An epidemic of optic neuropathy in Tanzania: characterization of the visual disorder and associated peripheral neuropathy.

An epidemic of subacute bilateral visual failure has affected large numbers of teenagers and young adult Africans in coastal Tanzania since 1988. Previous work had indicated that many patients had sensory symptoms, but the nature of the neurological involvement was uncertain. The primary objective of this study was to characterize the accompanying neurological disorder. Furthermore, the nature of the visual loss was uncertain from previous reports as both retinopathy and optic neuropathy had been suggested. Full ophthalmic and neurological examinations were carried out at the Muhimbili University Hospital in Dar es Salaam. Nerve conduction studies, pattern electro-retinograms and cortical visually evoked responses and colour contrast sensitivity tests were carried out. Thirty eight young Africans and 12 controls were included in the study. The characteristic fundus picture was symmetrical temporal optic atrophy, and thinning of the caeco-central nerve fibre layer. Fluorescein angiography was normal. The electrophysiological and colour contrast sensitivity tests confirmed optic neuropathy in the majority of cases but primary retinal involvement was indicated in some. Neurological examination and nerve conduction measurements showed evidence of a peripheral neuropathy in 47% of the patients. The peripheral neuropathy is likely to have involved large fibres (from the nerve conduction studies) but the symptoms suggest small fibre loss also. 42% had developed hearing loss. Urinary thiocyanate levels were uniformly low. Serum was negative for antibodies to HTLV-1. DNA analysis from three cases was negative for three known mutations associated with Leber's hereditary optic atrophy (11778, 3460 and 14484). This entity, occurring predominantly in a young age group, does not correspond closely to other tropical neurological syndromes previously described from East Africa although it is clinically very similar to Strachan's syndrome (originally described in the Caribbean and more recently in prisoners of war) and also to an epidemic of optic and peripheral neuropathy that has recently occurred in Cuba. The aetiology has not yet been determined. A micronutrient deficiency is likely but has not been established.