Adults with fibromyalgia (FM) have a higher incidence of restless legs syndrome (RLS), a finding that could ultimately result in improved sleep for those with the condition, according to a study published October 15 in the Journal of Clinical Sleep Medicine.

Five million American adults — up to 90% of them women — are diagnosed with FM, a chronic ailment characterized by widespread pain. Sleep difficulties, including nocturnal leg movements, are associated with FM.

RLS, a condition marked by an urge to move one's legs that often comes with an uncomfortable sensation deep within the legs, can also affect sleep. However, links between the 2 were previously established only by poor-quality studies.

"Our goals were to (1) investigate the prevalence of RLS in FM using a validated RLS screening tool, (2) estimate the strength of the association between RLS and FM, and (3) establish whether RLS disrupts sleep over and above the sleep disruption observed in FM patients," write Mari Viola-Saltzman, DO, from the Department of Neurology, Loyola University Medical Center, Maywood, Illinois, and colleagues.

The researchers examined 172 patients with FM who met the American College of Rheumatology diagnostic criteria for the condition, 93% of whom were women, all with a mean age of 50 years. Sixty-three patients free of pain and fatigue, 56% of whom were women, all with a mean age of 41 years, served as the control group. Participants self-reported RLS through a validated diagnostic telephone interview.

Prevalence and Odds for RLS Higher in Patients with FM

The results demonstrated that patients with FM had greater incidence and odds of RLS than those in the control group, as follows:

• the prevalence of RLS was significantly greater (33%) among those patients with FM (95% confidence interval [CI], 25.9 - 40.1) than in the control patients (3.1%; 95% CI, 0.0 - 7.4; P < .001), after adjustment for age and sex;
• the odds of RLS for those patients with FM, adjusted for age/sex, were 11.7 higher than for the control group (95% CI, 2.6 - 53.0; P < .01);
• the odds of RLS for those with FM were 11.2 (95% CI, 2.3 - 54.6; P < .01) after also adjusting for ethnicity and status for marriage, employment, education, and income; and
• the patients with FM had substantially higher scores than the control patients for all sleep measures — the Pittsburgh Sleep Quality Index (10.6 vs 4.5), Insomnia Severity Index (18.9 vs 12.1), and Epworth Sleepiness Scale (9.4 vs 5.7; P < .01 for all) — but subjective measures for limb pain were roughly the same for both groups.

The findings add another question to physician checklists for individuals with FM.

"Clinicians should routinely query FM patients regarding RLS symptoms because treatment of RLS can potentially improve sleep and quality of life in these patients," the authors write.

The study authors stated several limitations:

• RLS was determined by self-reporting and without in-person interviews,
• patients' medications that might cause RLS were not considered,
• other sleep disorders and underlying illnesses were not taken into account, and
• that the control group was free of fatigue may have biased it as having healthier overall sleep.

Because the study was cross-sectional in nature, further investigations are needed to explore causality.

"Future studies to investigate whether improvement in FM symptoms reduces RLS symptoms may be useful to further determine if FM is in fact a secondary cause of RLS," the authors write.

The National Institute of Arthritis and Musculoskeletal and Skin Diseases and the National Fibromyalgia Research Association supported the study. The study authors have disclosed no relevant financial relationships.

J Clin Sleep Med. 2010;6:423-427.

Nancy Fowler Larson • Medscape Medical News © 2010 WebMD, LLC