Thiamine deficiency and the etiology of tropical ataxic neuropathy

Tropical ataxic neuropathy (TAN) is a syndrome characterized by sensory polyneuropathy, sensory ataxia, bilateral optic atrophy and bilateral sensorineural deafness. The syndrome has occurred in endemic form in several African countries, and in epidemic form in Cuba. In endemic communities, the syndrome has a high prevalence and a demonstrated risk for high mortality. Despite several studies aimed at elucidating the etiological mechanisms of TAN, the etiology has remained unknown more than five decades after its original description. Chronic cyanide intoxication from a monotonous diet of cassava was long thought to be the major etiological factor, but there has been no evidence of a causal association. Vitamin deficiencies were thought to play little or no role in the pathogenesis of TAN. Evidence from the literature implicating chronic thiamine deficiency in the etiology of TAN is presented in this communication. This includes evidence of abnormal pyruvate metabolism reversed by thiamine in patients with TAN, evidence from erythrocyte transketolase activity indicating significant thiamine deficiency in patients with TAN compared to controls, and a placebo-controlled trial of therapeutic doses of thiamine which showed a clinically dramatic and statistically significant improvement in ataxia. A long-term thiamine supplementation program for susceptible individuals in endemic areas may be effective in the control and eventual eradication of the disease.