Abnormal relaxation rates in subjects susceptible to malignant hyperthermia

The acute malignant hyperthermia crisis appears to be mediated by a sudden and sustained rise in the concentration of sarcoplasmic calcium, leading to a prolonged muscle contraction. It is not known whether calcium metabolism in skeletal muscle is abnormal in malignant hyperthermia susceptible (MHS) subjects under normal conditions. A hypermetabolic state in skeletal muscle can be assessed in vivo by measuring relaxation rate. In the present study the relaxation rate was measured in the adductor pollicis muscle after electrical stimulation of the ulnar nerve. Ten MHS subjects with no clinical symptoms of muscle disease were investigated. Relaxation rates were found to be significantly higher in the MH-susceptible subjects compared with controls even under normal conditions (p less than 0.001). Determination of relaxation rate could thus be considered a possible addition to those methods currently available for the diagnosis of MHS.