Cyclic alternating pattern (CAP) : a new marker of sleep alteration in patients with fibromyalgia?

Objective. In the dynamic organization of sleep, cyclic alternating pattern (CAP) expresses a condition of instability of the level of vigilance that manifests the brain's fatigue in preserving and regulating the macrostructure of sleep. We evaluated the presence of CAP in patients with fibromyalgia (FM) compared to healthy controls. Methods. Forty-five patients with FM (42 women) were studied and compared with 38 healthy subjects (36 women) matched for age, sex, and body mass index. Entry criteria were diagnosis of FM according to 1990 American College of Rheumatology criteria; willingness to participate in the study; and having no other diagnosis of autoimmune, neoplastic, or other possible causes of secondary diffuse musculoskeletal pain. Patients in the study underwent polysomnography recordings and a sleep questionnaire. Hypersomnolence was evaluated according to the Epworth Sleepiness Scale. Results. FM patients had less sleep efficiency (sleep time/time in bed) than controls (79 ± 10 vs 89 ± 6; p < 0.01), a higher proportion of stage 1 non-rapid eye movement (non-REM) sleep (20 ± 5 vs 12 ± 5; p < 0.001), and twice as many arousals per hour of sleep (9.7 ± 3.3 vs 4.1 ± 1.9; p < 0.01). The CAP rate (total CAP time/non-REM sleep time) was significantly increased in FM patients compared to controls (68 ± 6% vs 45 ± 11%; p < 0.001). CAP rate seemed to correlate with the severity of clinical symptoms in FM patients (tender points index; p < 0.01) and with less efficiency of sleep (p < 0.01). Conclusion. The increase of CAP rate indicates a worse quality of sleep in patients with FM, These data are strongly correlated to the severity of symptoms.