As already mentioned, alcoholism is an important factor in the causation of nutritional diseases of the nervous system. Alcohol acts mainly by displacing food in the diet but also by adding carbohydrate calories (alcohol is burned almost entirely as carbohydrates), thus increasing the need for thiamine. There is some evidence as well that alcohol impairs the absorption of thiamine and other vitamins from the gastrointestinal tract.
In infants and young children, a reduction in protein and caloric intake (so-called protein-calorie malnutrition) has a devastating effect on body growth. Whether or not protein-calorie malnutrition also hinders the growth of the brain, with consequent effects on intellectual and behavioral development, cannot be answered as readily. The data bearing on this matter are discussed in the last part of this chapter.
Some comments will also be made in this chapter about the rare hereditary vitamin-responsive diseases. There are several distinctive neurologic disorders in which nutritional deficiency may partly contribute are discussed in other chapters. These include “alcoholic” cerebellar degeneration (Chap. 41) and central pontine and extrapontine myelinolysis (Chap. 39). Deficiencies of trace elements, because of their rarity, are not discussed; only iodine deficiency (cretinism) is of much importance in humans, and it was discussed in Chap. 39 on acquired metabolic diseases.
Wernicke disease and the Korsakoff amnesic state are common neurologic disorders that have been recognized since the 1880s. Wernicke disease is characterized by nystagmus, abducens and conjugate gaze palsies, ataxia of gait, and confusion. These symptoms develop acutely or subacutely and usually occur in varying combinations. Wernicke disease is specifically the result of a deficiency of thiamine.
The Korsakoff amnesic state (Korsakoff psychosis) is a mental disorder in which retentive memory is impaired out of proportion to all other cognitive functions in an otherwise alert and responsive patient. This amnesic disorder, like Wernicke disease, is most often associated with the thiamine deficiency of alcoholism and malnutrition, but it may be a symptom of various other non-nutritional diseases that have their basis in structural lesions of the medial thalami or the hippocampal portions of the temporal lobes, such as infarction in the territory of branches of the posterior cerebral arteries, hippocampal damage after cardiac arrest, third ventricular tumors, and herpes simplex encephalitis. An almost equivalent type of memory disturbance may also follow acute lesions of the basal septal nuclei of the frontal lobe. Transient impairments of retentive memory of the Korsakoff type may be the salient manifestations of temporal lobe epilepsy, concussive head injury, and a transient global amnesia. The anatomic basis of the Korsakoff amnesic syndrome is described in Chap. 20.
In the nutritionally deficient patient, Korsakoff amnesia is usually associated with and immediately follows the occurrence of Wernicke disease. For this reason and others elaborated in the following text, the term Wernicke disease or Wernicke encephalopathy is applied to a symptom complex of ophthalmoparesis, nystagmus, ataxia, and an acute apathetic–confusional state. If an enduring defect in learning and memory results, as it often does, the symptom complex is designated as the Wernicke-Korsakoff syndrome.