Sleep‐related tongue biting may not be a sign of epilepsy: A case of sleep‐related faciomandibular myoclonus

Abstract

To the Editors: Tongue biting (TB), frequently reported during generalized tonic–clonic seizures, is considered a sign of elevated diagnostic value in the differential diagnosis of seizures, with a suggested 100% specificity when biting is located on the lateral margin of the tongue (Benbadis et al., 1995). TB is also reported in focal epilepsy, and it has been suggested that it is a possible lateralizing sign of seizure onset (Benbadis, 1996). A 45-year-old woman presented with a 5-year history of sleep-related TB episodes and bleeding involving either the lateral margin of the tongue, its tip, or (more infrequently) the inner cheek. Electroencephalograms (EEGs) were repeatedly normal, whereas a brain magnetic resonance imaging study revealed a right temporopolar meningioma. Epilepsy was diagnosed and carbamazepine was started, but it failed to control the TB episodes. Despite the surgical removal of the tumoral lesion, the patient still reported from 5 to 10 TB episodes/month when first admitted to our Epilepsy Monitoring Unit. At that time, we carried out nocturnal video-polysomnography, including 21 EEG channels and surface electromyography (EMG) from the submental, temporal, masseter, orbicularis oculi, orbicularis oris, and tibialis anterior muscles. The polysomnography revealed a normal sleep structure without EEG abnormalities. In all non-REM sleep (NREM) stages, shock-like jerks (duration 150 ms) were observed, involving the masseter, orbicularis oris, and orbicularis oculi muscles; each jerk produced jaw clenching of variable intensity associated with a sharp sound, coinciding with a brief EEG arousal (Fig. 1). The EMG bursts were not correlated to any EEG potential, as determined by visual inspection of the tracing and by back averaging analysis. The jerks were thus interpreted as the result of a sleep-related-faciomandibular myoclonus (SFRM) and TB the consequence of such a paroxysmal motor phenomenon. Bruxism was not observed in association with SFRM, as was reported in other cases (Vetrugno et al., 2002). In the upper panel, a 30-s NREM stage 2 epoch showing a brief EMG burst involving bilaterally the masseter, the temporal, and the orbicularis oris muscles; the myoclonic jerk is followed by an EEG arousal. In the lower panel, the same episode is displayed in a 3-s epoch; note the absence of any EEG potential preceding the EMG activity. To confirm the hypothesis of a subcortical origin of the jerks, we performed a blink reflex study (measuring the recovery cycle of the R2 component) that revealed a mildly facilitated blink reflex and a significantly faster than normal recovery of the R2 component (Fig. 2). Treatment with clonazepam stopped the TB episodes. The patient (squared line) and controls (n = 10, circled line) R2 recovery values at intervals of 100, 200, 400, 600, and 800 ms. The R2 test response in our patient was 22% of the corresponding response at 100 ms; subsequently the R2 response recovered gradually to reach 74% at 200 ms, 78% at 400 ms, 82% at 600 ms, and 93% at 800 ms. The recovery curves show that our patient recovered significantly faster than control subjects (p = 0.046, Student's t-test). SRFM is a nocturnal motor phenomenon, familiar or sporadic (Vetrugno et al., 2002), characterized by myoclonic jerks, isolated or in cluster, involving the muscles innervated by the fifth and seventh cranial nerves (Loi et al., 2007), that should be differentiated from nocturnal bruxism (Vetrugno et al., 2002). In our case, SFRM went undiagnosed for a long period of time because TB was considered a sign of nocturnal epileptic seizures, despite the fact that the seizures were never directly witnessed. Sleep-related paroxysmal motor phenomena involving the orofacial and masticatory muscles have a wide spectrum of causes, including epileptic seizures, sleep disorders, sleep-related movement disorders, and psychiatric disturbances (Tinuper et al., 2007), and it may be difficult to distinguish them clinically. The nocturnal video-polisomnography is therefore of key importance to reach a precise diagnosis. In our opinion, the association between SFRM TB, and a significantly faster recovery of the blink-reflex R2 component (possibly due to a hyperexcitability of brainstem interneurons), suggest a subcortical origin of the jerks as reported in other movement disorders (Carella et al., 1994). We conclude that SRFM should be considered in the differential diagnosis of sleep-related seizure disorders in the presence of frequent TB episodes unresponsive to antiepileptic drugs. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this letter is consistent with those guidelines. We have no conflicts of interest to disclose.