Sleep cycles and alpha-delta sleep in fibromyalgia syndrome

Fibromyalgia syndrome (FMS) is a musculoskeletal disorder characterized by generalized pain, localized tender points, chronic fatigue and nonrestorative sleep. Since sleep disturbances frequently occur in FMS and alpha intrusion in nonrapid eye movement (NREM) sleep probably associates with the nonrefreshing sleep, we prospectively studied the delta and alpha activity and alpha-delta ratio across sleep cycles, performing polysomnography in 10 patients with FMS and in 14 healthy control subjects.

Night long polysomnography recordings were performed in all subjects. Sleep scoring was done visually according to Rechtschaffen and Kales criteria. By means of spectral analysis the conventional electroencephalogram (EEG) frequency bands were automatically computed for the all night recordings. For alpha and delta power the integrated and normalized values were calculated for each sleep cycle, the evolution of these activities across successive sleep cycles was studied.

Alpha-delta patterns occurred in almost all the patients who had also superficial and fragmented sleep with increased awakenings and reduced REM and slow wave sleep. Delta decay across sleep cycles was different in FMS and alpha activity was greater and declined, whereas the controls were persistently low throughout their sleep. Alpha-delta ratio increased progressively in successive sleep cycles; this was again different from controls.

Patients with FMS presented a high frequency of subjective sleep disturbances, an increased incidence of alpha EEG NREM sleep and clear abnormalities in sleep cycle organization.