Relationships among depression, chronic pain, chronic disabling pain, and medical costs

Although evidence suggests that patients with depression use more medical services than those without depression, few studies have examined whether specific subgroups of patients with depression have higher utilization than others. The study compared costs for general medical care with and without psychiatric care for patients with major depression and disabling chronic pain (reference group) with costs for five other groups: those with depression and nondisabling chronic pain, those with major depressive disorder alone, those with no depression who had disabling chronic pain, those with depression who had chronic pain that was not disabling, and those who had neither pain nor depression. Costs for the group with major depressive disorder alone were compared to costs for the three groups without depression.

A questionnaire assessing major depressive disorder, chronic pain, and pain-related disability was mailed to a random sample of Kaiser Permanente patients who visited a primary care clinic. A total of 5,808 patients responded (54% participation rate). Costs for a two-year period were obtained from Kaiser Permanente's Cost Management Information System. Analyses were adjusted for presence of any of four major chronic medical illnesses.

Total costs for patients in the reference group were significantly higher than costs for the other five subgroups. Regression analyses indicated that continuous measures of severity of pain and severity of depression were associated with increased costs, but no statistically significant interaction of depression and pain on total cost was observed.

Patients with major depressive disorder and comorbid disabling chronic pain had higher medical service costs than other groups of patients with and without depression. However, findings suggest that the increases in cost from having both pain and depression are additive and not multiplicative.