Interactive Effects of Dementia Severity and Comorbidities on Medicare Expenditures

Background: Few studies have examined how dementia and comorbidities may interact to affect healthcare expenditures. Objective: To examine whether effects of dementia severity on Medicare expenditures differed for individuals with different levels of comorbidities. Methods: Data are drawn from the Washington Heights-Inwood Columbia Aging Project (WHICAP). Comprehensive clinical assessments of dementia severity were systematically carried out at ∼18 month intervals. Dementia severity was measured by Clinical Dementia Rating (CDR). Comorbidities were measured by a modified Elixhauser comorbidities index. Generalized linear models examined effects of dementia severity, comorbidities, and their interactions on Medicare expenditures (1999-2010). Results: At baseline, 1,280 subjects were dementia free (CDR = 0, 66.4), 490 had very mild dementia (CDR = 0.5, 25.4), 108 had mild dementia (CDR = 1, 5.6), and 49 had moderate/severe dementia (CDR = 2/3, 2.5). Average annual Medicare expenditures for individuals with moderate/severe dementia were more than twice as high as those who were dementia free (CDR = 0: $9,108, CDR = 0.5/1: $11,664, CDR≥2: $19,604, p < 0.01). Expenditures were approximately 10 times higher among those with≥3 comorbidities than among those with no comorbidities ($2,612 for those with no comorbidities, to $6,109 for those with 1, $10,656 for those with 2, and $30,244 for those with≥3 comorbidities, p < 0.001). Dementia severity was associated with higher expenditures, but comorbidities were the most important predictor of expenditures. We did not find strong interaction effects between number of comorbidities and dementia severity. Conclusions: Increasing dementia severity and higher comorbidities are associated with higher Medicare expenditures. Care of individuals with dementia should focus on management of comorbidities.