Neuropathy after organophosphorus compounds poisoning

Low-level exposures to organophosphorus esters and peripheral nerve function

This review evaluates the epidemiological and clinical evidence linking low-level and prolonged exposures to organophosphorus esters, used as insecticides or nerve agents, to peripheral nerve dysfunction. The clinical effects of large doses of these chemicals-including the cholinergic syndrome, the intermediate syndrome, and the delayed polyneuropathy-are all well established and are summarized. Based on these clinical observations and experimental studies, dose-effect relationships indicate that peripheral neuropathy always develops after cholinergic toxicity. However, several studies have suggested that this relationship may be different after low-level prolonged exposures, as, for instance, those experienced by Gulf War veterans and British sheep farmers, thereby leading to the development of peripheral neuropathy without preceding cholinergic toxicity. A critical assessment of these studies, involving subjects with either current or past exposures, indicates that changes in peripheral nerve function were mild, inconsistent, and unexplained and that most studies lack exposure data. Suggestions made about individual hypersusceptibility to delayed polyneuropathy lack support. It is concluded that there is no evidence of peripheral nerve dysfunction caused by low-level prolonged exposures to organophosphate insecticides or nerve agents.

Biological monitoring for organophosphate-induced delayed polyneuropathy

Certain organophosphate (OP) pesticides cause a delayed polyneuropathy. The two-step initiation mechanism for this toxicity involves the phosphorylation and subsequent 'aging' of a protein in the nervous system called Neuropathy Target Esterase (NTE). The observation of this enzyme activity in peripheral blood lymphocytes led to several studies to verify whether its measurement after OP exposures might be used as a biological monitoring test for the OP-induced delayed polyneuropathy (OPIDP). The evidence, so far, on the use of this biochemical test in man is discussed together with the need for further research.