A further evaluation of the cognitive deficits associated with restless legs syndrome (RLS)

BACKGROUND AND PURPOSE: Restless legs syndrome (RLS) is a common sensorimotor disorder that peaks in severity during the night and comes on with rest. As a result, this condition often results in significant chronic sleep loss, especially for those with severe disease. Chronic partial sleep restriction has been associated with conditions such as depression, anxiety, chronic pain, and decline in cognitive function. Furthermore, studies have found that RLS patients suffer from these conditions more than their unaffected peers. Thus, the morbidity rate associated with RLS has often been attributed to the chronic sleep loss that frequently accompanies this condition. However, no study has specifically compared RLS sufferers to otherwise normal sleep-restricted controls in order to assess disease morbidity independent of its sleep deprivation effects. In this study, we compared the cognitive function of RLS patients who were off treatment to sleep-restricted control subjects. SUBJECTS AND METHODS: A novel chronic partial sleep-restriction protocol that utilized a 14-day combined inpatient and outpatient design was implemented in order to test the differences in cognitive functioning between RLS patients and sleep-restricted controls. The brief cognitive battery included instruments assessing general intelligence and global executive function in order to control for baseline cognitive function between the groups, and then the effects of sleep loss were assessed using prefrontal lobe-specific tasks. The final sample consisted of 16 RLS (11 male and 5 female) and 13 sleep-restricted control subjects (7 male and 6 female). RESULTS: In order to examine the differences in cognitive functioning between sleep-restricted controls and RLS subjects, independent samples t-tests were conducted. RLS subjects performed significantly better on both the Letter Fluency (t=2.13, p<0.05) and Category Fluency (t=2.42, p<0.05) than sleep-restricted controls. CONCLUSIONS: RLS subjects performed better than the sleep-restricted controls on two tasks that are particularly sensitive to sleep loss. Although previous studies suggest that sleep deprivation may impact the cognitive function of those with RLS, our data suggests that RLS subjects may show a relative degree of sleep loss adaptation. Future investigations that more closely match the sleep loss pattern of RLS subjects to controls are warranted in order to explore these potential traits further.