Severe Peripheral Neuropathy after Exposure to Monosodium Methyl Arsonate

Abstract

A case of severe peripheral neuropathy after several days of exposure to a pesticide spray containing monosodium methyl arsonate (MSMA) is reported. The clinical manifestations of symmetrical peripheral neuropathy with stocking-glove sensory deficit, decreased position sense, decreased and absent deep tendon reflexes, and muscle wasting are consistent with those described in other cases of arsenic intoxication. The anemia, leukopenia, and bone marrow changes of dyserythropoiesis in this case are also similar to those previously described with arsenic intoxication. The authors discuss the possible contribution of toxicity from exposure to other pesticides.

Peripheral neuropathy resulting from arsenic intoxication has been extensively reported in the literature [1–3]. Most of the cases have resulted from ingestion of pesticides, medicinals, or contaminated food and beverages containing inorganic arsenic compounds. Some of the reported cases have probably resulted from direct skin contact with inorganic arsenic sprays and dusts [3]. Peripheral neuropathy resulting from methylated arsenic compounds, however, has not been well described. Cacodyl [(CH₃)₂AsAs(CH₃)₂] and sodium cacodylate [Na(CH₃)₂A_sO₂] have been classified as inorganic arsenicals because their toxicity is related to conversion in the body to arsenous acid [4]. Information on the human toxicity from another methylated arsenic compound, monosodium methyl arsonate (MSMA), is lacking. However, the following case report describes the evolution of a peripheral neuropathy in a farm worker who had skin contact with MSMA.