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Masseteric muscle spasm as a normal response to suxamethonium
British Journal of Anaesthesia
|April 1, 1990
Summary
Suxamethonium causes masseter muscle myotonia in healthy patients, with some experiencing significant tone increases. This response may be misinterpreted as masseteric muscle spasm, questioning its utility as an early sign of malignant hyperthermia.
Area of Science:
- Anesthesiology
- Pharmacology
- Muscle Physiology
Background:
- Suxamethonium is a muscle relaxant used in anesthesia.
- Masseter muscle myotonia can occur post-suxamethonium administration.
- Malignant hyperthermia is a rare but serious anesthetic complication.
Purpose of the Study:
- To quantify the myotonic response of masseter muscles to suxamethonium in healthy individuals.
- To assess the clinical significance of increased masseter tone following suxamethonium.
- To evaluate the reliability of masseteric muscle spasm as an early indicator of malignant hyperthermia.
Main Methods:
- A unique myotonometer was employed to measure masseter muscle tone.
- Fifty apparently healthy patients received varying doses of suxamethonium.
- Myotonic responses and maximum increases in muscle tone were recorded.
Main Results:
- The majority of patients exhibited a myotonic response lasting under 100 seconds.
- Five patients showed a maximum increase in masseter tone exceeding 1 kg.
- Twelve patients developed a maximum tone greater than 500 g.
Conclusions:
- Suxamethonium reliably induces masseter muscle myotonia in healthy subjects.
- Significant increases in masseter tone can occur, potentially misdiagnosed as spasm.
- Masseteric muscle spasm is a questionable early sign for diagnosing malignant hyperthermia.