Evidence for susceptibility to malignant hyperthermia in patients with exercise-induced rhabdomyolysis

Background: Malignant hyperthermia (MH), heat stroke, and exercise-induced rhabdomyolysis (ER) were suspected to be related syndromes. However, it is not known whether individuals with history of ER have an increased incidenc e of susceptibility to MH. To establish an association between ER and susce ptibility to MH, the authors determined the MH status in patients with a hi story of MH-Like episodes induced by physical stress. Methods: Twelve unrelated patients with ER, 18 patients with anesthesia-ind uced MH, and 28 controls were investigated with the in vitro contracture te st (IVCT) according to the European MH Group protocol and the ryanodine con tracture test. In addition, all patients were screened for genetic mutation s, and histology was performed on muscle specimens. Results: Ten ER patients had positive IVCT results, one patient had a negat ive test result, and one patient showed equivocal responses. Samples from p atients with positive IVCT results showed pronounced contractures after exp osition to ryanodine, as opposed to specimens from patients with negative I VCT results, which developed contractures slowly. Three ER patients had mut ations at the ryanodine receptor gene. All anesthesia-induced MH patients h ad positive IVCT results, two of them presented the C1840T mutation. The co ntrol patients had normal contracture test results and no typical MH mutati ons. Histologic examination determined no specific myopathies in any patien t. Conclusions: Regarding these results, the authors recommend performing musc le biopsies for histologic examination and IVCT in patients with ER. In add ition, the patient should be seen by a neurologist and screened for genetic abnormalities to shed light on the genetics of MH.