Background: Multiple sclerosis (MS) patients often suffer from fatigue.
Objective: We evaluated the relationship of obstructive sleep apnea to fatigue and sleepiness in MS patients.Methods: Ambulatory MS patients without known sleep disorders and healthy controls underwent diagnostic polysomnography and a multiple sleep latency test (objective sleepiness measure). Fatigue was measured with the Fatigue Severity Scale (FSS) and the Multidimensional Fatigue Inventory (MFI), and subjective sleepiness by Epworth Sleepiness Scale. Covariates included age, sex, body mass index, Expanded Disability Status Scale (EDSS), depression, pain, nocturia, restless legs syndrome, and medication.
Results: OSA (apnea-hypopnea index ≥15) was found in 36 of 62 MS subjects and 15 of 32 controls. After adjusting for confounders, severe fatigue (FSS ≥5) and MFI-mental fatigue (>group median) were associated with OSA and respiratory-related arousals in MS, but not control subjects. Subjective and objective sleepiness were not related to OSA in either group. In a multivariate model, variables independently associated with severe fatigue in MS were severe OSA [OR 17.33, 95% CI 2.53-199.84], EDSS [OR 1.88, 95% CI 1.21-3.25], and immunomodulating treatment [OR 0.14, 95% CI 0.023-0.65].
Conclusions: Obstructive sleep apnea was frequent in MS and was associated with fatigue but not sleepiness, independent of MS-related disability and other covariates.