Study Explores Sleepiness and Fatigue in CFS

A recent study led by Daniel Neu and published in the Journal of Sleep Research presented findings about the relationship between fatigue and sleepiness in people with chronic fatigue syndrome (CFS).

Fatigue, such as seen in CFS patients, and excessive daytime sleepiness, such as in sleep apnea–hypopnea syndrome (SAHS), remain poorly understood. Both daytime conditions are generally related to unrefreshing sleep and show affective symptoms. But to date, little scientific evidence has been gathered to determine whether CFS patients exhibit significant daytime sleepiness in addition to fatigue.  

This study compared 16 untreated CFS patients (mean age 32.8, all females) with 13 untreated SAHS patients (mean age 47.7, all females) and 12 healthy controls (mean age 32.2, all females). The patients exhibiting CFS (using the CDC diagnostic criteria) were selected from patients referred to a sleep laboratory. Investigators then employed further exclusion criteria in order to avoid overlaps with primary sleep disorders or psychiatric disorders.

All study subjects were free of neuropsychopharmacological treatment for at least 2 weeks prior to testing, and daytime napping, besides the sleep test, was not allowed in the sleep unit. All patients and controls filled out a sleep diary 2 weeks prior to testing to assess regular sleep–wake schedule, received a standard physical examination and a clinical review.

Then all study participants were admitted to a sleep unit for two consecutive nights of sleep testing including a polysomnogram (PSG). Multiple sleep latency tests (MSLT) that gauge how quickly and effectively a subject is able to fall asleep were carried out during the second day of the stay in the lab. Objective sleepiness was measured using the MSLT. Subjective sleepiness and fatigue were assessed with the Epworth Sleepiness Scale and the Fatigue Severity Scale, respectively.

Results indicated that mean sleep latency (length of time to fall asleep) on the MSLT was significantly shorter in SAHS patients than in CFS patients. Subjective sleepiness was greatest in SAHS patients and subjective fatigue was highest in CFS patients. Affective symptoms showed highest intensities in CFS patients.

While higher than the control group on all measures, compared to SAHS, the CFS group had higher subjective fatigue and lower subjective and objective sleepiness. These findings indirectly support the clinical distinction between fatigue and sleepiness, despite possible overlap in symptoms and signs of both daytime conditions.

One interesting descriptive polysomnographic finding was the high level of idiopathic microarousal index (MAI) in the CFS group—meaning small disturbances during the course of sleep. The MAI level found in CFS patients was almost as high as in the SAHS group. What is remarkable is that the CFS patients were screened for elements usually associated with increased microarousals—such as periodic limb movements or sleep apneas–hypopneas—and only the CFS patients without those conditions were included in the study. So this higher level of MAI is not yet associated with any known factor or variable except group diagnosis.

Overall, however, analysis of the findings shows CFS patients to be the most tired, and SAHS, the most sleepy. These data confirm the subjective clinical picture and support the theoretical distinction between fatigue and sleepiness. However, these distinctions are not clear-cut, especially for sleepiness, and the findings also confirm the likely overlap in the perception and operationalization of sleepiness and fatigue.

This study and its findings suggest that complaints of fatigue and sleepiness can overlap in patients, but should be taken into account separately as they may express very different etiologies and may imply different treatment considerations.

Neu D, Hoffman G, Moutrier R, Verbank P, Linkowski P, Er Le Bon O. Are patients with chronic fatigue syndrome just “tired” or also “sleepy”? Journal of Sleep Research; doi: 10.1111/j.1365-2869.2008.00679.x

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