The effect of comorbid medical diagnoses on disturbed sleep in chronic fatigue syndrome

Abstract

ABSTRACT Background Chronic fatigue syndrome [CFS] may occur alone or with fibromyalgia. This has led some to believe the two occur along a common illness spectrum. Evaluating whether this is the case is important as differences in burden or severity of CFS with fibromyalgia (FM) would suggest different underlying pathophysiological processes. Objective To determine if Insomnia Severity Index [ISI] scores differ between patients with CFS and those with CFS plus FM. In addition, we aim to determine if insomnia severity is impacted by other comorbid medically unexplained diagnoses. Methods 247 patients with CFS completed the ISI and the Centers for Epidemiological Study – Depression. Patient groups were stratified on CFS severity and the presence of FM. A secondary analysis was conducted to evaluate insomnia severity related to the number of comorbid medically unexplained diagnoses including, FM, multiple chemical sensitivity and/or irritable bowel syndrome. Results When controlling for depressed mood, ISI did not differ significantly across patient groups defined by CFS severity and FM status. However, independent of mood, ISI was sensitive to multiple diagnoses showing a significant increasing trend from CFS alone to CFS plus one, two or three comorbid diagnoses. Conclusion Although CFS severity and FM status do not impact insomnia severity, increased illness burden as manifested by multiple medically unexplained diagnoses does appear to influence insomnia. In contrast to our earlier studies, this study did not find that a comorbid diagnosis of FM in patients with CFS is related to a worse outcome in the variable of interest.