The Spectrum and clinical correlates of electrodiagnostic abnormalities in acute organophosphorus poisoning : a study of 55 patients.

Electrodiagnostic findings in 55 patients with acute organophosphorus intoxication have been correlated with clinical severity. Patients were assigned 3 grades of intoxication, depending upon the clinical severity of poisoning, muscarinic and nicotinic manifestations, ventilatory failure and altered sensorium. Repetitive responses upon single supramaximal stimulation of the median motor nerve were noted in all three grades of intoxication. In mild intoxication (grade I), low frequency repetitive nerve stimulation (< 3 Hz) produced no change in the amplitudes of the successive compound muscle action potentials. High frequency repetitive nerve stimulation (30 Hz and 50 Hz) resulted in either incremental responses (18 out of 29 cases), decremental responses (5 out of 29 cases) or decremental - incremental responses (6 out of 29 cases). Thirty five electrodiagnostic evaluations were performed in patients with overt neuromuscular weakness but not requiring mechanical ventilation (grade 2). Decremental responses were noted in only 3 instances at low frequency (< 3 Hz) repetitive nerve stimulation and in 34 out of 35 cases with high rates of stimulation. Patients who required mechanical ventilation had decremental responses at high (30 and 50 Hz) (12 out of 12 cases) as well as low rates (3 and 5 Hz) (7 out of 12 cases) of repetitive nerve stimulation. Serial electrodiagnostic evaluations, which were done in 12 patients, revealed that neuromuscular transmission abnormalities were either mild or absent within 24 hours in 9 patients. A deterioration in the neuromuscular transmission studies was noted during subsequent examinations performed, 1- 4 days later in these 9 patients. Electrodiagnostic testing is highly sensitive for establishing a diagnosisof organophosphorus poisoning and correlates well with clinical findings and the severity of poisoning. It may, however be normal in the early stages of intoxication.