The relationship between chronic pain and depression is controversial and the data on association show strong variation. This study aimed to provide refined correlation and regression data on the basis of categorical and continuous measures.
Cross-sectional assessment was based on standardized instruments that measure on a quasi-continuous scale, the Short Form-36, the Hospital Anxiety and Depression Scale, and the Multidimensional Pain Inventory. Correlations between depression and pain were determined by the instruments' scales, with and without correction for confounders, and within chronic pain subgroups using multivariate regression analysis.
In 273 chronic pain patients participating in an inpatient pain rehabilitation program, the Multidimensional Pain Inventory pain severity scale and the Hospital Anxiety and Depression Scale showed maximum overall correlations of 0.27 to 0.29 (bivariate) and 0.30 (partial). The odds ratios for depression varied between 1.72 and 2.10 for different pain levels. Distinguishing 3 subtypes of pain patients, the pain-depression correlation was moderate in the “interpersonally distressed” subgroup (up to 0.57) (characterized by relatively low support, high punishing, low solicitous, and low distracting responses), weak in the “dysfunctional” subgroup (up to 0.26), and absent in the “adaptive copers/minimizers” subgroup (up to −0.09).
The strengths of the pain-depression association and the “dose-response” relationship were both weak—weaker than to be expected if the hypothesis of a causal relationship were true. In the interpersonally distressed subgroup, the moderate association may have an impact on pain management, that is, pain could be treated by treatment of depression and vice versa.