[Anesthetic managements of a patient with congenital myotonia (Becker type)]

A 55-year-old woman with congenital myotonia (Becker type), diagnosed by muscle biopsy and gene examination, underwent a right lower lobectomy assisted with thoracoscopy for lung cancer. After epidural tube replacement at T 9-10, general anesthesia was introduced with propofol 2.5 mg x kg(-1) and fentanyl 2.5 mcg x kg(-1). Vecuronium was administered prudently for muscle relaxation assessed with T 1 response (%) and train-of-four (TOF) ratio (%). T 1 response decreased to 50% 3 min and disappeared 4 min after vecuronium administration. Then she was intubated with a double lumen endobronchial tube. T 1 increased 25% within 27 min and 75% in 40 min. Surgery was uneventful and completed in 180 min. At the end of the operation, there was neither fading of twitch responses nor tetanic responses, and TOF ratio returned to 100%. An acetylcholinesterase inhibitor was not given. She was extubated when normal spontaneous breathing, clear consciousness and adequate pharyngeal reflex were present 25 min after discontinuing propofol. There were no perioperative adverse events including hyperthermia and myoglobinuria related to malignant hyperthermia. In conclusion, we managed the anesthesia for a patient with congenital myotonia (Becker type) with thoracic epidural anesthesia and total intravenous anesthesia. Non-depolarizing muscle relaxant could be used safely at the same dose as that used in non-myotonic patients, and did not cause malignant hyperthermia.