SLEEP-WAKE BEHAVIOR IN CHRONIC FATIGUE SYNDROME Sleep-Wake Behavior in Chronic Fatigue Syndrome

671 Sleep-Wake Behavior in CFS—Rahman et al about the mechanisms responsible for the experience of poor quality sleep in CFS. Human sleep is part of an oscillating sleep-wake pattern following a circadian rhythm.8 These cyclical rhythms are directed by the brain’s biological “clock” located in the suprachiasmatic nucleus and cause fluctuation of body temperature, hormone levels, and sleep over a 24-h period. These behavioral and physiological rhythms are synchronized to external physical environmental and social/work schedules. The strongest synchronizing agent in humans is changes in light and darkness which “set” the biological clock and help determine the need to wake up or go to sleep. The circadian clock not only provides temporal synchronization between these various rhythms, but it also promotes wakefulness, and coordinates the timing of sleep-wake behavior, which are involved in aspects of physiological and neurocognitive functioning.8 Recent evidence has underscored the importance of circadian rhythms in maintaining good health with alterations in the normal circadian clock linked to a number of conditions including mood disorders.9 Asynchrony between the internal clock and sleep-wake behavior also frequently accompanies shift work, or international travel (i.e., jet lag), leading to symptoms of fatigue, poor concentration, and sleep abnormalities.10,11 The similarity between these symptoms and those associated with CFS has stimulated research interest in disturbances in the endogenous circadian rhythm as a pathophysiological mechanism in CFS.12,13 To date, a limited number of studies assessing specific parameters of circadian rhythmicity such as sleep/wake times, activity cycles,14 melatonin excretion patterns,15 and core body temperature16 have been largely inconclusive in their outINTRODUCTION Chronic fatigue syndrome (CFS) is a severe, disabling disorder that poses a significant personal and economic burden for sufferers, their families, and the community. The etiology and pathophysiology of this enigmatic clinical disorder remains obscure, and curative therapies are not available. CFS is diagnosed by consensus-derived, criterion-based case definitions, requiring persistent, medically unexplained, fatigue for ≥ 6 months in the presence of characteristic constitutional and neuropsychiatric symptoms.1 The profound experience of unrefreshing sleep and complaints of disturbed or restless sleep are prominent in subjective reports of symptoms in CFS.2,3 While classical sleep studies employing polysomnographic techniques have shown varied, nonspecific changes in sleep structure and efficiency in a subgroup of patients with CFS, these studies have not revealed any substantive evidence indicative of a primary sleep disorder.4,5 Pertinent to this, studies of monozygotic twins discordant for CFS6,7 have not revealed any significant alterations in sleep architecture. Nevertheless, patients with CFS consistently report a profound reduction in sleep quality.4,6,7 To date, little is known SLEEP-WAKE BEHAVIOR IN CHRONIC FATIGUE SYNDROME