Circadian changes in CSF dopaminergic measures in restless legs syndrome

BACKGROUND AND PURPOSE: Restless legs syndrome (RLS) has a circadian component with symptoms being prominent at night. The dopaminergic (DAergic) system, which plays a role in RLS, entails circadian changes that parallel RLS symptom changes. The aim of this study was to look for relative and diurnal differences in DAergic activity. PATIENTS AND METHODS: All RLS subjects were treated prior to their enrollment in the study but were all drug-free for at least 2 weeks prior to evaluation. Cerebrospinal fluid (CSF) collected at 10 p.m. was used to determine DA-related co-factors and metabolites. These were compared to CSF values collected in a previous study at 10 a.m. RESULTS: The only significant finding from the 10 p.m. samples (30 RLS; 22 control) was increased 3-ortho-methyldopa (3OMD) for RLS compared to controls. A comparison of the 10 p.m. to 10 a.m. values (16 RLS; 9 controls) showed small, non-significant diurnal changes for controls but large diurnal changes in tetrahydrobiopterin (BH4), HVA:5HIAA ratio and 3OMD for RLS, with the 10 a.m. sample showing increases in all three CSF factors compared to the 10 p.m. sample. CONCLUSIONS: The greater diurnal changes in RLS suggest greater fluctuations than normal in DAergic circadian dynamics. The increased 3OMD concentration in the absence of concurrent exogenous levodopa (l-dopa) suggests changes in synthesis or metabolism of l-dopa in RLS.