Quantitative sensory test for primary restless legs syndrome/Willis-Ekbom disease using the current perception threshold test

Background: Restless legs syndrome/Willis-Ekbom disease (RLS/WED) is a sensorimotor neurological disorder, and it is especially aggravated at night. The purpose of this study was to investigate the diurnal sensory dysfunction in primary RLS/WED using the current perception threshold (CPT) test, compared to healthy controls.

Methods: Thirty primary RLS/WED subjects and 30 healthy controls were enrolled. The severity of RLS/WED and sleep problems were evaluated in all subjects. Peripheral polyneuropathy was excluded through neurological examination and nerve conduction study. We used the Neurometer^® system for the CPT test and applied three different parameters (2000 Hz, 250 Hz, and 5 Hz), to stimulate both big toes. The CPT test was performed twice, once during the asymptomatic daytime period and again in the evening, when the patients were symptomatic.

Results: The mean ages of the RLS/WED group and controls were 50.5 ± 11.7 (22; 73.3% female), and 46.3 ± 11.4 (24; 80.0% female), respectively. The mean international RLS/WED study group severity scale score was 28.6 ± 4.25. There was no significant difference in the current perception thresholds between the RLS/WED patients and controls in daytime. However, the RLS/WED patients had lower mean CPT measurements for all three stimulation protocols in the evening (2000 Hz: 393.2 ± 93.7 vs 430.8 ± 79.6, 250 Hz: 172.0 ± 48.4 vs 198.5 ± 38.2, and 5 Hz: 98.0 ± 34.1 vs 124.6 ± 31.3), while the healthy controls showed no difference.

Conclusions: RLS patients showed a lower CPT in the evening. The diurnal variation of hyperalgesia in RLS/WED patients indicates a central (circadian) sensory processing disturbance rather than a peripheral disturbance.