This combination produces a similar reaction in some patients with muscular dystrophy and myotonia. Malignant hyperthermia affects about 1 in 20,000 patients. Susceptibility to the disorder is inherited in an autosomal dominant pattern. As a result, Ca-induced biochemical reactions are accelerated, causing severe muscle contractions and an elevated metabolic rate. Malignant hyperthermia may develop during anesthesia or in the early postoperative period.
Clinical presentation varies, depending on the drug used and the patient's susceptibility.
Muscular rigidity is often the first sign, followed by tachycardia, other arrhythmias, acidosis, shock, and hyperthermia. Early diagnosis and prompt treatment are required to reduce morbidity and mortality. The in vitro caffeine-halothane contracture test is a specific diagnostic test for malignant hyperthermia but is available at few centers in North America. Muscle biopsy and elevated creatine kinase levels may be used to identify sensitive members of the patient's family. Surgery and anesthesia should be discontinued as rapidly as possible.