Epidemiology of neuroleptic malignant syndrome

The authors reviewed the trends in the incidence of neuroleptic malignant syndrome (NMS) in studies recently reported in various countries. Possible reasons for the differences in reported incidences were considered. The authors identified publications in English (and their cross-references) that estimated the incidence of NMS with a retrospective or prospective design. They compared the incidence in studies from the United States with those from other countries. The initial retrospective studies from the United States reported higher incidence rates of NMS than did similar studies from elsewhere. More recent prospective studies from the United States report a much lower incidence. Neuroleptic malignant syndrome remains a rare complication of psychotropic treatment if the syndrome is defined stringently. The high incidence reported in earlier studies in the United States can be explained by retrospective study design, loose diagnostic criteria, adherence to an amorphous "spectrum concept," and clinical practices in vogue.