Methylmercury Poisoning in Canadian Indians — The Elusive Diagnosis

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Abstract
A WHO Expert Committee has concluded that symptoms of methylmercury poisoning may appear at blood concentrations of 200-500 ng Hg/ml. Blood levels in this range were found in several Indian and Inuit communities in Canada. The syndrome of severe methylmercury poisoning (Hunter-Russell syndrome) is well described. Diagnosis of less severe cases is difficult. The problems of diagnosis currently being encountered are discussed and are illustrated by the case of an individual who had 1 of the highest blood concentrations (551 ng Hg/ml) ever described in fish-eating populations outside of the outbreaks in Minamata and Niigata in Japan. Although Hg concentrations in brain were estimated to have been in the symptomatic range at least once in the 2 yr prior to his death, neurohistological examination was normal. Detailed examination by 2 teams of neurologists revealed effects that may be associated with methylmercury poisoning, but a definitive diagnosis remained elusive.