Investigation of malignant hyperthermia in Sweden.

One hundred and thirty patients from 52 families were investigated for susceptibility to malignant hyperthermia (MH). The diagnosis of MH susceptibility (MHS) was made by in vitro exposure of muscle to halothane and to caffeine, according to the protocol established by the European malignant hyperpyrexia group. In addition, 13 normal control biopsies were obtained from the same muscle and with the same anaesthesia as in the MH patients. These control results agree with and confirm the criteria formulated in the European MH group. The results are compared with our first 85 investigations performed prior to the establishment of the protocol. The main difference compared to the earlier material is the addition of an equivocal group (MHE), whose muscle reacted in vitro to either halothane or caffeine, but not both. All the families referred because of a fulminant MH reaction contained MHS or MHE members. There was a greater incidence of MH-negative families, suggesting an increased suspicion of MH amongst the clinicians.