cause mortality. However, ULT treatment was associated with reduced risk of cardiovascular (HR 0.29, 95% CI 0.11-0.80) and all-cause mortality (HR 0.47, 95% CI 0.29-0.79).[148] Allopurinol use was correlated with a lower risk of developing incident atrial fibrillation.[149] 

ULT may also slow the progression of CKD [150][151][137][138], and allopurinol is associated with a lower risk of incident renal disease in elderly patients compared to febuxostat.[139] Literature suggests that ULT in gout patients might affect outcomes, including dementia, erectile dysfunction, and other comorbidities. While some controlled trials have examined the effect of allopurinol on the incidence of cardiovascular events, renal disease, and DM, these studies were conducted in at-risk patients, not specifically in those with gout. Therefore, the relevance of these findings to patients with gout remains unclear. 

2. Uricosuric Drugs 

Uricosuric agents increase renal urate clearance.[2][65] Patients with low or normal urinary uric acid excretion despite hyperuricemia are potential candidates for uricosuric therapy. Drugs in this class include probenecid and lesinurad (withdrawn from the US market). These agents inhibit URAT1 at the apical membrane of renal proximal tubular epithelial cells. However, they are ineffective as monotherapy in patients with low creatinine clearance (<30 mL/min) and contraindicated in patients with a history of nephrolithiasis.[140] 

Probenecid, the only agent approved as a monotherapy, is initiated at 250 mg twice daily. Dose adjustments are made based on serum urate concentration, with increments every few weeks. The usual maintenance dose ranges from 500 to 1000 mg (taken 2 to 3 times daily), aiming to achieve target urate levels of less than 6 mg/dL (<357 µmol/L).

The significant adverse effects of uricosuric drugs are the precipitation of a gout flare, uric acid urolithiasis, gastrointestinal intolerance, and rash. Uricosuric agents are not appropriate for patients with CKD and a creatinine clearance of less than 60 mL/min. Patients with tophi are best treated with XOIs or pegloticase.

3. Uricase Pegloticase (urate oxidase)

Uricase is present in nonprimates and lower primates. Pegloticase, a pegylated recombinant form of uricase, is a potent agent that rapidly reduces serum urate levels by directly degrading uric acid into highly soluble allantoin. Polyethylene glycol (PEG) molecules are attached to the recombinant porcine-baboon uricase in a process known as PEGylation.This process extends the PEG molecule's half-life to days or weeks, decreasing but not eliminating immunogenicity.[152] 

Pegloticase is reserved for patients with refractory gout, usually those with a high tophaceous burden. Patients must discontinue ULT therapy when starting this medication because antibodies to pegloticase may develop. The recommended dosing is 8 mg every 2 weeks, administered as an intravenous infusion, coadministered with weekly oral methotrexate 15 mg [153]. Before each infusion, serum urate levels should be monitored to confirm urate-lowering efficacy. If serum uric acid rises above 4 mg/dL, the infusions should be stopped, as this indicates the patient is developing antibodies to pegloticase, which could lead to infusion reactions.

Pegloticase has effectively lowered serum uric acid levels in patients with refractory gout, as evidenced by both short-term and long-term clinical trials.[154][155] Phase 3 studies revealed complete resolution of 1 or more tophi in 20% of patients by 13 weeks and uric acid levels below 6 mg/dL in 42% of subjects within 6 months.[156] During the first 6 months of pegloticase therapy, all patients should receive prophylaxis for gout flares.

Due to the risk of severe hemolytic anemia, pegloticase is contraindicated in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Acute gout flares are observed in 80% of patients during the first few months of pegloticase therapy, even with prophylactic measures in place. Moderate infusion reactions like flushing, urticaria, and hypotension are expected, with 2% of patients experiencing severe reactions like anaphylaxis. Some reactions, such as severe muscle pain and cramping, occur due to unknown mechanisms. Efforts to reduce the immunogenicity of pegloticase, particularly when used with methotrexate or mycophenolate mofetil, have proven practical; however, infusion reactions remain a significant issue.

Rasburicase, a nonpegylated recombinant uricase, has not received FDA approval for the treatment of gout. It prevents acute uric acid nephropathy due to tumor lysis syndrome in patients with high-risk leukemia and lymphoma.

Other Drugs with an Effect on Serum Uric Acid

Several drugs used to treat conditions such as hypertension, type 2 diabetes, and hyperlipidemia can affect serum uric acid levels (see Table. Urate-Lowering Drugs and Mechanisms and Table. Urate-Increasing Drugs and Mechanisms).[157] The sodium-glucose cotransporter-2 inhibitors (SGLT2i) are particularly noteworthy. Studies have demonstrated their effectiveness in lowering serum uric acid levels.[158] In an investigation on the effect of empagliflozin therapy on heart failure, significant interactions were observed between empagliflozin treatment and baseline serum uric acid levels, affecting cardiovascular and all-cause mortality.[159] Additionally, SGLT2 inhibitors have been shown to reduce the risk of incident gout and acute gouty arthritis flares.[159][160] 

Table

Table 7. Urate-Lowering Drugs and Mechanisms .

Table reference [157]

Table

Table 9. Urate-Increasing Drugs and Mechanisms .

