Malignant hyperthermia upon re-exposure to sevoflurane after an uneventful identical anesthetic in a patient with negative RYR1 and CACNA1S genetic testing: a case report

Background Malignant hyperthermia (MH) is a rare but potentially fatal hypermetabolic crisis triggered by volatile anesthetics. Mortality rises sharply when dantrolene is delayed. MH upon re-exposure to volatile anesthetics is documented. Yet it is uncommon to encounter MH after a prior uneventful identical anesthetic, with onset beyond 2 hours, negative RYR1 and CACNA1S testing, and no on-site dantrolene. Case presentation: A male patient underwent laparoscopic resection of a recurrent adrenal lesion. He had received the same sevoflurane-based anesthetic at the same hospital four months earlier without incident. In this laparoscopic resection of a recurrent adrenal lesion, hypermetabolic signs initiated at approximately 2.0 hours after induction. The clinical diagnosis of MH was made at 2.5 hours after induction. The peak crisis of MH reached at 3.25 hours after induction, manifested by abrupt hypercapnia (EtCO₂ 95 mmHg), hyperthermia to 40.5°C, hyperkalemia (6.5 mmol/L) and metabolic acidosis. Blood pressure fell to 75/40 mmHg and heart rate rose to 165 beats per minute. Masseter spasm was absent. The Clinical Grading Scale score was 63 (“almost certain”). Sevoflurane was stopped immediately. The breathing circuit and soda lime were replaced. Management included hyperventilation, active cooling, correction of acidosis and electrolytes, and norepinephrine infusion. Our institution did not maintain an on-site dantrolene supply. Definitive therapy was delayed for 2 hours while the drug was retrieved from an outside facility. Postoperative targeted sequencing of RYR1 and CACNA1S revealed no pathogenic variants. The patient ultimately recovered without residual complications after ICU admission. Conclusion This case demonstrates that MH can occur despite a prior uneventful anesthetic, despite negative RYR1/CACNA1S screening, and a 2-hour delay onset of MH. It underscores the necessity of maintaining institutional dantrolene stocks and sustained intraoperative vigilance regardless of anesthetic duration or prior unremarkable exposures.