An Underrecognized Comorbidity: Restless Legs Syndrome Drives Fatigue in Pulmonary Sarcoidosis Independent of Mood

Abstract Purpose Under strict differential-diagnosis criteria, restless legs syndrome (RLS) prevalence is estimated at 1.9–4.6% among adults (approximately 3.2–3.4% in Turkish population surveys), while broader symptom-based case definitions yield estimates of 5–15%; RLS has also been linked to several cardiovascular, metabolic, and neurological comorbidities. Given the high prevalence of fatigue and sleep disturbances in sarcoidosis, this study aimed to determine RLS prevalence in sarcoidosis patients and its association with fatigue and mood disturbances. Methods Sarcoidosis patients diagnosed by radiological and histopathological criteria completed standardized questionnaires; RLS was diagnosed using International Restless Legs Syndrome Study Group (IRLSSG) criteria. Clinical, laboratory, and radiological data were retrospectively collected, and patients were stratified by RLS status. Fatigue, cognition, sleep quality, insomnia, anxiety, and depression were assessed using the Fatigue Severity Scale (FSS), Mini-Mental State Examination (MMSE), Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), Insomnia Severity Index (ISI), Pittsburgh Sleep Quality Index (PSQI), and Epworth Sleepiness Scale (ESS). Results RLS was present in 34 patients (35.1%); 72.2% were female, mean age 45.12 ± 11.02 years. No significant intergroup differences emerged in age, sex, anthropometrics, or cognition. RLS patients showed significantly higher fatigue, depression, and anxiety scores (p = 0.002, p < 0.001, p < 0.001), while sarcoidosis stage and Modified Medical Research Council (MMRC) dyspnea scores did not differ (p = 0.135). Only IRLSSG severity (p = 0.040) and MMRC (p = 0.001) remained independent fatigue predictors. Conclusions RLS is markedly more prevalent in sarcoidosis, with fatigue independently associated with RLS severity and dyspnea burden rather than mood, suggesting RLS is an underrecognized, modifiable contributor warranting screening.