Definitions

Current SSA guidelines consider FTT to be present when there is a fall in weight to below the 3^rd percentile or to less than 75% of median weight-for-height or age in children under two years old. There must be no underlying medical disorder, and growth failure should last, or be expected to last, for at least twelve months. These guidelines are to be updated and the purpose of this review of the literature was to generate an evidence base to assist the SSA in revising its disability policy with regard to children who are failing to thrive.

Most clinicians make a diagnosis of FTT when children's growth in weight and/or in height fails to increase as expected for their age. Operationally this is frequently defined as a crossing of two or more standard percentile lines in a standard growth chart. Other clinicians use a definition of FTT that can be assessed without access to growth charts, or that can be assessed at a single point in time. These definitions include children who are persistently at or below the third or fifth percentile for weight, or less than 80 percent of median weight-for-height or weight-for-age.

Other definitions are used commonly in the professional literature such as height-for-weight <3^rd percentile; weight-for-age less than 3^rd or 5^th percentile or less than 80 percent of median for age; weight-for-height <10^th percentile; and weight-for-age more than 2 standard deviations below the mean for age. Because of inconsistent definitions it is hard to make comparisons among the various investigative approaches to this syndrome.

Earlier research attempted to distinguish FTT that resulted from a known organic disease process from the more common circumstance in which the specific cause for the growth failure is unknown. This distinction is no longer considered useful. Instead, current data suggest that organic and non-organic causes and effects are intertwined in most affected children. Therefore, this review will not use the terms organic or non-organic FTT. Parenthetically, the SSA definition is a reflection of an outdated conceptual model and should be reconsidered. It does not reflect the current thinking, which is that failure to thrive is a complex interaction of medical, nutritional developmental, and social factors which all can contribute to disability.

Depending on the definition used and demographics of the population sampled, the reported prevalence of FTT ranges from 1.3% to 20. 9% (Reilly and Skuse, 1994). Previous reports have estimated its prevalence among hospitalized children to be from 1 to 5% (Zenel, Jr., 1997). It is difficult to estimate the true prevalence of FTT due to the variety of diagnostic criteria used to identify it, and because most children are not hospitalized.

Cross sectional data from the developing world suggest that weight for age is a potent predictor of mortality, while height for age, which reflects duration of insult, correlates with developmental outcome (Wright, Ashenburg, and Whitaker, 1994). Further research is needed to define which criteria are the best predictors of medical and cognitive sequelae of FTT in the United States.

Causes and Effects of FTT

The underlying cause of FTT is always insufficient usable nutrition. This may occur when sufficient nutrients are not available to the child as a result of social or environmental causes that prevent parents from obtaining, preparing, or offering age-appropriate foods to the child. This growth failure often includes concurrent and potentially persistent disability. This syndrome of under-nutrition, previously termed “non-organic FTT” is recognized as a multifaceted disease. Because of this, the world's literature on the disabilities of poorly nourished children in developing as well as developed countries becomes relevant to the discussion of disability arising from FTT even in the USA.

In addition, almost any serious pediatric illness can result in FTT. There are three basic mechanisms for this phenomenon: (1) insufficient nutrition is available to the child because of the child's inability to feed properly, e.g. severe neurological dysfunction, gastroesophageal reflux; cleft palate; (2) nutrition is adequate but inadequately absorbed and/or utilized (malabsorption syndromes); or (3) the disease process creates added metabolic requirements, e.g. asthma, cardiac failure, thyroiditis. It is not uncommon for FTT to be the first clue to an active disease process, which has not yet manifested itself in specific symptomatology.

Whatever its multidimensional causes, FTT affects growing children in many important ways. Severe malnutrition has been shown to cause permanent structural aberrations in the central nervous system. Even mild malnutrition not sufficient to cause dramatic growth failure has been associated with aberrations in neural transmitters and CNS functions with the detectable impairments reflected in a range of disabilities. In addition, FTT is closely linked with infectious disease. Children who are undernourished (of which FTT is an indicator) consistently have been found to have significant and profound changes in cell-mediated immunity, complement levels, and opsonization (vi) that lead to susceptibility to various infections. FTT is associated with persistently small stature. Severe FTT are associated with multiple physiological derangement in cardiovascular and gastrointestinal functioning.

