Underrecognized restless legs syndrome in Parkinson's disease: Diagnostic delay, association with sleep burden, and dopaminergic exposure in a Thai cohort.

PURPOSE: Restless legs syndrome (RLS) is a potentially treatable yet underrecognized contributor to sleep disturbance in Parkinson's disease (PD). The extent of missed diagnosis and its clinical implications in routine PD care remain unclear. We aimed to determine the prevalence of RLS, quantify diagnostic delay, and examine associations with sleep burden in a Thai PD cohort. METHODS: We conducted a cross-sectional study of consecutive patients with PD at a tertiary care center. RLS was diagnosed using International Restless Legs Syndrome Study Group (IRLSSG) criteria and confirmed by a specialist interview. Sleep burden was assessed using the Parkinson's Disease Sleep Scale-2 (PDSS-2) and the Pittsburgh Sleep Quality Index (PSQI). Multivariable logistic regression was used to identify factors associated with RLS. RESULTS: Among 250 patients with PD, 23.2% (95% CI, 18.4-28.8) met criteria for RLS. Notably, 95.8% of cases had not been previously diagnosed, with a mean diagnostic delay of 5.83 years. In multivariable analysis, higher PDSS-2 scores (adjusted OR 1.08, 95% CI 1.04-1.13) and higher levodopa equivalent daily dose (per 100 mg increase: adjusted OR 1.10, 95% CI 1.02-1.20) were independently associated with RLS. CONCLUSIONS: RLS is prevalent in PD but often goes unnoticed, leading to delayed diagnosis in routine clinical practice. Its presence strongly correlates with greater sleep disruption and increased use of dopaminergic medications. These results underscore the importance of systematically screening for and appropriately managing RLS in routine PD care. The study was registered on ClinicalTrials.gov (NCT06684782) on November 12, 2024. CLINICAL TRIAL: The study was approved by the Human Research Ethics Committee at Siriraj Hospital, Mahidol University (Si813/2024). STATEMENT OF SIGNIFICANCE: Nearly 25% of PD patients experience RLS, which is linked to poor sleep and higher doses of dopaminergic medications. Notably, 95.8% of these cases had not been diagnosed before, with an average delay of 5.83 years, indicating a significant gap in standard PD care and raising concerns. This research highlights how often RLS is overlooked in PD management, even within specialized clinics. PD patients with RLS had a higher motor burden, and 3.4% reported augmentation. These findings emphasize the importance of increasing clinical awareness and screening for RLS during routine PD visits, as well as developing a strategic approach to RLS in PD.