Parkinsonism after Carbon Monoxide Poisoning

Of 242 patients with carbon monoxide (CO) poisoning examined between 1986 and 1996, parkinsonism was diagnosed in 23 (9.5%). There were 11 men and 12 women. The age at onset ranged from 16 to 69 (mean 45.8) years, with the peak incidence during the 6th decade. The latency before the appearance of parkinsonism varied from 2 to 26 (median 4) weeks, but parkinsonism developed within 1 month after an acute insult in the majority of the patients. All showed encephalopathy with mildly to severely impaired cognitive functions during or immediately after delayed CO sequelae. The common symptoms were gait disturbance, impaired mentality, urinary incontinence, and mutism. The most frequent signs were short-step gait, hypokinesia, masked face, increased muscle tone (rigidity), glabella sign, grasp reflex, and retropulsion. Intentional tremor was occasionally found, but resting tremor could not be seen. There was no correlation between the neuroimaging findings and the development of parkinsonism. Levodopa and anticholinergic drugs were not effective. Of 16 patients followed up for 1 year, 13 (81.3%) recovered spontaneously within 6 months. In conclusion, parkinsonism after CO poisoning is not rare and usually appears as a part of delayed CO encephalopathy. Any drug is not effective, but the prognosis is good.