Masseteric muscle spasm as a normal response to suxamethonium.

The myotonic response of the masseter muscles following various doses of suxamethonium was measured using a unique myotonometer in 50 apparently healthy patients, the majority of whom showed a myotonic response which lasted less than 100 s. A maximum increase in masseter tone was found to be greater than 1 kg in five patients, and 12 patients developed a maximum tone of greater than 500 g. An increased masseter tone of this degree might be interpreted as "masseteric muscle spasm" by the anaesthetist. The value of masseteric muscle "spasm" as an early sign of malignant hyperthermia is questioned.