Acute thyroid crisis on induction of anaesthesia.

Thyroid crisis on induction of anaesthesia was treated with dantrolene, because of a mistaken diagnosis of malignant hyperthermia. There was immediate improvement after dantrolene with reduction in muscle rigidity, mental confusion and pyrexia. High circulating T4 has an effect on calcium flux across the sarcoplasmic reticulum and dantrolene may inhibit this pathological mechanism. We suggest the same dosage regimen as is used in the treatment of malignant hyperthermia.