Validation of the International REM Sleep Behavior Disorder Study Group Symptoms Severity Scale (IRBD-SSS): a new tool to assess RBD clinical severity.

BACKGROUND

Currently, no standard scale has been validated to assess overall severity of RBD symptoms in the home environment. We aimed to evaluate the psychometric properties of the International RBD Severity Scale (IRBD-SSS), a new tool designed by the International RBD Study Group.

METHODS

Two versions of the IRBD-SSS were created, one for the patient (IRBD-SSS-PT) and another for the bedpartner (IRBD-SSS-BP), both consisting of 3 components, namely vocalizations, body movements and injury, with a fourth component (patient version only) evaluating dream content. To score each dimension, the frequency and severity/impact of behaviors during the previous month are multiplied. Psychometric properties of the IRBD-SSS were assessed, including reproducibility.

RESULTS

A total of 188 subjects including n = 132 RBD patients (n = 94 isolated RBD and n = 38 symptomatic RBD) and n = 52 bedpartners were enrolled from eight Sleep centers across France and Italy. Participants completed the scale at baseline and after one week. Acceptability of the scale was excellent in patients (97%) and bedpartners (98%). Internal consistency was acceptable for IRBD-SSS-PT (Cronbach α = 0.75) while slightly low for IRBD-SSS-BP (Cronbach α = 0.49). Concurrent validity was good for both patient (r = 0.70;p < 0.001, see Figure) and bedpartner (r = 0.69;p < 0.001) IRBD-SSS. Reproducibility was high for IRBD-SSS-PT (Lin's coefficient of agreement = 0.85 [0.81;0.90]) and good for the IRBD-SSS-BP (0.79 [0.68;0.90] (p < 0.001).

CONCLUSIONS

Both the patient and bedpartner versions of the IRBD-SSS showed excellent acceptability, acceptable internal consistency, good external validity and high reproducibility. IRBD-SSS is a useful tool to test the severity of RBD symptoms in clinical settings and clinical trials.

TRIAL REGISTRATION: NCT04071899.