Patient Safety Section Editor: Sorin J. Brull Prevalence of Malignant Hyperthermia Due to Anesthesia in New York State, 2001–2005 Joanne E. Brady, SM* Lena S. Sun, MD*† Henry Rosenberg, MD‡§ Guohua Li, MD, DrPH* BACKGROUND: Malignant hyperthermia (MH) is a pharmacogenetic syndrome that variably expresses itself on exposure to triggering agents. MH prevalence in the United States is not well documented. In this study, we assessed the prevalence of MH in New York State hospitals. METHODS: Using New York hospital discharge data for the years 2001 through 2005, we identified all patients with a diagnosis of MH due to anesthesia using International Classification of Diseases, Ninth Revision, Clinical Modification code 995.86. MH prevalence was evaluated by demographic and clinical characteristics. RESULTS: Of the 12,749,125 discharges from New York hospitals during the study period, 73 patients had a recorded diagnosis of MH due to anesthesia. Nearly three quarters of the MH patients were male and 71% were patients from emergency/urgent admissions. The estimated prevalence rate of MH was 0.96 (95% confidence interval [CI] 0.67–1.24) per 100,000 surgical discharges and 1.08 (95% CI 0.75–1.41) per 100,000 discharges in which there was any indication of exposure to anesthesia. The estimated prevalence of MH for males was 2.5 to 4.5 times the rate for females. CONCLUSION: The prevalence of MH due to anesthesia in surgical patients treated in New York State hospitals is approximately 1 per 100,000. MH risk in males is significantly higher than in females. (Anesth Analg 2009;109:1162–6) Malignant hyperthermia (MH), also called malig- nant hyperpyrexia, is an autosomal dominant genetic disorder of the skeletal muscle. This condition is a pharmacogenetic syndrome that variably expresses itself on exposure to triggering agents, which include inhaled volatile anesthetics (e.g., halothane, isoflu- rane, enflurane, and sevoflurane) and depolarizing muscle relaxants (e.g., succinylcholine). 1–3 MH is characterized by signs of hypermetabolism caused by the release of calcium from the sarcoplasmic reticulum, 2–4 increased oxygen consumption, and increasing and unexplained increase in end-tidal CO 2 that does not decrease with increasing minute ventila- tion, tachycardia, muscle rigidity, hyperthermia, and re- spiratory and metabolic acidosis. 2– 4 Other signs of MH may include disseminated intravascular coagulation, car- diac arrhythmias, hyperkalemia, hyperphosphatemia, hypocalcemia, rhabdomyolysis, myoglobinuria, and mottled skin. 2– 4 A clinical grading scale for MH was developed in 1994 to create a standard clinical case definition and, in part, to allow comparisons between groups of patients that were defined by similar characteristics. 5 The laboratory diagnosis of MH susceptibility is based on the contracture response of biopsied vastus muscle to graded concentra- tions of halothane or caffeine. 3,6 –9 More recently, a DNA- based test has been introduced, but the diagnostic utility of the test has not been adequately assessed. Estimates of MH incidence and prevalence have varied greatly. For example, separate epidemiologic studies with selected patient groups have found incidence rates of MH ranging from 1 in 200 to 1 in 50,000 anesthetics for patients aged 18 years and older. 10 –12 A study in Denmark found a prevalence of MH susceptibility of 1 in 250,000. 13 In France, a study cites 1 in 10,000 as the estimated prevalence for MH susceptibility due to anesthesia, but given 6 loci and 2 genes associated with MH and the incom- plete penetrance of the MH trait, the authors contend that a prevalence between 1 in 2000 to 1 in 3000 may be a better approximation of MH susceptibility. 14 In From the *Department of Anesthesiology; †Department of Pedi- atrics, College of Physicians and Surgeons Columbia University, New York, New York; ‡Department of Medical Education and Clinical Research, Saint Barnabas Medical Center, Livingston, New Jersey; §Malignant Hyperthermia Association of the United States, Sherburne, New York; and Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York. Accepted for publication March 9, 2009. Supported, in part, by the Malignant Hyperthermia Association of the United States, Sherburne, NY. This work was attributed to Department of Anesthesiology, College of Physicians and Surgeons, Columbia University. Address correspondence and reprint requests to Guohua Li, MD, DrPH, Department of Anesthesiology, Columbia University, 622 West 168th Street, PH5-505, New York, NY 10032. Address e-mail to gl2240@columbia.edu. Copyright © 2009 International Anesthesia Research Society DOI: 10.1213/ane.0b013e3181ac1548 Vol. 109, No. 4, October 2009 1162