Fibromyalgia syndrome is a chronic disorder characterized by widespread musculoskeletal pain of unknown etiology and associated with a set of diverse symptoms, including sleep disturbance. In fibromyalgia there is a consistent and replicable relationship between pain and sleep disruption, with a typical pattern of night hypervigilance, superficial and unrefreshing sleep, as well as difficulty in maintaining sleep. Patients often report symptoms of stiffness, fatigue and cognitive changes in learning and memory.
Sleep disturbance in fibromyalgia can mediate, while being mediated by, a complex psychological process focused on somatic complaints, allodynia, hyperalgesia and increased persistence of pain with broad topography of referred pain. Polysomnography studies show sleep microarchitecture changes with alpha waves instrusion in NREM sleep, without a real awakening (alpha sleep), delayed sleep onset, shortening of stages 3 and 4 of NREM sleep, more frequent awakenings and stage 1 NREM sleep, REM sleep reduction and increased wake time after sleep onset.
Roizenblatt et al. described three distinct patterns of alpha sleep activity in fibromyalgia: phasic alpha (simultaneous with delta activity) in 50% of patients; tonic alpha (continuous throughout non-REM sleep) in 20% of patients; and low alpha activity in the remaining 30%.
New evidence suggests that sleep fragmentation prevents the central pain modulation process, which contributes to its diffuse hypersensitivity. Experimental studies have shown the induction of symptoms similar to fibromyalgia after triggering frequent arousals, and its resolution after removing the awakening stimulus. Along with sleep fragmentation, some patients also have associated involuntary periodic disturbances: periodic limb movements, restless legs syndrome, sleep apnea and cyclic alternating pattern (CAP).