The review that follows attempts to determine the value of the symptom complex of FTT as a marker for basic physiological derangements that might otherwise be either undetectable or non-existent. That is, we are interested in how often a child's failure to grow occurs prior to or coincident with another potentially disabling childhood condition. We do not consider the co-occurrence of FTT with known chronic health conditions that are already regarded as disabling e.g. cystic fibrosis, congenital heart disease, or celiac disease, although undernutrition is known to exacerbate the severity and course of these and other pediatric health conditions. The question that directed this review is: Among children defined by investigators as failing to thrive or to grow adequately, what evidence exists that they have a concurrent disability, or will have one within six months. The definition of disability used for this investigation is an operational one; “the presence of a medically determinable physical or mental impairment that causes marked and severe functional limitations and that is expected to last for 12 months or more”.

Association of FTT with Immunological Functioning

Malnutrition severe enough to produce growth failure also impairs immuno-competence, particularly cell-mediated immunity, and diminishes production of complement and secretory IgA. Recurring otitis media, gastrointestinal and respiratory infections are more common among children who fail to thrive than among well-nourished children of the same age.

Children who are not thriving are often trapped in an infection-malnutrition cycle. With each illness, the child's appetite and nutrient intake decrease while nutrient requirements increase as a result of fever, diarrhea, and vomiting. In settings in which nutrient intake is already marginal, even when the child is well, cumulative nutritional deficits occur, leaving the child increasingly vulnerable to more severe and prolonged infections and even less adequate growth. Even in developed countries, malnourished children succumb more often than thriving children to fulminating infections. The more common syndrome of recurrent low-grade infections interferes with both physiologic and psychological processes of childhood.

Association of FTT with Neurological Functioning

Insufficient nutrition is associated with perturbations of neurotransmitters and impaired exploration and learning, even before growth is affected. By the time a child has experienced under-nutrition for a long enough period to be identified as “failing to thrive” there have been many “silent” episodes of impaired learning and interaction which cumulatively produces lasting disabilities in cognition and social behavior. Evidence from developing countries of the dire effects of protein-calorie malnutrition on intelligence and social behavior have shed light on the mechanisms that result in impairments at even far less extreme levels of malnutrition, such as those found in the US with alarmingly high prevalence.

These mechanisms account for the most significant persistent physiological derangement that is associated with FTT, namely that of central nervous system function. The majority of available data documents both delayed development and disordered behavior and affect in children at the time of diagnosis of FTT/malnutrition. This is particularly true of children who come to medical attention because of their growth failure, but also to a lesser extent of children identified only in epidemiologic surveys. The majority of studies of clinically diagnosed cases of FTT show reproducible developmental impairments. Various aspects of school achievement, memory, and attentional functions seem to suffer lasting impairment. The effects on the CNS are both structural with impaired myelinization and dendritic arborization, and functional in terms of altered neurotransmitter synthesis.

Growth Abnormalities

Growth failure is the most obvious and persistent symptom and sequelae of FTT. Depending on the age of the child when growth failure occurred and the length of time it existed before it was corrected, short stature almost always persists even after the child is once again adequately nourished.

Other Associated Health Problems

Elevated lead levels correlate with impaired growth, even in the 5 to 35 mg/dl range. Here too, a negative cycle develops. Nutritional deficiencies of iron and calcium enhance the absorption of lead and other heavy metals. As lead levels rise, constipation, abdominal pain, and anorexia occur, leading to even less adequate dietary intake. In a recent study, 16% of children with FTT had lead levels high enough to warrant chelation.

Summary

Some of the disabilities created and/or maintained by malnutrition/FTT are restored with nutritional rehabilitation, such as immune, gastrointestinal, and cardiac function, and weight for height. On the other hand, other disabilities are permanent; there are persistent impairments in stature, cognition, attention, and behavior.