Table reference [157]

Differential Diagnosis

The differential diagnosis for an acute gout flare includes the following:

• Calcium pyrophosphate crystal deposition disease
• Basic calcium phosphate crystal disease
• Septic arthritis (crystal arthritis and septic arthritis may coexist) [88]
• Osteoarthritis 
• Psoriatic arthritis
• Cellulitis
• Trauma

The differential diagnosis for tophaceous gout includes:

• Dactylitis
• Rheumatoid arthritis (primarily when associated with rheumatoid nodules)
• Osteomyelitis

Prognosis

The prognosis of gout varies based on the individual comorbidities. Many patients with gout die prematurely, even if their flares are well-controlled by diet and medication. OSA is causally linked to hyperuricemia but is not an independent primary cause of gout. Those experiencing symptoms early in life often present with more severe disease. Without lifestyle modifications, recurrent flare-ups are common. 

Complications

Complications of gout are diverse and may encompass various systemic issues, including the following:

• Skeletal complications

  • Tophi
  • Joint deformity
  • Osteoarthritis
  • Bone loss

• Urological Complications

  • Urate nephropathy
  • Nephrolithiasis

• Ocular Complications

  • Conjunctivitis
  • Uveitis
  • Scleritis [161]

Deterrence and Patient Education

Patients should be educated about lifestyle modifications and strategies to reduce the risk of gout flares and the condition's progression. Important points to discuss with patients include:

• Lifestyle changes are encouraged for patients with gout, including weight loss, limiting alcohol consumption, and avoiding certain foods. While these changes can significantly complement medical therapy, they may not always be sufficient to manage or reverse gout effectively.

• Weight gain and increased adiposity are risk factors for gout. In individuals with established gout who are overweight, weight loss is likely beneficial, leading to reductions in serum urate and alleviation of gout symptoms.[162][163]

• The optimal diet composition for managing gout includes adequate protein intake, especially from plant sources and low-fat dairy sources, while reducing consumption of animal sources high in purine, such as shellfish or red meat. Decreasing saturated fat intake and replacing simple sugars with complex carbohydrates is essential.

• Avoiding or significantly reducing the consumption of sugar-sweetened juices, alcoholic beverages, and drinks containing high-fructose corn syrup is advisable.

Pearls and Other Issues

Key facts to keep in mind about gout include the following:

• Caused by deposition of MSU crystals due to hyperuricemia 

• Hyperuricemia is defined as serum uric acid >6.8 mg/dL

• Most commonly involves the first metatarsophalangeal joint (podagra)

• Crystals are needle-shaped and negatively birefringent under polarized light

• Risk factors include renal failure, thiazide and loop diuretics, obesity, alcohol use, excessive red meat consumption, and seafood intake, especially shellfish

• Can be due to underexcretion (most common) or overproduction of uric acid

• Overproduction causes include Lesch-Nyhan syndrome, tumor lysis syndrome, and myeloproliferative disorders

• Acute attacks treated with NSAIDs (indomethacin), colchicine, or corticosteroids

• Colchicine inhibits microtubule formation and neutrophil chemotaxis

• Chronic management includes allopurinol or febuxostat (xanthine oxidase inhibitors)

• Probenecid increases uric acid excretion but is contraindicated in patients with renal stones

• Pegloticase is a recombinant uricase used for refractory cases. It is an infusion and often requires concomitant immunosuppressive agents to prevent anti-drug antibody formation

• Tophi are chalky deposits of urate crystals seen in chronic gout

• For patients with contraindication to NSAIDs, Glucocorticoids, or colchicine, a short-acting IL-1 inhibitor, like anakinra, may be used for the management of acute gout flare

Enhancing Healthcare Team Outcomes

Most patients with gout have associated comorbidities. The prevalence of gout is significantly higher in individuals with chronic conditions such as hypertension, CKD, diabetes mellitus, obesity, CHF, and prior myocardial infarction. These comorbidities influence gout severity and therapeutic decision-making.[164]

Healthcare providers should be proficient in recognizing classic gout presentations and maintain a low threshold for arthrocentesis when the diagnosis is uncertain. Early joint aspiration is crucial to exclude septic arthritis.

Effective gout management requires an interprofessional approach. Clinicians must promptly identify gout, differentiate it from septic arthritis and other causes of acute monoarthritis, and determine when subspecialty input is required. Comorbidities should guide medication selection, dosing, and monitoring, especially when using NSAIDs, colchicine, corticosteroids, or urate-lowering therapy. Rheumatology referral should be considered in the following situations:

• Unclear joint pain etiology with hyperuricemia
• Unclear etiology despite a normal serum urate level
• Renal impairment limiting medication choices
• Inadequate response to xanthine oxidase inhibitor therapy
• Multiple medication intolerances
• Refractory or tophaceous gout [96]

Pharmacists and nurses play essential roles in reinforcing medication adherence, performing medication reconciliation, verifying appropriate dosing, and advising on alternative agents if first-line therapies fail or are contraindicated. Dietitians support management by counseling patients on weight control, reducing alcohol intake, and limiting purine-rich foods.

Coordinated communication among physicians, advanced practice providers, nurses, dietitians, and pharmacists improves patient education and reduces gout flares by promoting adherence to lifestyle modifications and pharmacologic therapy. An interprofessional team with clear, ongoing communication is essential for reducing gout morbidity, optimizing treatment selection, and achieving favorable long-term outcomes.

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Disclosure: Sharika Menon declares no relevant financial relationships with ineligible companies.

Disclosure: Manjeera Rednam declares no relevant financial relationships with ineligible companies.

Disclosure: Rahul Gujarathi declares no relevant financial relationships with ineligible companies.

Disclosure: Lewena Maher declares no relevant financial relationships with ineligible companies.