Neurologic disorders caused by a lack or excess of these fat-soluble vitamins have been reported, but they are rare. Vitamin A deficiency sometimes occurs with malabsorption syndromes, causing impairment of vision. Excess of vitamin A may provoke the syndrome of intracranial hypertension, or pseudotumor cerebri (see Chap. 29). Vitamin D deficiency is associated with hypoparathyroidism or a malabsorption state that leads to hypocalcemia, proximal muscle weakness, and rickets.
Several related conditions of nutritional deficiency overlap in their presentations and have in common an uncertainty as to the primary cause. In all likelihood, there is a combination of factors, perhaps conditioned by genetic susceptibility. Here we refer especially to a syndrome of spastic ataxia, blindness, and a severe painful neuropathy with glossitis but there are other derivative syndromes that we discuss in this section.
This syndrome is observed occasionally in nutritionally depleted alcoholics. The main clinical signs are spastic weakness of the legs, with absent abdominal and increased tendon reflexes, clonus, extensor plantar responses, and a loss of position and vibratory senses. In our experience, this syndrome has usually been associated with other nutritional disorders such as Wernicke disease and peripheral and optic neuropathy. In prisoner-of-war camps, the “spastic syndrome” was observed in association with mental and emotional changes and dimness of vision, and at times with widespread muscular rigidity, confusion, coma, and death. The latter syndrome has never been studied pathologically, so that it is impossible to state whether the lesions are the same as or different from those of pellagra or from Strachan syndrome, described further on.
The syndromes of tropical spastic paraparesis and of lathyrism, another form of spastic paraplegia common in India and certain parts of Africa, were for many years suspected of being nutritional in origin but are now known to be caused by a virus and a toxin, respectively. These and other types of tropical spastic paraplegia are discussed in greater detail with the spinal cord diseases (see Chap. 42). A chronic tropical disease of the peripheral nerves, called “ataxic neuropathy of Nigeria,” has been attributed to the ingestion of inadequately detoxified cassava (Osuntokun) that contains cyanide. Another form of spastic ataxia, called “konzo,” has been attributed to the production of cyanide by an ingested toxic glycoside in individuals who are protein deficient. The differential diagnosis of progressive spastic ataxia is quite broad and includes multiple sclerosis.
Nutritional Optic and Peripheral Neuropathy, “Tobacco–Alcohol Amblyopia,” and Strachan Syndrome (See Also Chap. 12)
These terms refer to a characteristic form of visual impairment that results from nutritional deficiency. The defect in vision is the result of a lesion of the optic nerves, more or less confined to the region of the papillomacular bundle. Typically, the patient complains of dimness or blurring of vision for near and distant objects, evolving gradually over a period of several days or weeks. Examination discloses a reduction in visual acuity because of the presence of central or centrocecal scotomata, which are larger for colored than for white test objects. Pallor of the temporal portion of the optic disc is observed in some cases. These abnormalities are bilateral and roughly symmetrical and, if untreated, may progress to blindness and irreversible optic atrophy. With normal diet and vitamin supplements improvement occurs in almost all cases but the most chronic ones; the degree of recovery depends on the severity of the amblyopia and particularly on its duration before therapy is instituted.