A systematic review on the nerve–muscle electrophysiology in human organophosphorus pesticide exposure

Abstract

This article presents a systematic review of the recent literature on the scientific support of electromyography (EMG) and nerve conduction velocity (NCV) in diagnosing the exposure and toxicity of organophosphorus pesticides (OP). Specifically, this review focused on changes in EMG, NCV, occurrence of intermediate syndrome (IMS), and OP-induced delayed polyneuropathy (OPIDN) in human. All relevant bibliographic databases were searched for human studies using the key words "OP poisoning", "electromyography", "nerve conduction study," and "muscles disorders". IMS usually occurs after an acute cholinergic crisis, while OPIDN occurs after both acute and chronic exposures. Collection of these studies supports that IMS is a neuromuscular junction disorder and can be recorded upon the onset of respiratory failure. Due to heterogeneity of reports on outcomes of interest such as motor NCV and EMG amplitude in acute cases and inability to achieve precise estimation of effect in chronic cases meta-analysis was not helpful to this review. The OPIDN after both acute and low-level prolonged exposures develops peripheral neuropathy without preceding cholinergic toxicity and the progress of changes in EMG and NCV is parallel with the development of IMS and OPIDN. Persistent inhibition of acetylcholinesterase (AChE) is responsible for muscle weakness, but this is not the only factor involved in the incidence of this weakness in IMS or OPIDN suggestive of AChE assay not useful as an index of nerve and muscle impairment. Although several mechanisms for induction of this neurodegenerative disorder have been proposed as were reviewed for this article, among them oxidative stress and resulting apoptosis can be emphasized. Nevertheless, there is little synchronized evidence on subclinical electrophysiological findings that limit us to reach a strong conclusion on the diagnostic or prognostic use of EMG and NCV for acute and occupational exposures to OPs.