Cachexia and Infectious Diseases

Malnutrition, particularly that related to micronu-trients (vitamins, trace minerals, essential amino acids, polyunsaturated fatty acids), is certainly one of the most easily preventable causes of death and disability. The 1995 World Health Organization (WHO) bulletin shows population-attributable risk for child deaths in 52 developing countries due to interaction between malnutrition and infectious disorders [16].

Malnutrition is a common complication of HIV infection and plays a significant and independent role in its morbidity and mortality. Malnutrition was one of the earliest complications of AIDS to be recognised and has been one of the most common initial AIDS-defining diagnoses to be reported to public health authorities [1]. The earliest studies of nutritional status in AIDS patients, performed between

1981 and 1983, were determined in hospitalised patients [17]. Weight loss to an average of 80% of ideal weight was found in this population. Evidence of protein deficiency was documented by demonstrating deficiencies in serum proteins (transferrin, albu-min),haemoglobin, and by muscle wasting (midarm circumference). Several other studies also reported a high prevalence of severe weight loss in AIDS patients at the time of hospital admission.

The results of formal nutritional assessments in HIV infection, using high-precision techniques, were first reported in 1985 [18]. In a cross-sectional study, body cell mass as total body potassium content, fat content, and body water volumes (total body water, intracellular water and extracellular water), were measured in hospitalised, clinically ill AIDS patients and compared to results in normal controls. The AIDS patients averaged 82% of ideal body weight. However, the body cell mass was depleted disproportionately and was only 68% as compared to control. The magnitude of depletion of body cell mass was striking, since the body fat content was not severely depressed, at least in male subjects. The women studied had equivalent depletion of body cell mass as men, but were much more depleted of fat. This finding was confirmed in later studies performed in the USA and Africa [19, 20]. Other studies have concentrated on the body's protein status and have demonstrated that malnutrition is accompanied by depletion of nitrogen, which is directly related to protein content. Approximately one half of the weight difference between HIV-infected and control men could be ascribed to differences in skeletal muscle mass.

The cross-sectional studies described above have provided the field with a point of reference for over a decade. However, it is important to note that these studies were performed in the pre-zidovudine era, at which time the treatment of many complications of HIV disease was rudimentary. These reports document the natural history of untreated HIV infection and AIDS. While the findings may still reflect the nutritional consequences of HIV infection in much of the world, they may be less accurate in the USA, Europe and Australia. More recent studies have shown a relatively greater loss of fat than early studies, and lesser depletion of body cell mass [1].

Other studies have demonstrated that depletion of body cell mass may precede the progression to AIDS, suggesting that cause of the depletion may be related to the underlying HIV infection, rather than to an opportunistic infection [21]. Clinical stability is associated with nutritional stability [22].

Weight loss can be episodic and related to an acute event, often a specific disease complication [23].

Malnutrition in children is manifested as growth failure; a decrease in the rate of increase in linear height [24].

Most opportunistic infections and many lymphomas in AIDS patients are accompanied by cachexia. In such patients, weight loss is rapid (3-5 pounds per week or 5% per month). While the metabolic rate is extremely elevated,food intake is diminished. There is often extreme weakness and lethargy.

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