An excerpt from the Summer 2016 edition of NightWalkers the Foundation's quarterly magazine. This piece is from the reoccurring column "In the News" by Lynn Marie Trotti, MD, MSc

Restless legs syndrome & depression: effect mediation by disturbed sleep and periodic limb movements.

Koo BB, et al. American Journal of Geriatric Psychiatry. April 2016.

Background:

Prior studies have shown that RLS and depression are associated, such that people with RLS are twice as likely as people without RLS to have depression at some point in their lives. The reason behind this relationship is not known, but a number of theories have been proposed (which are not mutually exclusive): 1) RLS and depression could share a common underlying cause; 2) depression medications may trigger RLS symptoms (which, in a cross-sectional study, could explain an association between depression and RLS); 3) sleep disruption from RLS could cause depression; or 4) periodic limb movements in sleep (PLMS) could cause depression. This study was designed to evaluate the latter three possibilities.

Research:

The researchers used data from the large Osteoporotic Fractures in Men (MrOS) study of elderly men, which has been used in multiple prior RLS studies. Included participants were evaluated for RLS and depression. Measures of PLMS and estimates of sleep quality were performed with in-home sleep studies and wrist actigraphy (a measure of activity), respectively. RLS was present in 17 percent of the 982 men. Those with moderate to severe RLS were most likely to be depressed, took the longest amount of time to fall asleep, had the most disrupted sleep, and had the greatest PLMS. The presence of moderate to severe RLS increased the likelihood of depression by about three times. Disrupted sleep accounted for some, but far from all, of the relationship between RLS and depression. Periodic limb movements moderated the depression-RLS relationship, such that people with RLS and PLMS had more depressive symptoms than those without RLS, but this effect was not seen in those with RLS without PLMS. People with RLS who were taking antidepressants had fewer depressive symptoms than people with RLS and depression who were not on medications.

Bottom Line:

The relationship between depression and RLS is mediated, in part but not exclusively, by the sleep disruption that accompanies RLS. The relationship between RLS and depression is apparent in those with PLMS, but not in those without PLMS. In people who are depressed, antidepressants are associated with fewer depression symptoms despite the presence of RLS (that is, having RLS does not appear to prevent an antidepressant benefit of medications).

New Questions:

Given that sleep disruption only partially explains the RLS depression relationship, what other factors are important?