Nerve conduction study as a diagnostic tool in atypical presentation of accidental organophosphorus poisoning

Poisoning with organophosphorus (OP) compounds is a worldwide phenomenon. However, atypical presentation of OP toxicity, particularly when there is a paucity of muscarinic manifestations, can be a diagnostic challenge. We report a patient with atypical symptoms where exposure to OP poison was not clearly determined. Motor nerve conduction studies done to rule out acute motor neuropathy revealed that a single supramaximal stimulus-evoked repetitive compound motor action potentials. As this finding is the earliest and most sensitive indicator of acetylcholine esterase inhibition, OP poisoning was suspected. Decreased plasma acetylcholinesterase levels confirmed the diagnosis. The patient recovered completely with treatment. Although the diagnostic hallmark of OP poisoning is a reduction in serum and red blood cell cholinesterase activity, clinicians should be alert to recognize evidence of neuromuscular transmission failure seen on nerve conduction study to diagnose atypical or concealed cases of OP poisoning.