Postoperative malignant hyperthermia in a one-year-old girl with down syndrome: a case report.

Malignant hyperthermia (MH) is a severe complication of general anesthesia, characterized by myotonia, muscle rigidity, acidosis, hyperthermia, tachycardia, and hyperpnea. Herein, we report the case of a 1-year-old girl with congenital heart disease (CHD) and Down syndrome (DS) who underwent cheiloplasty. Approximately 50 min after the completion of general anesthesia, she presented with tachycardia, hyperpnea, and fever, notably without any muscle-related symptoms. Initially, a respiratory infection was suspected, prompting antibiotic administration. However, by postoperative day 2, her symptoms persisted and were accompanied by elevated creatine kinase (CK) and transaminase levels. These findings led us to consider acute heart failure (AHF) secondary to CHD as a potential cause of her symptoms, but her condition did not improve despite cardiac intervention. By postoperative day 6, a markedly elevated plasma myoglobin level suggested the occurrence of MH, even without muscle symptoms. Administration of dantrolene led to the rapid resolution of her symptoms. Genetic testing subsequently confirmed that she had developed postoperative MH. This case highlights the difficulty in diagnosing MH in children with DS associated with CHD.