J. Patel, MB, ChB, Registrar, Department of Anaesthesia, M.J. Harrison, FFARCS, Specialist, Department of Anaesthesia, New Zealand. Accepted 29 April 1990
A 4 year old boy with Williams syndrome developed masseter spasm after halothane and suxamethonium. He did not develop malignant hyperthermia; the surgery was accomplished with a nontriggering anaesthetic and no further problem.
Williams syndrome is a very rare disease associated with an elfin face, mental retardation and cardiovascular anomalies. The latter can take the form of supravalvular aortic stenosis and/or pulmonary supravalvular stenosis. All patients have the same characteristic facial appearance, partly determined by the mandibular hypoplasia. There are various dental anomalies including hypoplastic teeth. Idiopathic hypercalcemia in infancy is thought to be associated with the syndrome. The aortic stenotic lesions seen in idiopathic hypercalcemia and in experimental vitamin D intoxication are similar and it has been suggested that there might be a metabolic disorder in utero.
A 4-year-old Caucasian boy who weighed 15 kg with Williams syndrome was presented for correction of left strabismus. His exercise tolerance seemed to be normal and he had had an uneventful general anaesthetic for bilateral herniorraphy. Tracheal intubation was considered potentially difficult because he had protruding top teeth and a relatively hypoplastic mandible. He was premedicated with diazepam 5 mg by mouth since he was known to be of a difficult temperament. Sodium citrate 7.5 ml was given before anesthesia which was easily induced with halothane and nitrous oxide in oxygen. The trachea was intubated with a 4-mm oral Rae tracheal tube but he was subsequently extubated because of an excessive leak around the tracheal tube. He developed intractable laryngospasm during laryngoscopy for re-intubation that required a dose of muscle relaxant. Suxamethonium 10 mg was given but seemed to be ineffective and a further 5 mg was given.
The Masseter spasm was evident after the second dose and consequently the halothane was discontinued. The masseter spasm resolved spontaneously over a period of about a minute, and vecuronium 1 mg was given to facilitate intubation. The 4.5-mm tracheal tube was a tight fit and he was extubated again and re-intubated with the original tube. A throat pack was inserted. Anaesthesia was maintained with nitrous oxide in oxygen and 5 mg fentanyl. He required no further muscle relaxant. No other features of malignant hyperthermia were seen.
The patient showed no signs of awareness during the procedure and was extubated awake at the conclusion of the surgery. There were no postoperative problems. Biochemistry performed a week after operation was within normal limits. The creatine kinase was 122 IU/litres. A muscle biopsy was not performed nor was the urine myoglobin measured.
There is only one report in the anaesthetic literature on Williams syndrome. Laryngoscopy was not difficult in our case although intubation problems should be considered because of the dysmorphic features already mentioned. Contrary to the report of van Beuren el al this patient had a difficult temperament. Hypotonia may be present in Williams syndrome, and this disorder of muscle tone should warn of a possible interaction with anaesthetic agents. There are, however, no data that suggest an increased incidence of masseter spasm or malignant hyperthermia in these patients. The incidence of masseter spasm varies depending on the anaesthetic technique. It is higher in patients induced with halothane and suxamethonium than those induced with thiopentone and suxamethonium. An incidence of about 1 % in children anesthetized with halothane and suxamethonium has been reported. It is well recognized that the incidence of masseter spasm is greater in patients undergoing strabismus surgery. Carroll found a fourfold difference when comparing the incidence in strabismus patients with patients without strabismus.
Christian et al. found a much lower incidence of masseter spasm in children, approximately 1 : 100,000 but they assumed that they were reporting a different condition or reporting a more severe degree of the same condition. There is some debate in the literature whether masseter spasm should still be regarded as an early; sign of malignant hyperthermia.
Van der Spek et al. measured mouth opening after induction of muscle relaxation with suxamethonium, pancuronium and vecuronium in children and found there was a highly significant reduction in mouth opening and increase in jaw stiffness with suxamethonium (p < 0.0001). Patients who received pancuronium or vecuronium did not show this effect. It would appear that an increase in masseter muscle tone with suxamethonium is normal and an exaggerated response may clinically be taken to be masseter spasm.
This child exhibited excessive masseter tone after the use of halothane and suxamethonium: This may have been an exaggerated normal response, but in the presence of other congenital abnormalities of the musculoskeletal system the danger of malignant hyperthermia was considered a real possibility and appropriate action taken.