Differential impact of mental health multimorbidity on healthcare costs in diabetes

Objectives: This study assessed the prevalence and specific costs associated with discrete multimorbid mental health disease clusters in adults with diabetes mellitus (DM). Study Design: Longitudinal analysis of a retrospective cohort. Methods: We performed a 5-year longitudinal analysis of a retrospective cohort of 733,071 patients with DM from the US Veterans Health Administration (VHA) between 2002 and 2006. The mental health comorbidities (MHCs) examined included depression, substance abuse, and psychosis. Our primary outcomes of interest were total inpatient, outpatient, and pharmacy costs measured in 2012 US$ from the perspective of the VHA. Results: DM was present with comorbid depression, substance abuse, and psychosis in 12.1%, 3.7%, and 4.2% of patients, respectively. Overall, 13.5% of patients had 1 MHC, 2.5% had 2 MHCs, and 0.5% had all MHCs. Total inpatient ($1,435,651,415), outpatient ($366,137,435), and pharmacy ($90,064,725) costs were highest for patients with DM and comorbid depression alone. At the per-patient level, DM plus psychosis and substance abuse had the highest inpatient costs ($35,518), DM plus all MHCs had the highest outpatient costs ($6962), and DM plus depression and psychosis had the highest pharmacy costs ($1753). Conclusions: DM with comorbid depression is the most prevalent MHC combination and is associated with the highest total VHA healthcare costs. However, other comorbidity clusters are associated with higher mean per patient costs, and may therefore benefit from more intensive intervention. Analysis of healthcare expenditures by multimorbid disease clusters can be a useful tool for healthcare policy planning.