Alzheimer's disease symptom severity in blacks and whites

OBJECTIVE: In order to determine whether there are racial differences in Alzheimer's Disease (AD) symptom severity and vascular comorbidities, we compared African-American (black) and Caucasian (white) patients with AD from similar socioeconomic backgrounds at the time the disease was first recognized. DESIGN: Cross-sectional observational study from a population-based dementia registry. PARTICIPANTS: Patients were enrolled from an HMO base population of 23,000 persons more than age 60 in Seattle, Washington. This study examines 453 subjects with probable AD (38 blacks (mean age 76.5, SD 6.4), and 415 whites (mean age 79.7, SD 6.7)). MEASUREMENTS: Measured were patient demographics, age at onset of AD, AD symptom duration, Mini-Mental State Exam (MMSE) score, Blessed Dementia Rating Scale, presence of psychiatric symptoms, and vascular comorbidities. RESULTS: Blacks had significantly lower mean cognitive scores (MMSE = 17.2, SD 5.6) compared with whites (MMSE = 20.2, SD 5.2, unpaired t test P < .01). The significant racial difference in MMSE scores persisted after controlling for education, duration of AD symptoms, age, and ADL impairment. Blacks and whites did not differ significantly regarding gender distribution, education level, income, or percent with early age of onset of AD. No statistically significant race-related differences were found in impairments in activities of daily living or symptoms of paranoia, hallucinations, or agitation. Blacks had significantly higher rates of hypertension (56%) compared with whites (34%) (Fisher's exact test, P = .013), but the rates of stroke and ischemic heart disease were similar. CONCLUSIONS: Despite uniform detection methods and controlling for reported duration of dementia symptoms, measured cognitive impairment is significantly more severe when AD is recognized in blacks compared with whites. The significantly higher prevalence of hypertension among black AD cases was not associated with excess cerebrovascular disease comorbidity. This study highlights a need for normative measurements of cognitive function in minority AD groups in order to distinguish differential cognitive symptom severity from possible measurement bias.