Background and purpose: Although an essential diagnostic feature of restless legs syndrome (RLS) is the presence of circadian symptom variations, with an increase in the evening or at night, the mechanisms underlying this time-bound variation remain unknown. Since dopaminergic mechanisms seem to play a central role in the pathophysiology of RLS, it is likely that circadian variations in the dopaminergic system or factors affecting it cause the nightly increase. The reverse is also possible; dopaminergic medication might affect melatonin function, a key element of the circadian system. The present study investigated the effects of dopaminergic medication on melatonin secretion in RLS.
Patients and methods: Eight previously untreated patients diagnosed with idiopathic RLS underwent a three-week, open-labeled treatment with 400 mg L-DOPA (+100 mg CarbiDOPA). Dim Light Melatonin Onset (DLMO), a marker of circadian phase, was determined before and after treatment.
Results: Compared to baseline, earlier DLMO was found in L-DOPA treated patients (21:00+/-1:20 vs. 18:50+/-0:55; P < 0.05). Anticipation of DLMO was more marked in the subgroup of patients showing augmentation. A positive correlation was observed between change of DLMO, sleep latency and time of onset of symptoms following treatment with L-DOPA.
Conclusions: Our results suggest that L-DOPA may exert chronobiotic effects in RLS.