Insomnia in a chronic musculoskeletal pain with disability population is independent of pain and depression

Background context Insomnia is frequently experienced by patients suffering from chronic musculoskeletal disorders but is often seen as simply a symptom of pain or depression and not as an independent disorder. Compared with those who experience only chronic pain, patients with both chronic pain and insomnia report higher pain intensity, more depressive symptoms, and greater distress. However, insomnia has not yet been systematically studied in a chronic musculoskeletal pain with disability population. Purposes This study assessed the prevalence and severity of patient-reported insomnia, as well as the relationship among insomnia, pain intensity, and depressive symptoms, in a chronic musculoskeletal pain with disability population. Study design/setting This was a retrospective study of prospectively captured data. Patient sample A consecutive cohort of 326 chronic musculoskeletal pain with disability patients (85% with spinal injuries) entered a functional restoration treatment program. All patients signed a consent form to participate in this protocol. Outcome measures Insomnia was assessed with the Insomnia Severity Index, a validated patient-report measure of insomnia symptoms. Four patient groups were formed: no clinically significant insomnia (score, 0-7); subthreshold insomnia (score, 8-14); moderate clinical insomnia (score, 15-21); and severe clinical insomnia (score, 22-28). Three patterns of sleep disturbance were also evaluated: early, middle, and late insomnia. Additional validated psychosocial patient-reported data were collected, including the Pain Visual Analog Scale, the Beck Depression Inventory, the Oswestry Disability Index, and the Pain Disability Questionnaire. Methods Patients completed a standard psychosocial assessment battery on admission to the functional restoration program. The program included a quantitatively directed exercise process in conjunction with a multimodal disability management approach. The four insomnia groups were compared on demographic and psychosocial variables. The shared variances among insomnia, depression, and pain were determined by partial correlational analyses. Results The presence of no clinically significant insomnia, subthreshold insomnia, moderate clinical insomnia, and severe clinical insomnia was found in 5.5%, 21.2%, 39.6%, and 33.7% of the cohort, respectively. More than 70% of patients reported moderate to severe insomnia symptoms, which is a considerably higher prevalence than that found in most patient cohorts studied previously. A stepwise pattern was found, in which severe clinical insomnia patients reported the highest pain, the most severe depressive symptoms, and the greatest disability. The severe clinical insomnia patients also reported a higher number of sleep disturbance types (early, middle, and late insomnia) than the other three groups. In fact, 62.9% of them reported all three disturbance types. Although correlations were found between insomnia and depressive symptoms and between insomnia and pain, the shared variances were small (12.9% and 3.6%, respectively), indicating that depression and pain are separate constructs from insomnia. Conclusion This research indicates that insomnia is a significant and pervasive problem in a chronic musculoskeletal pain with disability population. Most importantly, although insomnia has traditionally been assumed to be simply a symptom of pain or depression, the findings of the present study reveal that it is a construct relatively independent from both pain and depression. Specific insomnia assessment and treatment is therefore recommended for this chronic musculoskeletal pain with disability population.