The literature is too large to review here, but excellent critiques have been provided by Winick, Birchfield and coworkers, Latham, and Dodge and colleagues. In contrast to the devastating effect of protein-calorie malnutrition body growth, brain weight is only slightly reduced. Nevertheless, on the basis of experiments in dogs, pigs, and rats, it is evident that prenatal and early postnatal malnutrition retards cellular proliferation in the brain. All cells are affected, including oligodendroglia, with a proportional reduction in myelin. Also, the process of dendritic branching may be retarded by early malnutrition. A limited number of studies in humans suggest that protein-calorie malnutrition has a similar effect on the brain during the first 8 months of life. In animals, varying degrees of recovery from the effects of early malnutrition are possible if normal nutrition is reestablished during the vulnerable periods. Presumably this is true for humans as well, although proof is difficult to obtain. In every series of severely undernourished infants and young children who have been observed for a period of many years, a variable proportion has been developmentally delayed to a modest degree; the majority recovers, however (Galler). Unfortunately, the neurologic and intellectual consequences of protein-calorie malnutrition have defied accurate assessment because of the difficulty of isolating the effects of severe malnutrition from those of infection, social deprivation, genetic mechanisms, and other factors.
Nutritional Deficiencies Secondary to Malabsorption
The vitamins known to be essential to the normal functioning of the central and peripheral nervous systems cannot be synthesized by the human organism. Each is ingested as an essential part of the normal diet and absorbed in certain regions of the gastrointestinal tract. Impairment or failure of absorption caused by diseases of the gastrointestinal tract gives rise to several malabsorption syndromes, some of which have already been referred to, for example, malabsorptive vitamin E deficiency. In these diseases, the site of the block in transport from the intestinal lumen varies; it may be at the surface of the enterocytes or at their interface with the lymphatic channels and portal capillaries.
Table 40-2, which is modified from Pallis and Lewis, lists the main malabsorptive diseases and their relationships to the intestinal abnormalities. Of all these diseases, celiac sprue (gluten enteropathy) is the most common. The neurologic complications of this disorder, in our experience, have taken the form of a symmetrical, predominantly sensory polyneuropathy, as described in Chap. 43. However, other complications have been described, notably a progressive cerebellar syndrome with cortical, dentatal, and olivary cell loss. The cerebellar changes may be coupled with a symmetrical demyelination of the posterior columns, producing a spinocerebellar disorder similar to that of vitamin E deficiency, but in the latter case, vitamin E supplementation has no consistent effect. Others have remarked on a high incidence of depression and other psychiatric disturbances in adult patients with celiac sprue, as also discussed in Chap. 39. Unexplained seizures are also said to occur.
Polyneuropathy and SCD of the spinal cord manifesting themselves many years after gastrectomy are encountered only rarely. The neurology of gastrointestinal disease has also been reviewed by Perkin and Murray-Lyon.
INHERITED VITAMIN-RESPONSIVE NEUROLOGIC DISEASES (SEE TABLE 40-3 AND CHAP. 36)