To investigate the differential nature of disturbed sleep in patients with fibromyalgia (FM) reporting sleep difficulties versus patients with primary insomnia (PI) and patients who do not report disturbed sleep (pain-free controls).
Patients (FM: n=132; PI: n=109; normals: n=52) were recruited for different studies. FM and PI patients were preselected to meet the sleep disturbance criteria. Patients with sleep or circadian disorders were excluded from all groups. Polysomnography was conducted at screening, during 2 consecutive nights. For this post hoc analysis of polysomnographies, length and frequency (duration, number) of wake and sleep bouts were analyzed, together with traditional sleep measures; a "bout"=consecutive 30-second epochs of sleep or wake. Data are mean±SD.
FM and PI patients had decreased total sleep time and slow-wave sleep (SWS), and increased latency to persistent sleep (LPS) and wake time after sleep onset (WASO) versus controls (P<0.05 for each). FM versus PI patients had more SWS (48.1±32.4 vs. 27.2±23.6 min; P<0.0001) and shorter LPS (58.2±29.8 vs. 70.7±31.3 min; P=0.0055), but comparable WASO (107.7±32.8 vs. 108.6±31.5 min). Despite comparable WASO, FM patients had shorter (4.64±2.42 vs. 5.87±3.15 min; P=0.0016) but more frequent wake bouts versus PI patients (41.6±16.7 vs. 35.7±12.6; P=0.0075). Sleep bout duration was similar for FM (9.32±0.35 min) and PI patients (10.1±0.37 min); both populations had shorter sleep bout duration versus controls (15.7±0.7 min; P<0.0001 both).
Increased frequency of wake and sleep bouts and decreased wake bout duration, together with decreased LPS and increased SWS, suggests that sleep in FM is characterized by an inability to maintain continuous sleep but a greater sleep drive compared with PI.