Spectrum of susceptibility to malignant hyperthermia--diagnostic dilemma.

Utilizing established in vitro muscle contracture tests, we have identified three diagnostic contracture phenotypes for malignant hyperthermia susceptibility (MHS) among 103 patients. Phenotype H is an unequivocal diagnostic result for MHS, as is the nonsusceptible phenotype N. The third diagnostic group, phenotype K, represents an equivocal diagnostic response. To provide a basis for understanding relationships between contracture phenotypes and MHS, pigs with phenotypes H, K, and N were exposed to a standardized anesthetic protocol for assessing MHS. During the anesthetic challenge, phenotype H pigs developed a more severe form of the MH syndrome than did phenotype K pigs. Comparing phenotype H v K average responses, VO2 increased four- v twofold; lactate increased 13- v 9-fold; and temperature increased 41.7 degrees C v 39.2 degrees C, respectively. These values either had no change or decreased in the phenotype N pigs. Results of this study suggest that a spectrum of MHS exists among the human population.