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Clinical characteristics of malignant hyperthermia (MH) in pediatric patients have not been elucidated. In this study, we used the North American Malignant Hyperthermia Registry to determine differences in clinical characteristics of acute MH across pediatric age groups. We hypothesized that there are differences in clinical presentation, clinical course, and outcomes, which correlate with age. A secondary aim was to determine the types of preexisting medical conditions associated with pediatric MH.We performed a retrospective review of the North American Malignant Hyperthermia Registry to identify pediatric subjects (up to and including 18 years) with an MH clinical grading score at or above 35 indicating “very likely” or “almost certain” MH. Preoperative patient characteristics, perianesthetic factors, and outcome data were compared for 3 cohorts based on age: 0 to 24 months, 25 months to 12 years, and 13 to 18 years. We used statistical analysis to determine differences among the groups.We analyzed 264 records: 35 in the youngest age group, 163 in the middle age group, and 66 in the oldest group. There was no indication of any predisposing risk factors for MH based on family history or physical examination. Sinus tachycardia, hypercarbia, and rapid temperature increase were the most common signs of acute MH (observed in 73.1%, 68.6%, and 48.5%, respectively) and were more common in the oldest age cohort. Higher maximum temperatures and higher peak potassium values were seen in the oldest age cohort. Masseter spasm was more common in the middle age cohort. The youngest age cohort was more likely to develop skin mottling and was approximately half as likely to develop muscle rigidity. The youngest age group also demonstrated significantly higher peak lactic acid levels and lower peak creatine kinase values. Treatments were similar across age cohorts. There were 10 MH-associated deaths, 6 in the middle age group and 4 in the oldest age group. Recrudescence of symptoms after initial treatment occurred in 14.4% of subjects, with no difference across age cohorts. Two of these subjects, 1 in the middle age group and 1 in the oldest age group, died after the recrudescence event.There are differences in clinical characteristics of acute MH among different age cohorts in childhood. Older subjects demonstrated higher body temperatures and higher potassium levels, and the youngest subjects had greater levels of metabolic acidosis. Most children in each age group were phenotypically normal before developing MH.