Implications of comorbidity on costs for patients with Alzheimer disease

Background: No prior studies have used a comprehensive clinical classification system to examine the effect of differences in overall illness burden and the presence of other diseases on costs for patients with Alzheimer disease (AD) when compared with demographically matched nondemented controls. Study Design: Of a total of 627,775 enrollees who were eligible for medical and pharmacy benefits for 2003 and 2004 in the MarketScan Medicare Supplemental and Coordination of Benefits Database, we found 25,109 AD patients. For each case, 3 demographically matched nondemented controls were selected using propensity scores. Applying the diagnostic cost groups (DCGs) model to all enrollees, 2003 diagnoses were used to estimate prospective relative risk scores (RRSs) that predict 2004 costs from all illness other than AD. RRSs were then used to control for illness burden to estimate AD's independent effect on costs. Results: Compared with the control group, the AD cohort has more comorbid conditions (8.1 vs. 6.5) and higher illness burden (1.23 vs. 1.04). Individuals with AD are more likely to have mental health conditions, neurologic conditions, cognitive disorders, cerebrovascular disease, diabetes with acute complications, and injuries. Annual costs for AD patients are $3567 (34%) higher than for controls. Excess costs attributable to AD, after controlling for non-AD illness burden, are estimated at $2307 per year with outpatient pharmacy being the key driver ($1711 in excess costs). Conclusions: AD patients are sicker and more expensive than demographically matched controls. Even after adjusting for differences in illness burden, costs remain higher for AD patients.