Chronic cyanide poisoning in relation to blindness and tropical neuropathy.

Within a group of 20 patients showing optic atrophy and macula degeneration, 14 patients could be examined for neurological and audiometric defects. In 6 patients neurological signs and symptoms were observed. Nine patients reported loss of hearing and in 3 of them a severe perceptive deafness was seen in the audiogram. In 3 of the 14 patients a combination of severe neurologic and audiologic symptoms developed and in two of them a high thiocyanate concentration in serum was observed. The occurrence of perceptive deafness and posterior column sensory loss in the lower extremities in four of the patients made the diagnosis of polyneuropathy the most plausible. Although a similarity to chronic myelopathies caused by nutritional cyanide poisoning cannot be denied, the mean thiocyanate concentration in plasma 24 mumol/L (1.39 mg/L), and the cyanide levels in the blood 0.09 mumol/L (2.3 micrograms/L) were substantially lower than those found in other individuals during periods of extreme drought in which food only consisted of the bitter variety of cassava. The role of cyanide in the etiopathology of this polyneuropathy is unknown.