Insomnia is a risk factor for spreading of chronic pain: A Swedish longitudinal population study (SwePain)

Background Recent evidence suggests that insomnia negatively influences the occurrence of generalized pain. This study examined whether insomnia is a risk factor for the transition from local pain (LP) to generalized pain (i.e. spreading of pain). Methods This longitudinal study, with a follow-up of 24 months, included 959 participants (mean age: 55.8 years;SD: 13.9) with local or regional pain at baseline. Participants were grouped by insomnia symptoms as measured by the Insomnia Severity Index. Spreading of pain was measured by body manikins based on the spatial distribution of pain on the body. We defined two outcome categories; one with relatively localized pain (i.e. LP and moderate regional pain [MRP]), and one with relatively generalized pain (i.e. substantial regional pain and widespread pain [WSP]). Baseline age, sex, education, depressive symptoms, anxiety symptoms, catastrophizing, pain intensity and spread of pain were also included in the Generalized Linear Model analysis. Results The unadjusted model showed that the risk of spreading of pain increased with an increase in insomnia symptoms (no insomnia: 55.4%; subthreshold insomnia: 25.4% moderate insomnia: 16.5% and severe insomnia: 2.7%). The risk increased in a dose-dependent manner; moderate insomnia risk ratio (RR) 2.34 (95% confidence interval [CI]: 1.34-4.09) and severe insomnia RR 4.13 (95% CI: 1.56-10.92). The results were maintained in the fully adjusted model although MRP was the strongest predictor RR 6.95 (95% CI: 3.11-15.54). Conclusion Our findings show a strong prospective relationship between insomnia symptoms and the transition from relatively localized to generalized pain. Significance This study shows that people with LP conditions are at much higher risk of developing WSP if they also have significant insomnia symptoms. The elevated risk is evident after 24 months and increases in a dose-dependent manner regarding the degree of exposure to insomnia symptoms. Local pain conditions are quite common in primary care, and an evaluation of the insomnia symptoms is highly recommended since the most common sleep problems can be treated effectively if detected.