• Sachiko Otsuki, Hirotsugu Miyoshi, Keiko Mukaida, Toshimichi Yasuda, Ryuji Nakamura, and Yasuo M Tsutsumi.
• From the *Department of Anesthesiology and Critical Care, Hiroshima University, Hiroshima, Japan.
• Anesth. Analg. 2022 Jul 1; 135 (1): 128135128-135.

BackgroundMalignant hyperthermia (MH) is an inherited muscle disorder induced by volatile anesthetics and depolarizing muscle relaxants. While the incidence of MH is high in young, there are few reports on the clinical features of pediatric MH. In this study, we selected pediatric cases from an MH database and analyzed the clinical findings by age group. We hypothesized that there would be age-related differences in the clinical characteristics.MethodsA retrospective analysis of MH data collected in our database during 1960 to 2020 was performed to identify pediatric subjects (≤18 years) with a Clinical Grading Scale of ≥35, indicating "very likely" or "almost certain" MH. We compared clinical characteristics among the 0 to 24 month, 2 to 12 year, and 13 to 18 year (youngest, middle, and oldest, respectively) age groups.ResultsData were available for 187 patients: 15 in the youngest age group, 123 in the middle-aged group, and 49 in the oldest age group. Of these, 55 patients (29.4%) had undergone muscle biopsy and muscle contracture test. The mortality rates during the study period were 13.3%, 13.8%, 20.4%, and 15.5% in the youngest, middle, and oldest cohorts and overall, respectively. In contrast, the overall mortality rate from 2000 to 2020 was 8.8%. The most frequent initial symptoms of MH were elevated temperature (46.7%) and generalized muscular rigidity (26.7%) in the youngest cohort, masseter spasm (35.0%) and generalized muscular rigidity (19.5%) in the middle cohort, and elevated end-tidal carbon dioxide (26.5%) and tachycardia (22.4%) in the oldest cohort. Physical examination revealed that elevated temperature, sinus tachycardia, and respiratory acidosis occurred frequently in all groups. The middle cohort had high frequencies of masseter spasm (58.4%; P = .02) and dark urine (75.5%; P = .01) compared to those in the oldest groups, and had a higher peak creatine kinase level compared to those in the 3 groups. Skeletal muscle symptoms tended to be more common in patients administered succinylcholine (generalized muscular rigidity, P = .053; masseter spasm, P < .0001; dark urine, P < .0001). In particular, masseter spasm and dark urine were more common in the middle cohort when succinylcholine was administered (masseter spasm: versus youngest cohort, P = .06, versus oldest cohort, P = .027; dark urine: versus youngest cohort, P = .0072, versus oldest cohort, P = .0015).ConclusionsThe clinical characteristics of pediatric patients with MH vary according to age group. The difference in initial symptoms of MH depending on age group is noteworthy information for the early diagnosis of MH.Copyright © 2021 International Anesthesia Research Society.

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