Searching for Marker of REM Sleep Behavior Disorder: Submentalis Muscle EMG Amplitude Analysis During Sleep in Patients with Narcolepsy/Cataplexy

Abstract

WE FOUND THE ARTICLE BY FERRI ET AL.1 ON A POLYSOMNOGRAPHIC MARKER OF REM SLEEP BEHAVIOR DISORDER (RBD) VERY INTERESTING AS IT HIGHLIGHTS the importance of assessing for RBD among narcolepsy patients. Recent studies on narcolepsy show that up to 60% of patients report RBD symptoms, and 43% had an RBD episode during video-polysomnography.2 Notably in the pediatric narcolepsy population, RBD is under-recognized.3 We did not identify RBD in a single child with narcolepsy/cataplexy.4 This may be related to inadequate screening questions asked during the initial evaluation of patients with narcolepsy/cataplexy to rule out RBD. Ferri et al. used quantitative and computerized methods of analysis of the EMG signal and found significant polysomnographic signs of motor dyscontrol among patients with narcolepsy compared to controls. Using the REM Sleep Atonia Index, 38% of patients with narcolepsy/cataplexy were found to have REM without atonia (RWA). This altered RWA index in patients with narcolepsy/cataplexy was largely related to increase in short lasting EMG activity which may differentiate RBD in patients with narcolepsy/cataplexy from those with idiopathic/symptomatic RBD. These results provide a tool to detect subclinical RBD, which is especially useful in the pediatric narcolepsy population, where history may be unreliable. Future research will be needed to develop a consensus about the accurate diagnosis of RBD, especially in patients with narcolepsy/cataplexy. More importantly, RBD can cause significant nocturnal sleep dysfunction in patients with narcolepsy/cataplexy, and recognition of this comorbid disorder can also guide treatment choices. Selective serotonin reuptake inhibitors (SSRIs) have been recently used as first-line treatment of cataplexy in patients with narcolepsy. Both SSRIs and tricyclic antidepressants have been associated with worsening of, or precipitating symptoms of RBD.5 It is important to differentiate whether the treatment of narcolepsy/cataplexy with these medications may contribute to development of RBD in this population, or if RBD exists de novo in patients with narcolepsy/cataplexy. Though it has not been adequately studied, it is possible that a noradrenergic drug such bupropion would be a better suited medication in this situation, as its properties are likely more dependent on dopaminergic mechanisms, thus not worsening symptoms of RBD.5 Whether it treats cataplexy effectively needs to be further explored. In our own practice, SSRIs have been discontinued in narcoleptic patients with RBD symptoms, and sodium oxybate used to improve nocturnal sleep, daytime alertness, and cataplexy. Attempts to screen for RBD must be made in every new-onset patient with narcolepsy/cataplexy via directed questions. Consensus for appropriate treatment in this situation also needs to be developed.