Individuals with primary insomnia often have poorer self-reported sleep than objectively measured sleep, a phenomenon termed negative sleep discrepancy. Recent studies suggest that this phenomenon might differ depending on comorbidities. This study examined sleep discrepancy, its night-to-night variability, and its correlates in comorbid insomnia and fibromyalgia.
Sleep diaries and actigraphy data were obtained from 223 adults with fibromyalgia and insomnia (age = 51.53 [standard deviation = 11.90] years; 93% women) for 14 days. Sleep discrepancy was calculated by subtracting diary from actigraphy estimates of sleep onset latency (SOL-D), wake after sleep onset (WASO-D), and total sleep time (TST-D) for each night. Night-to-night variability in sleep discrepancy was calculated by taking the within-individual standard deviations over 14 days. Participants completed measures of mood, pain, fatigue, sleep/pain medications, nap duration, and caffeine consumption.
Average sleep discrepancies across 14 days were small for all sleep parameters (< 10 minutes). There was no consistent positive or negative discrepancy. However, sleep discrepancy for any single night was large, with average absolute discrepancies greater than 30 minutes for all sleep parameters. Greater morning pain was associated with larger previous-night WASO-D, although diary and actigraphy estimates of WASO remained fairly concordant. Taking prescribed pain medications, primarily opioids, was associated with greater night-to-night variability in WASO-D and TST-D.
Unlike patients with primary insomnia, patients with comorbid fibromyalgia do not exhibit consistent negative sleep discrepancy; however, there are both substantial positive and negative discrepancies in all sleep parameters at the daily level. Future research is needed to investigate the clinical significance and implications of high night-to-night variability of sleep discrepancy, and the role of prescribed opioid medications in sleep perception.