The association of depression with pain-related treatment utilization in patients with multiple sclerosis

A common secondary condition experienced by persons with multiple sclerosis (MS) is chronic pain (1), which is prevalent in 50–65% of community samples with MS, approximately one fourth of whom describe their pain as severe (2–4). For many persons with MS, the treatment of chronic pain can contribute to high rates of medical service utilization and subsequent higher health care costs relative to healthy controls (5). For example, one recent community-based survey of adults with MS (Ehde et al., under review) found that participants with chronic pain reported utilizing nine pain treatments on average, and sought health care for pain from a variety of sources in the previous six months, including primary care providers (62%), specialists (47%), and emergency departments (11%). Not surprisingly, in a study of Australians with MS, participants with pain reported greater utilization of medical services for pain than those without pain, with nonopiod analgesics and “physical measures” [defined as “change in position, massage, change of clothes, comfortable furniture, pressure, whirlpool, transcutaneous electrical nerve stimulation (TENS), electric vibrator”] as the most commonly used treatments for pain (4). Any of a number of variables may contribute to between-patient differences in pain treatment utilization. A likely factor is depression, which is commonly experienced by persons with MS and often co-occurs with pain. The lifetime prevalence of major depressive disorder is 50% in individuals with MS, the point-prevalence is 15–25%, and clinically significant levels of depression approach 50% at any one time (6–9). In the only known study to clearly define this comorbidity, 53.2% of people with MS and pain were above the clinical cutoff on a measure of depression (based on CES-D score), whereas 32.9% of those with MS who did not report pain scored above the clinical cutoff, a statistically significant difference (10). Moreover, greater depressive symptomatology is associated with worse pain in persons with MS (11). In non-MS populations, depression is associated with higher medical services utilization and costs when all healthcare treatment is considered. Depression is associated with more medical visits among primary care patients (12), back pain patients (13), and persons following stroke (14), and more medical costs among patients selected from an insurance provider (15, 16). Depression is also associated with both more medical visits and higher medical costs among youth with asthma (17) and the general public (18). Specific types of visits are more common among those who are depressed, including primary care, mental health, and emergency room (17); it is often stated that 60–70% of primary care visits are due to psychological distress, including depression, that is displayed through physical symptoms (19). However, among back pain patients, back pain-specific visits were not higher among depressed persons after controlling for symptom severity (20) and, similarly, among youth with asthma, total medical utilization was higher but asthma-specific visits were not higher among depressed persons (17). The mechanism by which depression impacts treatment utilization is less clear. For example, some have reported that depressed patients often seek treatment for somatic symptoms that could be attributed to depression (21), suggesting that this excess utilization would be reduced by effective depression treatment (22). Alternatively, in the context of pain, depression is associated with greater pain-related suffering, which could subsequently motivate an individual to seek treatment to reduce this greater level of suffering. Lastly, persons with chronic pain and depressive dispositions (e.g., greater depressive symptomatology or lower optimism) experience less relief from treatments for their pain (23, 24) and slower recovery (25), which could result in attempting more treatments before identifying a satisfactory solution. The findings summarized regarding pain, depression, and health care utilization suggest that individuals with MS who have chronic pain and depression might be more likely to seek and obtain pain treatment than those who have chronic pain but are not depressed. If this were true, it suggests that pain-related health care costs might be lowered if depression were adequately assessed and treated in this population. However, we are unaware of any studies that have explored the moderating influence of depression on pain treatment utilization among persons with MS. The primary goal of this study was to test the direct and moderating role that depression has on pain treatment in a community sample of persons with MS and chronic pain, as measured by the number of types of pain treatments currently and previously used, as well as number of visits to medical providers for pain treatment. The specific hypotheses were that: (1) individuals with depression would report more current and previous pain-related medical services utilization and (2) depression would moderate the relationship between pain intensity and pain-related medical services utilization. We did not have any a priori hypotheses about the associations between depression and specific types of pain-related medical services, as this issue has not yet been addressed in any previous study.