Spectrum of Susceptibility to Malignant Hyperthermia???Diagnostic Dilemma

Abstract
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.

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