Chronic pain, depression, and quality of life: Correlations and predictive value of the SF-36

Objective. Depression is a major barrier to effective pain relief. The SF-36 Health Survey may be useful as an outcome measure for chronic pain patients with and without depression. The study purpose was to determine the correlation between the SF-36 Mental Composite Scale t-score and depression type in chronic pain patients and the positive predictive value of the SF-36 in classifying depression type in chronic pain patients. Design. Cross-sectional survey of chronic pain patients at baseline assessment. Setting. Interdisciplinary pain management center in the North Central United States. Patients. Two hundred forty-two consecutive, chronic noncancer pain patients. Interventions. Assessments of patient-reported health-related quality of life (SF-36), pain, pain type and diagnoses, mental health diagnoses, and patient demographics. Outcome measures. SF-36 Health Survey, pain diagnoses, and depression diagnoses. Results. Study participants were 160 women (66%) and 82 men (34%), 95% Caucasian, whose mean age was 46 (+/-0.8 SD) years (range: 19-83). All types and diagnoses of chronic pain were represented. The prevalence of major depressive disorder was 52%. The type of depression was highly correlated with SF-36 score (r=-0.567; P < 0.001). All chronic pain patients had very low SF-36 scores. Compared with U.S. population norms, chronic pain patients with and without depression had significantly lower SF-36 scores as measured by z-scores. Chronic pain patients with major depressive disorder had a significantly lower Mental Composite Score t-score than those with minor or no depression-34.1 and 47.6, respectively (P < 0.001). The positive predictive value of the SF-36 for differentiating major depression from minor or no depression was 98% (sensitivity=84.4%, specificity=93.9%). Conclusions. The SF-36 Mental Composite Score and all subscales were highly correlated with depression type in chronic pain patients. The positive predictive value of the SF-36 in classifying depression type was high. The SF-36 may be a useful clinical tool to measure health-related quality of life in chronic pain patients. In addition, the SF-36 was able to detect major depression and demonstrate a dose-effect relationship between depression type (severity) and health-related quality of life in chronic pain patients.