1174 Oromandibular/Faciomandibular Myoclonus; A Rare Sleep-Related Movement Disorder Captured on Polysomnography

Introduction Oromandibular myoclonus (OMM) also known as faciomandibular myoclonus (FMM) is a rare neurological sleep-related movement disorder characterized by involuntary and repetitive contractions of the facial muscles. Consequences of this disorder include nocturnal tongue and cheek biting, which can mimic signs of seizure disorders. This case report presents a patient with OMM/FMM which was captured on polysomnography. Report of case(s) The patient is a 25-year-old male with a medical history that includes hypertension, obesity (BMI 67), bipolar disorder, and headaches. He presented with the chief complaint of excessive daytime sleepiness. He also endorsed waking up with a sore tongue on nearly a monthly basis without obvious reason. He underwent a split-night polysomnogram with transcutaneous CO2 (TcCO2) monitoring which showed severe obstructive sleep apnea (apnea-hypopnea index of 114.6) and sleep related hypoventilation with TcCO2 levels greater than 55 mm of Hg for more than 10 consecutive minutes. During the titration portion of the polysomnogram, several very brief (less than 250 milliseconds) stereotypical jerk-like contractions of his jaw muscles with characteristics of myoclonus were observed during REM sleep. These occurred as isolated bursts and clusters of irregular bursts of three to five repetitive contractions. Increased amplitude in the submentalis EMG leads, as well as muscle artifact in the EOG and EEG channels were identified during events. EEG showed no epileptiform findings. REM sleep atonia was otherwise preserved. Conclusion Oromandibular/Faciomandibular myoclonus is a sleep-related movement disorder characterized by very brief (less than 250 milliseconds) forceful myoclonus of masticatory muscles in sleep. These can occur either as isolated bursts or as a cluster of regularly or irregularly occurring brief bursts. Pathophysiology is considered to be a form of brainstem reticular myoclonus, involving a circuitry of cranial nerve V and VII nuclei along polysynaptic pathways. Tongue biting is widely recognized as a useful clinical diagnostic tool for differentiating between epileptic seizures and nonepileptic events. OMM/FMM typically presents with recurrent nocturnal tongue biting, which can be misdiagnosed as nocturnal seizures. Therefore, appropriate awareness and recognition is important to avoid an epilepsy misdiagnosis which may result in lifelong anti-seizure medication use. Support (if any)