Malignant hyperthermia testing in probands without adverse anesthetic reaction.

BACKGROUND Malignant hyperthermia (MH) is triggered by reactions to anesthetics. Reports link nonanesthetic-induced MH-like reactions to a variety of disorders. The objective of the authors was to retrospectively investigate the reasons for referrals for MH testing in nonanesthetic cases and assess their phenotype. In addition, the response to the administration of oral dantrolene in nonanesthetic probands with positive caffeine-halothane contracture test (CHCT) was investigated. METHODS Following institutional research ethics board approval, probands without reaction to anesthesia, who underwent CHCT, were selected. Clinical details and response to dantrolene were analyzed. RESULTS In total, 87 of 136 (64%) patients referred for nonanesthetic indications tested positive to the CHCT. Of these, 47 with a high creatine kinase (CK), 9 with exercise-induced rhabdomyolysis and/or exercise intolerance, 2 with high CK and exercise-induced rhabdomyolysis and/or exercise intolerance, 15 with postviral chronic fatigue, and 14 with muscle weakness of unknown etiology had a positive CHCT. These patients had a higher CK compared with those with negative CHCT. Oral dantrolene improved the musculoskeletal symptoms in 28 of 34 (82%) CHCT-positive patients. Response to treatment was associated with a significantly higher pretreatment CK and a greater posttreatment CK reduction. CONCLUSIONS A positive CHCT may represent more than simply an anesthetic-related disorder. Individuals with positive CHCTs may exhibit muscle symptoms without exposure to MH-triggering anesthetics. Oral dantrolene may be useful in alleviating these symptoms.