Cost of Depression in Japanese Patients with Rheumatoid Arthritis: Evidence from Administrative Data

Accumulating evidence from clinical and epidemiological studies indicates that depression is highly prevalent as a common comorbidity in patients affected with rheumatoid arthritis (RA) [1, 2, 3]. While the prevalence of depression differs significantly among studies, as high as 42% of patients with RA have been reported to be affected by depression [4]. Recently, a meta-analysis of 72 studies involving 13,189 individuals affected with RA found that 14.8–38.8% of such populations are often diagnosed with a major depressive disorder [5]. Furthermore, depression comorbidity of RA has been shown to be linked to a higher rate of unemployment, loss of productivity at work, as well as burden of escalating healthcare costs on both the affected individuals and society at large [6, 7, 8].

Frequently, depression comorbidity of RA remains undiagnosed and consequently under-treated [9], often due to the lack of communication about depression between the specialist and their patients [7, 10]. Previous studies have further found that individuals affected by depression comorbidity of RA are less likely to adhere to their medication regimens with subsequent elevated health care costs [7, 11]. For Japan, little is known about data on the health care utilization of depression comorbidity among RA patients. Hence, the purpose of the present study was to determine characteristics of health care utilization prevalent among the Japanese population affected with RA and comorbidity of depression.

The patient flow chart for this analysis is described in Fig. 1. From a total of 91,669 RA patients, 8968 fulfilled the inclusion criteria. Among the included patients, 474 (5%) were affected with depression as a comorbidity.

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Our findings also indicate that after matching, all observable differences between the two subpopulations (with and without depression) disappear (Table 1). The balance after matching is also evident from Fig. 2, which shows the distribution of the propensity score in the two groups before and after matching.

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The proportion of patients with hospitalization was higher in patients with depression (14 vs. 7% within 6 months; 19 vs. 9% within 12 months). Within 6 months, patients were significantly more likely to have a hospitalization [HR = 1.474 (1.053; 2.062); P = 0.024]. Within 12 months, no significant difference in the relative risk of hospitalization were found [HR = 1.064 (0.802; 1.411); P = 0.668). Average numbers of visits per month among patients with at least one hospitalization were similar [(6 months): 0.22 vs. 0.23; (12 months) 1.69 vs. 0.64].

We analyzed an administrative hospital database and found that a co-morbidity of RA and depression causes significant economic burden. The sample in our database had a similar composition as the general RA population with a majority of the patients being female and middle-aged [16].

Our database identified only 5% of patients with RA affected by depression, which is considerably lower than reported estimates of other countries [4, 5] but exceeds the respective rate of the Japanese general population [17, 18]. There are two possible explanations for this finding. The possible differences in prevalence estimates between Japan and other developed countries may be in part due to a higher reluctance for reporting of depression in the Japanese population compared to other developed countries. In Japan, individuals affected with depression were reportedly less likely to seek medical treatment or consult a psychiatrist; 27% sought any treatment with only 14% having consulted a psychiatrist. This number is considerably lower than the reported estimates from several developed countries with approximately half that of the US [17]. The other possible explanation relates to the nature of our claims database; there is a bias towards patients employed at private Japanese companies and excludes patients unable to physically perform work-related tasks due to the severity of their disease. Accordingly, the depression prevalence identified from this database may have possibly underestimated the actual prevalence rate. Our estimated prevalence of 5% is in agreement with a recent survey that similarly found only 5% of the studied population had been formally diagnosed with depression. On the other hand, 35% of the affected patients demonstrated Patient Health Questionnaire (PHQ-9) scores indicative of the presence of depression, which translates to a significant underreporting of depression in RA patients. The PHQ-9 is a versatile self-reporting tool used for measurement of depression severity, diagnosis, as well as screening for the disease [19]. The study also found that among the RA population, younger patients, those affected by greater functional impairment, or patients on pain relief medications not biologic agents were more likely to experience depression [20]. Data from the Japanese IORRA registry also indicate that up to 41% of the RA patients were identified as depressed patients using a two-question screening tool [21], while a more recent study reported prevalence rates between 6.8 and 23.5% in depending on the tool that was used to determine depression [22].

In terms of health care utilization, depression resulted in a significant increase in number of outpatient visits and emergency room admissions. However, routine hospital admissions were not higher in the populations affected by depression. Only a limited number of studies have measured health care costs or resource utilization associated with depression comorbidity of RA patients. Findings from the US database studies revealed that the annual mean healthcare costs for patients with RA and depression comorbidity were USD 12,225 compared to USD 11,404 for patients with RA alone [23]. Our results indicate that the incremental burden of depression seems to be even higher in Japan compared to the US study. Clinical implication of this study is that Japanese rheumatologists need to become acutely aware of potential depression disorders during management of RA in their patients. A multidisciplinary treatment team approach is one potentially effective solution for achieving higher awareness of depression among RA patients. A second key resolution is to involve patients in decision-making. Recently, we showed that Japanese patients affected with RA have a preference for a collaborative role in medical decision-making, especially those affected with a greater disease burden [24].

Several limitations need to be discussed in this study. First, we could not identify clinical parameters and disease severity from the claims database. This is an inherent limitation of claims database analysis in general. Therefore, identifiable factors were limited to the characteristics of patients such as age, gender, and comorbidity as well as clinical characteristics related to the treatment. Furthermore, a common problem in any database analysis is the coding quality. Most of the time, either the hospital or treating physician designates medical codes that provide the highest reimbursement rates, which is why disease codes do not always reflect clinical reality [25]. Finally, depression has a significant impact on healthcare utilization not only in RA but also other disease conditions [26].

In summary, in light of the increased burden of depression among Japanese patients with RA, treating specialists need to be more vigilant and aware of the potential for comorbidity depression impacting their patients’ quality of life and ensure that the patients are actively involved in treatment decision-making. Future large clinical studies are required to examine if the additional burden of depression is greater in patients affected with RA compared to other diseases such as cancer.