Slow Repetitive Nerve Stimulation in Patients with Acute Organophosphorus Poisoning after Clinical Recovery

Background: Prolonged inhibition of acetylcholine esterase may lead to the intermediate syndrome. Neuromuscular junction (NMJ) dysfunction has been shown with repetitive nerve stimulation (RNS). Subclinical NMJ dysfunction may also occur. We aimed to examine the NMJ function following acute organophosphorus (OP) poisoning by using exercise modified slow RNS. Methods: A cohort study was conducted with matched controls. Patients with acute OP poisoning were enrolled. NMJ function, muscle power and tendon reflexes were assessed at discharge and six weeks after exposure. NMJ function was assessed with exercise modified supramaximal slow RNS of the median nerve. Results: There were 68 patients and 71 controls. Mean (SD) age of patients and controls were 32 (12) and 33 (12) years. In some particular amplitude, the decrement response was statistically significant. They were decrement response at rest, at fourth amplitude (95% CI: -0.2 to -2.7) and two minutes post-exercise at fourth and fifth amplitudes (95% CI: -0.8 to -5, -1 to -5 respectively) in the second assessment compared to controls, decrement response at rest at fourth and fifth amplitudes (95% CI: -4 to -0.5, -3.9 to -0.01 respectively) and two minutes post-exercise at fourth amplitude (95% CI: -5 to -0.8) in the second assessment compared to the first assessment. Patients in the first assessment and controls showed more than 8% decrement response either to the second, fourth or fifth stimuli in seven and five occasions respectively. Conclusion:  There was no significant neuromuscular junction dysfunction assessed by exercise modified slow repetitive stimulation following acute exposure to OP. Since, NMJ dysfunctions are likely to occur following OP poisoning, other electrodiagnostic modalities such as SF-EMG are probably more efficient to assess these abnormalities.