Beyond the cholinergic crisis

Organophosphates (OP) are the most frequently involved pesticides in acute poisoning. In Sri Lanka it has been ranked as the sixth or seventh leading cause of hospital deaths for many years. Neurotoxic effects of acute OP have been hitherto under-explored. The aims of the studies were to assess the effects of acute OP poisoning on somatic, autonomic nerves, neuromuscular junction (NMJ), brain stem and cognitive function. Methods: Patients following self-ingestion of OP were recruited to cohort studies to evaluated the function of somatic, autonomic nerves, NMJ, brain stem and cognition. Motor and sensory nerve function was tested with nerve conduction studies. Cardiovascular reflexes based autonomic function tests and sympathetic skin response (SSR) was used to evaluate autonomic function. NMJ function was assessed with slow repetitive supramaximal stimulation of the median nerve of the dominant upper limb. Brain stem function and cognitive function were assessed with Brain Stem Evoked Response Audiometry (BERA) and Mini Mental State Examination (MMSE) respectively. The data of the patients were compared with age, gender and occupation matched controls. Results: There were 60-70 patients and equal number of controls in each study. Motor nerve conduction velocity, amplitude and area of compound muscle action potential on distal stimulation, sensory nerve conduction velocity and F-wave occurrence were significantly reduced. At one week the significant impairment in autonomic function were change of diastolic blood pressure 3 min after standing, heart rate variation during deep breathing (HR-DB), SSR-amplitude and post-void urine volume. All except HR-DB were reversed at six weeks. No significant impairment of NMJ function, BERA and MMSE were noted. Conclusions: Sub clinical somatic and autonomic nerve dysfunction was observed. There were no strong evidence of long term effects on NMJ, brain stem and higher function.