Electrodiagnostic tests in the detection of malignant hyperthermia

Malignant hyperthermia (MH) can be a catastrophic and sometimes fatal reaction in certain susceptible individuals who are exposed to skeletal muscle relaxants such as succinylcholine and/or certain inhalation anesthetics such as halothane. In an attempt to develop a safe, simple in vivo test to identify the at-risk patients, repetitive nerve stimulation (RNS) and electromyographic (EMG) studies were performed on 9 patients with MH, 15 patients suspected of having MH, and 9 control subjects. Serial recordings were made following injections of caffeine sodium benzoate, succinylcholine, and halothane at the test site. Measurements were done on the amplitude of the evoked compound motor action potentials (CMAP), on RNS, and on the number of negative peaks of motor unit potentials (MUP) on maximum EMG recruitment. The results showed the effects of the drugs on amplitudes of the CMAPs to be significant (P less than 0.001) in all three groups, but no significant differences were found among the groups (P = 0.93). The negative peaks of MUP on EMG recording showed a significant difference upon introducing succinylcholine (P less than 0.001), and significant interaction effects of the treatment by the patient group. Preliminary comparisons of in vivo tests with in vitro contracture tests in nine patients showed good correlation.