Malignant hyperthermia susceptibility in a patient with concomitant motor neuron disease.

Laboratory confirmation of a clinical suspicion of malignant hyperthermia (MH) susceptibility by the standard in vitro contracture test remains inconclusive in patients reacting only to caffeine or halothane (called 'Equivocal') or in patients with concomitant neuromuscular disease. The detection of point mutations in the ryanodine receptor gene potentially provides additional information in these cases. The diagnostic value of the Gly341 Arg mutation in a patient reacting in vitro only to caffeine was reported previously by Quane et al. (1994). The present report describes a patient with motor neuron disease carrying the Gly341 Arg mutation, expanding the diagnostic value of this mutation to the group of patients with neuromuscular diseases.