Epidemiology of tropical nutritional neuropathy in Nigerians

Nigerian nutritional ataxic neuropathy comprises panmyelopathy, bilateral optic atrophy, sensorineural deafness and polyneuropathy. In a third of the patients, mucocutaneous evidence of malnutrition is present. The disease occurs in high prevalence in the areas of Nigeria where cassava is most intensely cultivated. Cassava contains a cyanogenetic glycoside, from which hydrocyanic acid is released on hydrolysis. The sex incidence is equal. It is a disease of the poor who subsist entirely on culinary derivatives of cassava. It has a peak prevalence in the 4th to 6th decades. In 41% of 320 patients studied, a positive history that someone else in the household or family suffered from the disease was obtained. In familial cases, 50% are conjugal. There is biochemical evidence of increased exposure to cyanide in ataxic families. There is no evidence so far of a genetically determined predisposition to the disease. Field surveys in 2 villages in an endemic area, and one village in a non-endemic area, showed a positive correlation between the prevalence of the disease and consumption of cassava meals and biochemical evidence of chronic cyanide intoxication. The prevalence rate of the disease in the endemic foci is 18 to 26 per thousand of the population, with a peak prevalence rate of 80 per 1000 in the 6th decade. Cassava processors and farmers who grow and handle cassava may be at special risk. Goitre is not uncommon in patients and may be related to inhibition of iodine uptake by the thyroid due to high concentration of plasma thiocyanate (a detoxication product of cyanide). The epidemiological data support the hypothesis that in Nigerians, chronic cyanide intoxication of dietary origin is the most important factor in the aetiology of ataxic neuropathy. The main source of the cyanide is cassava.