What is the significance of masseter muscle rigidity (MMR)?

What is the significance of masseter muscle rigidity (MMR)?

MMR (trismus) has been reported to occur in 1% of children receiving halothane and succinylcholine for induction. It was previously thought to herald the onset of MH in 50% of cases as confirmed by skeletal muscle biopsy. Recent studies indicate that MMR may occur in otherwise normal patients. In the presence of MMR, whether to continue anesthesia for elective procedures and whether to discon-tinue triggering agents remains controversial. Some suggest that the anesthetic may be safely continued, while others suggest that all such episodes should be treated as MH until proven otherwise by skeletal muscle biopsy.

Other causes of MMR include temporomandibular joint dysfunction, myotonia, and rapid succinylcholine hydrolysis.