Continuing Education Activity

Hypnic headache is a rare primary headache disorder that typically presents in older adults and is characterized by a headache that consistently awakens the patient from sleep and lasts for a short duration, from 15 minutes to 4 hours. Because of the circadian pattern, this condition is often called the clockwise or alarm-clock headache. Hypnic headache accounts for fewer than 1% of headaches. Because many other conditions can mimic this type of headache, excluding other serious or untreated causes of headaches that disturb sleep is essential. The evaluation should exclude more common disorders such as obstructive sleep apnea and structural abnormalities.

This activity reviews the recognition, diagnosis, and evaluation of nocturnal headaches and the management of hypnic headaches. The material equips healthcare professionals with practical tools to accurately identify and treat this disorder. The role of the interprofessional health care team is emphasized, as further testing, such as sleep studies and neuroimaging, may be warranted. Because patients often first present to a primary care clinician or the emergency department with nocturnal headaches, recognizing the classic features of hypnic headache supports timely diagnosis and effective treatment, intending to improve patient outcomes.

Objectives:

• Identify the typical presentation and diagnostic criteria of hypnic headache.
• Determine the appropriate evaluation of hypnic headaches and investigate other causes of nocturnal and secondary headaches. 
• Select appropriate pharmacologic treatments and preventive measures for patients with hypnic headache. 
• Collaborate with the interprofessional team, including the emergency department and primary care clinician or neurologist, to enhance the delivery of care and improve outcomes for patients with hypnic headache.

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Introduction

Headache disorders are among the leading causes of morbidity and years lived with disability worldwide.[1][2] Headaches have been classified into various categories based on the International Classification of Headache Disorders Criteria.[3] Hypnic headache (HH) is a rare, primary headache disorder that occurs exclusively during sleep, usually simultaneously each night. Previously, HH was referred to as "the clockwise headache" or "alarm clock headache." The International Classification of Headache Disorders, 3rd ed classifies hypnic headache as a primary headache disorder.[4]

HH is characterized by attacks of dull headache that typically present after age 50, occur at least 10 times per month, and occur during sleep without associated autonomic symptoms. The attacks awaken the patient from sleep and usually last 15 minutes to 4 hours after waking.[5] Hypnic headache is a chronic disorder that can last for many years, but has moderate remission rates with treatment.[6]

Patients with migraine and hypertension are more likely to develop HH. Nearly all patients with HH exhibit motor activity during the attack, such as getting out of bed, eating, drinking, showering, or reading when awakened by the headache. However, the restlessness is less severe than cluster headache and trigeminal autonomic cephalalgias.[7] Other causes of nocturnal headache and secondary headaches should be excluded before confirming a diagnosis of HH.[8]

Etiology

HH is a primary headache disorder with no identifiable etiology that may be associated with changes in the parts of the brain involved in pain, melatonin production, or rapid eye movement sleep. 

Epidemiology

About 0.07% of all patients presenting with headache have HH. Among older adults presenting with headache, 1.4% were diagnosed with HH, according to results from a study in Italy.[7] Recently, results from a French study reported a prevalence of 0.3% to 0.6%.[9]

Pathophysiology

The pathophysiology of HH is unclear. However, the consistent timing of nocturnal attacks suggests hypothalamic circadian rhythm dysfunction.[8] Decreased gray matter volume of the posterior hypothalamus on imaging may be associated with HH.[10] Additionally, the suprachiasmatic nucleus may be involved in the pathophysiology of HH. With age, the number of cells in the suprachiasmatic nucleus decreases significantly, which leads to a decrease in melatonin production, an important regulator of the circadian rhythm. The suprachiasmatic nucleus projects to and receives afferents from the brainstem periaqueductal gray, suggesting the involvement of pain-modulating circuits.[10]

Sleep-disordered breathing is not associated with HH. Furthermore, continuous positive airway pressure and nocturnal oxygen supplementation do not improve symptoms of HH, indicating that hypoxemia or hypercapnia are not associated. HH attacks can occur during rapid eye movement sleep (REM), which may be due to arterial hypertension and low oxygenation. However, more than half of HH attacks occur during non-REM sleep, and HH may happen in both REM and non-REM sleep in the same patient, suggesting no association between HH and a specific sleep stage.[11]

History and Physical

Patients usually describe symptoms of frequent, recurrent headaches occurring exclusively during sleep. HH causes awakening and lasts for up to 4 hours. Characteristic associated neurologic symptoms are typically absent. The formal criteria for HH according to the International Classification of Headache Disorders, 3rd ed, are:

1. Occur only during sleep and cause awakening
2. Occur ≥ 10 days per month for at least 3 months
3. Last ≥ 15 minutes for up to 4 hours after awakening
4. Not accompanied by cranial autonomic symptoms or restlessness

Additionally, the headache should not be caused by another diagnosis.[8]

Other characteristic features of HH include:

• Timing: Headaches usually occur exclusively during sleep, exhibiting circadian rhythmicity.[12]
• Age: While typically described in adults older than 50, HH has been reported in younger patients.[13]
• Gender: The disorder appears to affect women more than men, with a 2:1 ratio.[8]
• Duration: The mean duration of hypnic headache is 115 minutes; however, it can last from 15 minutes to 4 hours.[14]
• Intensity: Usually moderate to severe intensity, with a small percentage of people reporting mild headaches.
• Character: Most commonly dull, but throbbing or pulsating pain may occur. 
• Location: Usually bilateral and diffuse.
• Associated features: These headaches are rarely associated with migrainous (nausea/vomiting, photophobia/phonophobia) or autonomic (lacrimation, conjunctival injection) features.[15]

