Is restless legs syndrome associated with chronic mountain sickness?

• Limbo subjects had the highest restless legs syndrome (RLS) severity score.
• Chronic mountain sickness (CMS) subjects had the lowest oxygen saturation and the highest hematocrit values.
• O2 saturation, sleep quality, and Quinghai score of >5 were associated with RLS.
• RLS could be an early clinical manifestation of hypoxia at high altitudes.
• High-altitude dwellers could be a good model to study the role of hypoxia in RLS.

BackgroundRestless legs syndrome (RLS) and chronic mountain sickness (CMS) share physiological traits. Our objective was to explore a possible association between RLS and CMS.MethodsWe carried a cross-sectional study with male subjects living between 4100 and 4300 m above sea level. Participants underwent a clinical interview, physical examination, electrocardiographic (EKG) recording, and spirometry. We classified subjects into CMS, Limbo, and healthy high-altitude dwellers (hHAD), according to their Quinghai score and hematocrit levels. We applied the “Paradigm of questions for epidemiological studies of RLS,” The International Restless Leg Syndrome Study Group Scale, and the Pittsburgh Sleep Quality Index. Logistic regression analysis was used to determine the association between variables.ResultsSeventy-eight male subjects were included. Forty subjects were hHAD, 23 were CMS patients, and 15 participants were considered as Limbo. CMS and Limbo subjects had a higher frequency of RLS (p < 0.05). Limbo subjects had the highest severity score for RLS. There were no differences in age, body mass index (BMI), or tobacco use between RLS patients and non-sufferers. In the multivariate analysis, CMS was not associated with RLS diagnosis. Oxygen saturation (p = 0.019), poor sleep quality (p < 0.01), and Quinghai score of ≥6 (p = 0.026) were independently associated with RLS diagnosis.ConclusionsOur results did not show a direct association between RLS and CMS; however, RLS was associated with reduced oxygen saturation. Hence, RLS could represent an early clinical manifestation of hypoxia, or, in CMS natural history, an early sign of maladaptation to high altitude.