Acetylcholinesterase inhibition and the extrapyramidal syndrome: A review of the neurotoxicity of organophosphate

Organophosphate poisonings are not uncommon, and are the leading cause of d eath in suicide patients in Taiwan. Acute cholinergic crisis caused by the inhibition of synaptic acetylcholinesterase is the major manifestation of o rganophosphate poisoning and may cause death within minutes. Delayed neurot oxicities include intermediate syndrome and delayed polyneuropathy have als o been described. However, these symptoms may not characterize the complete picture of organophosphate poisoning. Among the 633 patients ever admitted to our hospital with organophosphate poisoning, three patients were found exhibiting impermanent neuromuscular dysfunction, including blepharoclonus, oculogyric crisis, intermittent dystonia, rigidity, and tremor with two of them developing mask face, dyskinesia and akathisia later, following acute cholinergic crisis. The symptoms appeared within 4 days with the duration ranging from 25 days to 2 months. Other causes of the extrapyramidal syndro me noted on these patients ha ve been excluded, and we consider the extrapy ramidal syndrome a possible neurotoxic manifestation of organophosphate poi soning, which is transient, needs no treatment, and may be missed because o f the critical condition, in a minority of patients. The mechanism remains to be identified, but may be related to the impediment of the function of a cetylcholinesterase to modify nigrostriatal dopaminergic system, which is i ndependent of hydrolyzing acetylcholine. More detailed observation for orga nophosphate poisoned patients and more studies for the biological functions of acetylcholinesterase including the influence on the nigrostriatal dopam inergic system are needed. (C) 2001 Elsevier Science Inc. All rights reserv ed.