Malignant hyperthermia susceptibility in neuroleptic malignant syndrome

The relationship between neuroleptic malignant syndrome (NMS) and malignant hyperthermia (MH) was investigated using the in vitro skeletal muscle contracture test to screen for MH-susceptibility in NMS patients. The maximum contracture tension which developed following exposure to halothane (1-3%), and incremental doses of fluphenazine (0.2-25.6 mM) was measured in muscle obtained from seven NMS, six MH, and six control patients. Comparison of the cumulative responses to fluphenazine revealed no significant differences among the groups. However, the response (mean +/- SEM) to halothane in the NMS group (1.7 +/- 0.7 g), which was similar to the response in the MH group (1.5 +/- 0.2 g), was significantly greater than the response found in controls (0.2 +/- 0.1 g). In addition, five of seven NMS patients could be diagnosed as MH-susceptible, based on the development of muscle contractures greater than 0.7 g in response to 1-3% halothane. In contrast, none of the controls were MH-susceptible. These findings appear to correlate with clinical evidence suggesting an association between NMS and MH.