Reduced duration of muscle relaxation with rocuronium in a normocalcemic hyperparathyroid patient

To report a case of reduced duration of action of rocuronium in a patient with normocalcemic hyperparathyroidism (HPT). A 56-yr-old patient with primary HPT, who had had surgical resection of three and a half parathyroid glands nine months previously, was referred to our institution for further investigation of a persistent increase in parathyroid hormone. Preoperatively, the patient had a normal serum ionized and total calcium. The patient was diagnosed with a persistent parathyroid adenoma and was scheduled for an elective parathyroidectomy. General anesthesia was induced with iv propofol, fentanyl and succinylcholine. Intraoperatively, anesthesia was maintained with nitrous oxide in oxygen, and isoflurane. Neuromuscular blockade was attained using incremental doses of rocuronium. The average duration of 0.15 mg x kg(-1) incremental doses of rocuronium was 5.9 min (expected: 13-18 min), and that of 0.2 mg x kg(-1) was ten minutes (expected: 19-23 min). Primary HPT even in the absence of hypercalcemia may result in resistance to competitive blockade by rocuronium. It suggests that primary HPT may cause acetylcholine receptor up-regulation resulting in hyposensitivity to non-depolarizing muscle relaxants.