Sleep-induced masticatory myoclonus: a rare parasomnia associated with insomnia.

Tonic and rhythmic activity of the masticatory muscles accompanied by a loud and grating or clicking sound characterizes bruxism, a well-recognized parasomnia. We describe a 63-year-old man who complained of insomnia due to repeated tongue nibbling during sleep. Nocturnal polysomnographic recordings showed brief (50-100-ms) myoclonic jerks of myloioideus and masseter muscles occurring during phase 1 of sleep and leading to troublesome tongue nibbling with arousal of the patient. Hypnograms showed reduction of phase 2 and absent phases 3-4 and REM. Different pharmacological treatments including clomipramine, benzodiazepines, and carbamazepine were ineffective. A purposive interdental plate was placed to prevent jaw closings during sleep: masticatory myoclonus still persisted, but it did not provoke arousals; insomnia disappeared and night hypnograms improved.