Restless legs syndrome (RLS) is characterized by an urge to move that occurs in the evening or night time, suggesting circadian involvement. However, objective evidence regarding the circadian phase in RLS remains limited, particularly in real-world settings. We conducted an exploratory pilot study to investigate circadian rhythm timing in patients with RLS using actigraphy-based dim light melatonin onset (DLMO) estimation and to explore its potential association with symptom severity. Patients with idiopathic RLS (n = 21) and age- and sex-matched chronic insomnia controls (n = 21) underwent 14 days of wrist actigraphy to assess rest-activity rhythms and obtain estimated DLMO (eDLMO) from an actigraphy-based mathematical model. Symptom severity was evaluated with the International RLS Study Group rating scale (IRLS). Group comparisons and correlation analyses were conducted in an exploratory manner given the sample size. Patients with RLS (mean age 61.2 ± 7.7 years, 90% female) demonstrated a non-significant trend toward delayed eDLMO compared with insomnia controls (mean age 61.7 ± 7.1 years, 90% female; 10:01 PM ± 47 min vs 9:33 PM ± 49 min, p = 0.069, Cohen's d = 0.58). Within the RLS group, higher IRLS scores were modestly associated with later eDLMO (β = 0.0726, p = 0.038), after adjusting for age and depressive symptoms. In contrast, eDLMO was not significantly associated with Insomnia Severity Index (ISI) or Pittsburgh Sleep Quality Index (PSQI) scores in the insomnia control group. In this exploratory pilot study, patients with RLS showed a tendency toward delayed estimated circadian phase compared with insomnia controls, and later estimated circadian phase was modestly associated with greater RLS symptom severity. These findings support a possible link between circadian phase delay and clinical burden in RLS but require confirmation in larger studies.
