Symptom-related changes in current perception threshold of restless legs syndrome

Few studies have investigated the mechanisms responsible for the symptoms of restless legs syndrome (RLS). However, these studies were mainly performed during the asymptomatic period and therefore their findings might not apply to changes in sensory processing that occur during the symptomatic period. The objective of this study was to investigate the function of sensory nerve fibres in RLS patients using the current perception threshold (CPT) test during the daytime and in the presence of symptoms. Ninety-three patients with RLS and 34 healthy controls were included in the study. RLS patients were further divided into two subgroups, those who were experiencing RLS symptoms during the CPT test (symptom+) and those without symptoms (symptom-). Demographic data, RLS rating scale score and visual analogue scale were collected. Of the 127 enrolled subjects, CPT values were significantly lower in RLS patients than in controls for all three frequencies. Among the control and RLS subgroups (53 symptom+, 40 symptom-), symptom+ patients showed lower CPT values than controls. This finding indicates a relative hyperaesthetic state in the sensory afferents of peripheral nerves in symptom+ patients. There were no significant differences between the symptom- group and controls. The significantly lower CPT values for all three frequencies in symptom+ patients suggest that central sensory processing disturbance of sensory nerve fibres' input may be involved in the development of symptoms in RLS patients.