Periodic Limb Movements during Sleep in Idiopathic REM Sleep Behavior Disorder: A Systematic Review and Meta-Analysis

Background Idiopathic/isolated REM sleep behavior disorder (iRBD) serves as a prodromal marker for alpha-synucleinopathies, with most patients developing neurodegenerative disease over time. The prevalence and clinical significance of concurrent periodic limb movements during sleep (PLMS) in iRBD remain poorly understood, despite shared brainstem pathophysiology that could inform clinical phenotyping. Methods We conducted a systematic review and meta-analysis of PLMS prevalence in iRBD, searching PubMed, Embase, and Cochrane Library for studies reporting PLMS in polysomnographically confirmed iRBD. Three studies comprising 312 patients from Canada, Japan, and Italy were analyzed using random-effects modeling. Results PLMS prevalence varied by diagnostic threshold: 60% at ≥20 events/hour and 33-48% at ≥15 events/hour. Meta-analysis yielded a pooled prevalence of 46% (95% CI: 33-60%; I²=79%). Paradoxically, in one study of 81 patients, iRBD patients with PLMS demonstrated reduced daytime sleepiness despite elevated PLMS indices, and PLMS were significantly associated with REM sleep without atonia; in a separate study of 191 patients, PLMS was associated with improved executive function despite poorer sleep quality. These secondary findings derive from single studies and were synthesized narratively rather than pooled statistically. Conclusions The pooled PLMS prevalence in iRBD was 46% (95% CI: 33-60%), higher than rates previously reported in general populations, though age-matched comparisons were not performed. Paradoxical clinical associations warrant cautious interpretation given small sample sizes and methodological limitations. Current evidence supports PLMS documentation during routine polysomnography for research and longitudinal tracking but does not justify clinical intervention.