Hyperdopaminergism in lenticulostriate stroke-related restless legs syndrome: an imaging study

The pathophysiology of restless legs syndrome (RLS) involves a dopaminergic dysregulation that remains poorly understood, with controversial data from the literature. Stroke-related RLS is a rare condition that involves primarily the basal ganglia, the paramedian pons, and the thalamus. Given these elements, we studied dopaminergic metabolism in patients with RLS secondary to lenticulostriate infarction using structural and nuclear imaging in the striatum ipsilateral to the infarction area, as compared to the contralateral side. We hypothesized that dopaminergic metabolism would be impaired in the striatum ipsilateral to stroke.

In this observational case-control study, we aimed to prospectively include patients with RLS secondary to lenticulo-striate infarction, for analyses of dopamine dysfunction ipsilateral to stroke as compared to the contralateral striatum and to a control population. Four patients fulfilled inclusion criteria with either de novo RLS or major exacerbation of RLS existing prior to stroke, and all four patients were included. Structural imaging was performed using brain magnetic resonance imaging, and the stroke-induced metabolic modifications were assessed by ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET). Dopamine reuptake via DAT was explored using ¹²³I-FP-CIT SPECT. PET with ¹⁸F-FDOPA was used to evaluate the functional integrity of the presynaptic dopaminergic synthesis.

The only structure damaged in all patients was the body of the caudate nucleus, right-sided for three and left-sided for one, as illustrated by magnetic resonance imaging. ¹⁸F-FDG PET showed a hypometabolism in the infarcted area, the ipsilateral thalamus, and the contralateral cerebellum. All patients displayed, in the ipsilateral putamen, increased dopaminergic tone.

The present findings suggest that increased dopaminergic tone in the striatum may participate in the pathogenesis of RLS. These observations should encourage further research on RLS symptomatic with well-defined lesions as a promising way to further improve our understanding of its pathophysiology.