Evaluation

Evaluation of patients with HH is similar to evaluation for other nocturnal headaches. Secondary causes should be excluded, including malignancy, nocturnal arterial hypertension, nocturnal hypoglycemia, medication overuse or withdrawal, cervicogenic headache, giant cell arteritis, obstructive sleep apnea, and other sleep disorders.[16][17] MRI of the brain can identify structural abnormalities with and without contrast. MRI may also demonstrate grey matter volume reduction in the hypothalamus. An overnight polysomnography study is necessary to exclude obstructive sleep apnea and other sleep disorders. Once any organic cause of the headache has been excluded, the diagnosis is based on the International Classification of Headache Disorders, 3rd ed criteria. 

Treatment / Management

While there is a lack of high-quality clinical data regarding the management of hypnic headaches, the following medications may be beneficial:

• Caffeine: A dose of 40 to 60 mg of caffeine can be helpful in the treatment of HH. Older adults often tolerate caffeine well and do not experience sleep disturbances.[18] Caffeine is frequently used as a first-line abortive treatment, but can also be used preventively before bedtime.[19]
• Lithium: Raskin et al published the first reports on the effectiveness of lithium in treating HH. Several other studies have been published since then, corroborating these findings. The most effective dose is 150 to 600 mg/day, administered in single or divided doses, to achieve a serum level of 0.5 to 1.0 mmol/L. Lithium is highly effective as a preventive therapy for hypnic headache, but has several adverse effects and polypharmacy risks, especially in older adults.
• Indomethacin: Indomethacin is particularly beneficial in patients with hemicranial HH or associated autonomic features. The usual dose is 25 to 150 mg at bedtime. Older adults require regular monitoring for potential adverse effects.[20][21]
• Other agents: Medications with conflicting evidence include tricyclic antidepressants, flunarizine, beta blockers, verapamil, nonsteroidal anti-inflammatory drugs, prednisolone, anticonvulsants, acetazolamide, melatonin, benzodiazepines, pizotifen, and topiramate.[22]
• Emerging therapies: Case reports suggest that onabotulinum toxin A and occipital nerve stimulation may be efficacious, but these interventions carry more complications due to their invasive nature.[23][24][25][26][27]

Differential Diagnosis

The differential diagnoses of HH include other headache disorders that occur during sleep, such as migraine, cluster headache, cervicogenic headache, and short-lasting unilateral neuralgiform headache with conjunctival injection and tearing. Please see StatPearls' companion resource,"Cervicogenic Headache" and "Retinal Migraine Headache," for further information.[28] Important secondary causes of headache, such as brain tumors, obstructive sleep apnea, medication overuse and withdrawal headaches, nocturnal arterial hypertension, and idiopathic intracranial hypertension, should be evaluated. Brain imaging with CT or MRI is usually indicated to exclude structural abnormalities.

Prognosis

Approximately 17% to 40% of patients experience spontaneous remission from HH, while most continue to have chronic symptoms. Up to 53% of patients may develop an episodic course following treatment.[29]

Complications

There are no reported long-term neurologic sequelae associated with HH.[30] 

Deterrence and Patient Education

Because the exact etiology of HH is unclear, prevention can be challenging. Patients should be educated about the benign nature of HH and the use of prophylactic strategies to reduce the frequency of attacks.  

Enhancing Healthcare Team Outcomes

Patients with HH often present with nocturnal, sleep-disrupting headaches that can mimic other conditions such as intracranial tumors, giant cell arteritis, or obstructive sleep apnea. Early recognition and accurate diagnosis lead to timely and appropriate treatment. The care of these patients requires a collaborative, interdisciplinary approach involving neurologists, primary care clinicians, emergency medicine clinicians, nurses, pharmacists, and other healthcare professionals. Each team member can learn to recognize the classic features of HH, enabling initiation of further evaluations and referrals to other healthcare team members for long-term follow-up. HH should be differentiated from other nocturnal headache etiologies, and interdisciplinary team members should understand the necessary evaluation, including sleep studies and neuroimaging.

Once hypnic headache is diagnosed, patient education regarding the prognosis and treatment options is essential for patient-centered care. As hypnic headache primarily presents in older adults, active collaboration with pharmacists and other clinicians can help prevent polypharmacy and medication adverse effects. Ethical principles must guide care decisions, ensuring patients are fully informed of their diagnosis, treatment options, and expected outcomes. The prognosis for hypnic headache remains favorable with proper treatment; however, investigating secondary causes may be critical in the initial setting and in cases of refractory headaches. Coordinated care efforts, from initial diagnosis through follow-up management, enhance patient safety, minimize diagnostic delays, and improve patient satisfaction. Patient-centered decision-making will enhance treatment adherence and overall quality of care for patients with hypnic headache.

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Disclosure: Yasir Al Khalili declares no relevant financial relationships with ineligible companies.

Disclosure: Christopher Tan declares no relevant financial relationships with ineligible companies.

Disclosure: Forshing Lui declares no relevant financial relationships with ineligible companies.