Increased Sensitivity to Rocuronium and Atracurium in Mitochondrial Myopathy

Purpose: To describe the prolonged effect of the intermediate-acting, non-depolarising neuromuscular blocking agents rocuronium and atracurium in a 29-yr-old apparently healthy woman.

Clinical Features: Because of abdominal pain the patient was scheduled for explorative laparoscopic pelvic examination. General anaesthesia was induced with fentanyl, midazolam and propofol. Muscle relaxation was achieved with 0.6 mg.kg-1 rocuronium. Anaesthesia was maintained with nitrous oxide and propofol. Two Hz train-of-four stimulation every 15 sec evoked no twitch responses until 60 min after rocuronium. Further relaxation was achieved with 0.075 mg.kg-1 atracurium after which twitch responses recurred after 45 min. Fifteen minutes later neuromuscular blockade was successfully reversed with atropine and neostigmine. The postanaesthetic course was uneventful. Because of the increased sensitivity to rocuronium and atracurium the patient was re-evaluated postoperatively. History revealed occasional double vision, fatigue, muscle cramps, stiffness and myoglobinuria. Clinical neurological examination showed ptosis, tremor, ataxia and bradydiadochokinesia. A standardised lactate stress testing on a bicycle was pathological and, after muscle biopsy, the diagnosis of mitochondrial myopathy was established.

Conclusion: An increased sensitivity to rocuronium and atracurium may occur in patients with mitochondrial myopathy. In these patients appropriate dosing of muscle relaxants and adequate monitoring of the neuromuscular blockade are required. If an increased sensitivity to rocuronium and atracurium occurs in an apparently healthy subject, further neurological investigations should follow.