Electrophysiologic disturbances during daytime in patients with restless legs syndrome: Further evidence of cognitive dysfunction?

Backgrounds: It has been reported that patients with restless legs syndrome (RLS) may have cognitive deficit. The authors performed EEG and ERP analysis during daytime to identify electrophysiologic relations with cognitive dysfunction in unmedicated RLS patients. Methods: Seventeen drug naive RLS patients (53.7 ± 9.6 years) and 13 age-matched healthy controls participated in the present study. EEG was recorded during the waking-resting state and during a visual oddball task. RLS severities were determined using the International RLS Severity Scale. Stanford sleepiness scale (SSS) and bothersomeness visual analog scale (VAS) scores were determined immediately after ERP sessions. EEG power spectra and P300 amplitude and latency were compared for patients and controls. Clinical variables were correlated with P300 findings. Results: Waking-resting EEG showed that RLS patients had significantly higher beta activity in frontocentral regions than controls. SSS scores were not different in the two groups. But the bothersomeness VAS scores of RLS patients were significantly higher than those of controls. Furthermore, P300 latency was significantly longer in patients, and patients had significantly lower P300 amplitudes in frontal and central locations. In addition, P300 latency was found to be significantly correlated with bothersomeness during the ERP test, whereas P300 amplitude showed no such tendency. Conclusions: Our study supports the notion that RLS patients have an underlying cognitive dysfunction. Significant correlations found between P300 latency and bothersomeness, a lack of sleepiness during the ERP test, and increased beta activity in resting state EEGs suggest that a combination of inattention and cortical dysfunction underlie cognitive dysfunction in RLS.