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Wernicke encephalopathy in infants.

Our knowledge of cellular biochemistry has increased enormously in recent decades, but the effects of profound reduction of single dietary constituents on function and stability of nerve cells in selected areas of the brain remain puzzling. In this issue of the Journal of Neuro-Ophthalmology, Kesler et al. (1) report the clinical features of three of twenty patients who developed Wernicke encephalopathy after being fed a soy-based thiamine-deficient diet during the first months of life. Apathy, vomiting, and abnormal eye movements brought them to medical attention and helped make the diagnosis. Although isolated cases have been reported previously in infants fed thiamine-deficient formulas by oral or parenteral routes (2,3,4), this is the first epidemic of thiamine deficiency in human infants resulting from the ingestion of a commercial formula. Phosphorylated esters of thiamine are stored in tissue and act as coenzymes in the function of major oxidative enzymes such as pyruvate, alpha-ketoglutarate dehydrogenase, and transketolase. A severe deficiency of thiamine in an otherwise satisfactory diet initially produces restricted damage in the nervous system. The signs of Wernicke encephalopathy predominate in the neonate. On the other hand, where infants suffer from thiamine deficiency associated with severe protein-calorie malnutrition, as in the Karen in southeast Asia, infantile beri-beri is a major cause of death (5). At least two factors could be responsible for this difference in clinical presentations. The diet of Karen dwellers contains foods that have considerable thiaminase, which is not found in formulas. Commercial formulas, on the other hand, contain much higher amounts of glucose, which is known to worsen the CNS effects of thiamine deficiency in the rat (6). This epidemic raises again two interesting questions in regard to thiamine deficiency. First, why does a thiamine-deficient diet preferentially affect neurons in particular areas of the nervous system such as the putamen, parts of the thalamus, and the periaqueductal gray matter? In neonates, these structures have high rates of oxidative metabolism which could make them more vulnerable? Thiamine turnover is also higher in these areas (7). Second, why did these children have no neurologic signs for up to six months on this thiamine-deficient diet, after which there was rapid progression and, in one case, lack of recovery with treatment? Thiamine is preferentially concentrated in the fetus by the placenta (8). Stores in the neonate should be adequate at birth. We can presume that a gradual decrease in tissue stores of thiamine and its esters after birth in infants placed on a low thiamine diet could result in a decrease in oxidative metabolism and mitochondrial function which progressively interferes with the normal activity of neurons and endothelial cells. As these cells begin to die, there is an influx of microglia and eventually macrophages and a rapid accumulation of toxic substances such as glutamate and elements capable of creating rapid oxidative damage to the cell that would accelerate cell death. Once cell death is extensive enough, there may be no recovery after treatment with thiamine (9). Kesler et al. (1) note that only 20 of 3,500 babies fed this diet became ill. They suggest that these may have been infants whose mothers had low stores of thiamine during