Harrison_2025_Biomol.Biomed__

Masseter muscle spasm after succinylcholine can herald malignant hyperthermia (MH) in genetically susceptible individuals. We aimed to describe the perioperative course and genetic findings in a patient who developed transient masseter spasm and postoperative rhabdomyolysis after general anesthesia. This single-patient case report draws on perioperative observations, laboratory testing, and whole-genome sequencing. Immediately after induction with propofol and succinylcholine, the patient experienced transient masseter spasm; anesthesia was then maintained with total intravenous anesthesia (propofol and remifentanil). Postoperatively, laboratory studies showed severe rhabdomyolysis with mild pigment nephropathy; the patient received intravenous hydration, laboratory values normalized by postoperative day 4, and discharge occurred in good condition. Whole-genome sequencing identified heterozygous ryanodine receptor 1 (RYR1) c.1840C>T (p.Arg614Cys)-a known MH-susceptibility variant in the skeletal-muscle ryanodine receptor-and butyrylcholinesterase (BCHE) c.293A>G (p.Asp98Gly), which reduces butyrylcholinesterase activity and delays succinylcholine hydrolysis. The coexistence of these variants likely synergistically increased sarcoplasmic reticulum Ca^2 release and prolonged succinylcholine effect, precipitating rhabdomyolysis; to our knowledge, this appears to be the first reported case linking concurrent RYR1 and BCHE variants to rhabdomyolysis following general anesthesia.