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Validation of the RBD Symptom Severity Scale in the North American Prodromal Synucleinopathy Consortium
Parichita Choudhury1, Joyce K Lee-Iannotti1, Andrea O Busicescu1
1From the Cleo Roberts Memory and Movement Clinic (D.S., P.C.), Banner Sun Health Research Institute, Sun City; Division of Neurology (J.K.L.-I.) and Division of Neurology, Sleep Disorders Center (P.R.), Banner University Medical Center, Phoenix; College of Medicine (A.O.B.), University of Arizona, Tucson; Neurophysiology Unit (M.L.F.), Neurology Department, Clermont-Ferrand University Hospital, Institut Pascal, CNRS, Université Clermont Auvergne, France; Department of Neurology (A.Y.A.), University of California Los Angeles; Department of Neurology (D.L.B., D.E.H.), Emory University School of Medicine, Atlanta, GA; Department of Neurology (S.R.C., J.M., Y.-E.S.J.), Washington University School of Medicine, St. Louis, MO; Department of Neurology (E.H.D., M.G.M.), Stanford University; Department of Neurology (J.E.E., M.M.L.), VA Portland Health Care System and Oregon Health & Science University; Department of Psychiatry and Psychology (J.A.F.), Mayo Clinic, Rochester, MN; Department of Psychology (J.-F.G.), Université du Québec à Montréal, Canada; Department of Neurology (M.J.H., C.H.S.), University of Minnesota Medical Center, Minneapolis; Center of Sleep Sciences (E.M.), Stanford University, CA; Research Institute of the McGill University Health Centre (A.P.), Montréal; Center for Advanced Research in Sleep Medicine (A.P.), Hôpital du Sacré-Coeur de Montréal, Québec, Canada; Department of Neurology (E.K.S.L., B.F.B.), Mayo Clinic, Rochester, NY; Department of Neurology (A.V.), Harvard Medical School, Boston, MA; and Department of Neurology (R.P.), McGill University, Montréal, Canada.
Background And Objectives:
REM sleep behavior disorder (RBD) is a parasomnia characterized by dream enactment. The International RBD Study Group developed the RBD Symptom Severity Scale (RBDSSS) to assess symptom severity for clinical or research use. We assessed the psychometric and clinimetric properties of the RBDSSS in participants enrolled in the North American Prodromal Synucleinopathy (NAPS) Consortium for RBD.
Methods:
NAPS participants, who have polysomnogram-confirmed RBD, and their bedpartners completed the RBDSSS (participant and bedpartner versions). The RBDSSS contains 8 questions to assess the frequency and severity/impact of (1) dream content, (2) vocalizations, (3) movements, and (4) injuries associated with RBD. Total scores for participant (maximum score = 54) and bedpartner (maximum score = 38) questionnaires were derived by multiplying frequency and severity scores for each question. The Clinical Global Impression Scale of Severity (CGI-S) and RBD symptom frequency were assessed by a physician during a semistructured clinical interview with participants and, if available, bedpartners. Descriptive analyses, correlations between overall scores, and subitems were assessed, and item response analysis was performed to determine the scale's validity.
Results:
Among 261 study participants, the median (interquartile range) score for the RBDSSS-PT (participant) was 10 (4-18) and that for the RBDSSS-BP (bedpartner) was 8 (4-15). The median CGI-S was 3 (3-4), indicating moderate severity. RBDSSS-BP scores were significantly lower in women with RBD (6 vs 9, p = 0.02), while there were no sex differences in RBDSSS-PT scores (8 vs 10.5, p = 0.615). Positive correlations were found between RBDSSS-PT vs RBDSSS-BP (Spearman rs = 0.561), RBDSSS-PT vs CGI-S (rs = 0.556), and RBDSSS-BP vs CGI-S (rs = 0.491, all p < 0.0001). Item response analysis showed a high discriminatory value (range 1.40-2.12) for the RBDSSS-PT and RBDSSS-BP (1.29-3.47).
Discussion:
We describe the RBDSSS with adequate psychometric and clinimetric properties to quantify RBD symptom severity and good concordance between participant and bedpartner questionnaires and between RBDSSS scores and clinician-assessed global severity.
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