Sleep disturbances are highly prevalent in patients with chronic pain. However, the majority of studies to date examining sleep disturbances in patients with chronic pain have been population-based cross-sectional studies. The aims of this study were to 1) examine the frequency of sleep disturbances in patients referred to two interdisciplinary chronic pain clinics in Denmark, 2) explore associations between sleep disturbances and pain intensity, disability and quality of life at baseline and follow-up, and 3) explore whether changes in sleep quality mediated the relationships between pain outcomes at baseline and pain outcomes at follow-up.
We carried out a longitudinal observational study, examining patients enrolled in two chronic pain clinics assessed at baseline (n=2,531) and post-treatment follow-up (n=657). Patients reported on their sleep disturbances using the sleep quality subscale of the Karolinska Sleep Questionnaire (KSQ), their pain intensity using 0-10 numerical rating scales, their pain-related disability using the Pain Disability Index (PDI), and quality of life using the EuroQol-VAS scale. The average time between baseline and follow-up was 207 days (SD=154).
At baseline, the majority of patients reported frequent sleep disturbances. We found a significant association at baseline between self-reported sleep disturbances and pain intensity, pain-related disability, and quality of life, where greater sleep disturbance was associated with poorer outcomes. At follow-up, patients reported significant improvements across all pain and sleep outcomes. In two mediation models, we showed that changes in sleep disturbances from baseline to follow-up were significantly associated with (i) pain intensity at follow-up, and (ii) pain disability at follow-up. However, baseline pain intensity and disability scores were not associated with changes in sleep disturbances and, we did not find evidence for significant mediation of either pain outcome by changes in sleep disturbances.
Self-reported sleep disturbances were associated with pain outcomes at baseline and follow-up, with greater sleep disturbances associated with poorer pain outcomes. Changes in sleep quality did not mediate the relationships between baseline and follow-up scores for pain intensity and disability. These findings contribute to a growing body of evidence confirming an association between sleep and chronic pain experience, particularly suggestive of a sleep to pain link. Our data following patients after interdisciplinary treatment suggests that improved sleep is a marker for a better outcome after treatment.

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