The polysomnographic diagnosis of REM sleep behavior disorder: to change or not to change, that is the question

This is the authors' abstract. We don't add key points for this paper.

Dear Editor, In recent years, REM sleep behavior disorder (RBD) has been the focus of a continuously growing number of articles [1], including the increased attention to identifying the most promising biomarkers in forecasting its phenol conversion from isolated RBD (iRBD) to a neurodegenerative disorder [2]. This rich body of literature is based on data from patients diagnosed in accordance with the criteria set forth in the International Classification of Sleep Disorders 3rd edition (ICSD-3) [3]. The polysomnographic (PSG) demonstration of REM sleep without atonia (RSWA) is one of the required criteria for the diagnosis of RBD in the ICSD-3. This calls attention to the necessary objective role played by the PSG in evaluating patients with suspected RBD. For this reason, we have read with interest the recent guidelines proposed by members of the International RBD Study Group (IRBDSG) for the video-PSG procedures needed to diagnose RBD that were published in SLEEP [4]. These guidelines were believed to be necessary in order to fill gaps in the current ICSD-3 diagnostic criteria that, in the authors’ opinion, needed to be filled and included recommendations on video-PSG technical settings; REM sleep staging; scoring of RSWA; methods for the analysis of video and audio recordings; video-PSG guidelines for the diagnosis of RBD; and the identification of its neurodegenerative prodromal stages. The authors also clearly state that their recommendations are intended for both practicing clinicians and researchers, including the assessment of REM sleep motor events, RBD behavioral episodes, and vocalizations for research purposes only. The authors conclude that their guidelines will ensure the collection of homogeneous objective data, favoring future multicenter studies and clinical trials. Among the most impactful novel requirements of these guidelines, with respect to the ICSD-3 [3] criteria that only require the PSG demonstration of RSWA, is the need to obtain at least one video-PSG recording in which a clear RBD behavioral episode occurs. It is common knowledge that capturing an RBD behavioral event during video-PSG can be difficult and thus this approach would imply the probable need for repeated video-PSG recordings, in cases where a RBD behavioral episode does not occur during the first recording night, none of which may be reimbursable by health insurance. For example, among 72 recordings of patients with iRBD (65 males and seven females, aged 53.1–83.1 years, diagnosed at the Sleep Research Centre of the Oasi Research Institute—IRCCS, Troina, Italy) for whom the RBD severity scale (RBDSS) [5] score was available, 20 had a score of 0 (“no visible movement”), 28 had a score of 1 (“slight movements or jerks”) and 24 a score of 2 or 3 (“movements involving proximal extremities, including violent behavior” or “axial involvement including bed falls”). This indicates that only one third of patients might be presenting a clear-cut behavioral episode during a single video-PSG recording. If we consider those with a score of 1 and the presence of vocalizations, the number increases to 43, which still means that about 40% of patients do not show a clear behavioral episode during a single night recording. We must keep in mind that guidelines put forth by an international organization, such as the IRBDSG, should be first of all feasible and able to be applied in most, if not all, the countries and socioeconomic environments. However, a series of concerns arises when reading the various recommendations published by Cesari et al. [4], which were not taken into account by the authors: Do most sleep labs in all countries have a sleep technologist in attendance all night during PSGs? Is there sleep technologist certification in all countries? If there is no sleep technologist certification in a country, then what is the training background/clinical experience for sleep technologists in that country (courses in neurophysiology/EEG technology, in respiratory medicine and mechanical ventilation, or trained by the sleep doctor when they start to work at the sleep lab)? Is there public/private health insurance coverage for PSG studies (including the chin EMG, EEG, EKG, respiratory monitoring) needed to diagnose RBD in all countries? Does health insurance cover in-lab PSG studies with the stated indication of “Suspected RBD” or is another diagnosis is needed, such as “Suspected OSA” or “Suspected nocturnal seizures”? Does health insurance only cover home (unattended) PSG studies for RBD? Does health insurance cover a second PSG study? If yes, in which cases? (One indication would be if there is comorbid OSA that needs treatment with CPAP, and then a second PSG study would confirm, or not confirm, the diagnosis of RBD. Is video used during PSG studies for RBD in all countries? Are PSG machines with sufficient specification to record and analyze RSWA available in all countries? All these considerations refer to specific and practical implications of the guidelines by Cesari et al. [4] and appear to represent a clear obstacle to their implementation across clinical practice. The obvious consequence of this problem is that if the proposed guidelines are endorsed by the health systems and the medical community across the world, the application of these guidelines would strongly interfere with the diagnosis of RBD in a large portion of patients who would not be able to receive the required (often repeated) video-PSG evaluation. Furthermore, the delay in making the diagnosis of RBD may also delay the initiation of therapy of patients at risk for injurious, and potentially life-threatening, dream-enacting behaviors [6, 7]. Moreover, the application of these rigorous guidelines to the research arena is also not risk-free. Indeed, while we do agree that these guidelines would allow the identification of patients with a clear-cut and homogenous diagnosis of RBD, a substantial number of research studies would not be sponsored by the academic and commercial funding agencies given the limited budgets (that are often the case). Thus, an unintended consequence of these guidelines might in fact be the restriction of future RBD research studies. Similarly, sponsored clinical trials, which are definitely needed studies [8], might become more expensive with the endorsement of all these guidelines, which would be likely to limit the number of eligible patients and reduce the pool of who could be enrolled. The final effect is most probably the slowing of the advancement of the knowledge of RBD and its heralding of evolving neurodegeneration. In conclusion, we believe that while reconsiderations related to diagnosis and optimal procedures should be encouraged, they need to be balanced against clinical and research feasibility. In the best of all possible scenarios, the guidelines proposed by Cesari et al. [4] would be welcomed, but the real-world limitations described above need to be considered. Therefore, we believe that the current ICSD-3 [3] criteria should be still kept as the reference for the diagnosis of RBD and that further discussions among members of the IRBDSG take place to ensure the feasibility of any changes (four of the authors of this letter are members of the IRBDSG). Clearly, where funding allows, the guidelines proposed by Cesari et al. [4] should first be applied across multiple centers to determine their further utility. Raffaele Ferri: no relevant COI; Simon J.G. Lewis: NHMRC Leadership Fellow (#1195830); consultancy fee Pharmaxis Ltd.; Naoko Tachibana: no relevant COI; Clete A. Kushida: no relevant COI; Carlos H. Schenck: one-lecture lecture honorarium, Eisai, Inc.