[Diagnosis of malignant hyperthermia susceptibility. 2. Anesthesia for muscle biopsy. Differential diagnosis in negative test results].

At present the in vitro caffeine-halothane contracture test is the only test to predict susceptibility to malignant hyperthermia (MH) with acceptable sensitivity and specificity. Anaesthesia is necessary for the excision of muscle bundles from the vastus lateralis muscle. MATERIAL AND METHODS. Between 1983 and 1991, muscle biopsies were taken from 350 patients, 233 children and 117 adults. In 197 cases, trigger-free general anaesthetics were supplemented by ventilation, via mask in 124 cases and via tracheal intubation in 73 cases. One hundred and fifty-three muscle biopsies were performed under regional or local anaesthesia with or without sedation. Fourteen of the patients with regional anaesthesia needed an additional general anaesthetic to tolerate the operation. For premedication midazolam was administered orally. The general anaesthetics consisted of etomidate or propofol with fentanyl or alfentanil, always with nitrous oxide and oxygen. For local anaesthesia we used procaine or prilocaine. During the first 3 years local infiltration of the thigh was used, but subsequently direct nerve blockade of the femoral nerve and the lateral cutaneous femoral nerve was preferred. RESULTS. In all cases of general anaesthesia and in 91.6% of cases of regional anaesthesia operating conditions were very good. Fourteen (8.4%) of the patients with regional anaesthesia needed an additional general anaesthetic. There were no severe complications noticed. Moderate complications were found in 29 of the 194 paediatric general anaesthesias (15%) and in 5 of the 117 regional anaesthesias in adults (4%); all were easy to treat. The 50 paediatric regional anaesthesias and the three general anaesthesias in adults were without complications. DISCUSSION. For muscle biopsies, trigger-free general anaesthesia can be recommended as well as peripheral nerve blockades. Complete monitoring is necessary, even for this minor procedure: ECG, blood pressure, pulse oximetry, capnometry, measurement of body temperature and blood gas status. Differential diagnosis in negative test results. In patients who suffer an anaesthetic incident, the following disease must be considered: myopathies (especially the congenital myopathies and muscular dystrophies), respiratory problems due to pulmonary infection and obstruction, metabolic disorders of various origins, and the problem of masseter spasm.