Abstract
Restless legs syndrome (RLS) is characterized by unpleasant sensations generally localized to legs, associated with an urge to move. A likely pathogenetic mechanism is a central dopaminergic dysfunction. The exact role of pain system is unclear. The purpose of the study was to investigate the nociceptive pathways in idiopathic RLS patients. We enrolled 11 patients (mean age 53.2 ± 19.7 years; 7 men) suffering from severe, primary RLS. We recorded scalp laser-evoked potentials (LEPs) to stimulation of different sites (hands and feet) and during two different time conditions (daytime and nighttime). Finally, we compared the results with a matched control group of healthy subjects. The Aδ responses obtained from patients did not differ from those recorded from control subjects. However, the N1 and the N2-P2 amplitudes' night/day ratios after foot stimulation were increased in patients, as compared to controls (N1: patients: 133.91 ± 50.42%; controls: 83.74 ± 34.45%; p = 0.016; Aδ-N2-P2: patients: 119.15 ± 15.56%; controls: 88.42 ± 23.41%; p = 0.003). These results suggest that RLS patients present circadian modifications in the pain system, which are not present in healthy controls. Both sensory-discriminative and affective-emotional components of pain experience show parallel changes. This study confirms the structural integrity of Aδ nociceptive system in idiopathic RLS, but it also suggests that RLS patients present circadian modifications in the pain system. These findings could potentially help clinicians and contribute to identify new therapeutic approaches.
Highlights
Idiopathic restless legs syndrome (RLS) is a large prevalent chronic sensory-motor disorder [1] and it is characterized by unpleasant sensations generally localized to legs and associated with an urge to move. e etiology of RLS is not fully understood. e most likely pathogenic mechanism consists in a central dopaminergic dysfunction. e symptoms worsen or are exclusively present at rest [1]
In the RLS group, compared to controls, we found a significant increase of visual analog scale (VAS) score after foot and hand stimulation during night session
Discussion e Aδ-fiber responses recorded after foot and hand stimulation in all our patients did not differ from those obtained in control subjects. is result suggests that RLS patients do not have a small fiber neuropathy
Summary
Idiopathic restless legs syndrome (RLS) is a large prevalent chronic sensory-motor disorder [1] and it is characterized by unpleasant sensations generally localized to legs and associated with an urge to move. e etiology of RLS is not fully understood. e most likely pathogenic mechanism consists in a central dopaminergic dysfunction. e symptoms worsen or are exclusively present at rest [1]. Idiopathic restless legs syndrome (RLS) is a large prevalent chronic sensory-motor disorder [1] and it is characterized by unpleasant sensations generally localized to legs and associated with an urge to move. Involvement of nociception in RLS is suggested by the therapeutic response to opioids and the physiologic link between dopamine and pain control [5]. In patients with RLS, both primary and secondary to large fiber neuropathy, Schattschneider et al found an impairment of thermal perception threshold suggesting a small fiber involvement [6]. Another study [7] demonstrated that symptomatic RLS may be triggered by small fiber neuropathy. E lower pain threshold in RLS patients than in control suggests that pain processing may be amplified in this disease [8]. Hyperalgesia associated with tactile hypoesthesia and paradoxical heat sensation was described in RLS patients [9]
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