Evaluating daytime alertness in individuals with Restless Legs Syndrome (RLS) compared to sleep restricted controls

Restless Legs Syndrome (RLS) is a common sensorimotor disorder often associated with significant chronic sleep loss. Previous studies looking at the effects of sleep loss on daytime function in RLS individuals, using subjective reporting techniques have yielded mixed results. In this study we used more objective measures of alertness and compared RLS subjects who are off treatments and chronically sleep restricted to chronic sleep-restricted controls.

The final sample consisted of 20 RLS subjects (10 male and 10 female) and 13 sleep-restricted controls (seven male and six female). Thirteen controls underwent a 14-day chronic partial sleep-restriction protocol in order to closely match the degree of chronic sleep loss reportedly experienced by untreated RLS patients. On the final day of the protocol each subject performed a morning and evening Suggested Immobilization Test (SIT) which served as a modified Maintenance of Wakefulness Test (MWT). RLS and control groups were compared for differences in alertness as measured objectively by the sleep latency on the morning and evening SITs.

The RLS subjects had a longer sleep latency on the morning and evening SIT than controls (t=3.80, p=0.001, U=31.0, p<0.001, respectively). Even after controlling for the potential arousal impact associated with increased leg activity, RLS individuals still demonstrated a higher degree of objective alertness (p=0.023, p=0.006, Fisher's exact test).

RLS subjects, despite having, if anything, greater sleep loss, displayed greater sustained alertness than sleep-restricted controls. Thus, the heightened degree of alertness demonstrated by RLS patients may be in contrast to the perceived impairment in mood, vigor, and vigilance commonly reported in previous studies.