Delayed-onset encephalopathy and coma in acute organophosphate poisoning in humans

The objective of the study was to describe the clinical characteristics and course of delayed-onset organophosphate (OP) poisoning. In our clinical experience, we have noticed patients with onset of deep coma 4-7 days after hospital admission, clinical features that have not been previously described. We set up a prospective observational study over 1 year to formally characterize this observation. Thirty-five patients admitted to the intensive care unit (ICU) with severe OP poisoning and treated with atropine and supportive therapy were followed up. Oximes were not administered. Three patients developed delayed-onset coma after presenting with normal or near normal Glasgow coma score (GCS). They developed altered conscious state rapidly progressing to deep coma, 5.0+/-1.0 (mean+/-S.D.) days after OP ingestion. The GCS persisted at 2T for 4.3+/-2.1 days despite the cessation of sedative drugs at the onset of coma. During this period, the patients had miosed non-reacting pupils and no clinically detectable cortical or brainstem activity. Computed tomography of the brain and cerebrospinal fluid analysis were normal. Electroencephalogram showed bihemispheric slow wave disturbances. Two patients required atropine during this period to maintain heart rate and reduce secretions. In all three patients, no metabolic, infective or non-infective cause of altered conscious state was identified. With supportive therapy the GCS improved to 10T in 8.0+/-2.0 days. All patients survived to hospital discharge. Three other patients who developed a reduction in GCS (3T-7T) by 4.7+/-1.2 days but not progressing to coma and recovering (GCS 10T) in 3.3+/-0.6 days may have manifested delayed-onset encephalopathy. Delayed-onset coma appears to have a distinct clinical profile and course with complete resolution of symptoms with supportive therapy. Although persistent cholinesterase inhibition is likely to have contributed to the manifestations, the mechanism of coma and encephalopathy need to be explored in further trials. The good outcomes in these patients suggest that therapy should not be limited in OP-poisoned patients developing profound coma or encephalopathy during hospitalization.