Cognitive impairment and mortality in older primary care patients

Abstract

Objective: To assess the impact of cognitive impairment on mortality in older primary care patients after controlling for confounding effects of demographic and comorbid chronic conditions.

Design: Prospective cohort study.

Setting: Academic primary care group practice.

Participants: Three thousand nine hundred and fifty-seven patients age 60 and older who completed the Short Portable Mental Status Questionnaire (SPMSQ) during routine office visits.

Measurements: Cognitive impairment measured at baseline using the SPMSQ, demographics, problem drinking, history of smoking, clinical data (including weight, cholesterol level, and serum albumin), and comorbid chronic conditions collected at baseline; survival time measured during the 5 to 7 years after baseline.

Results: Eight hundred and eighty-six patients (22.4%) died during the 5 to 7 years of follow-up. Cognitive impairment was categorized as having no impairment (84.3%), mild impairment (10.5%), and moderate-to-severe impairment (5.2%) based on SPMSQ score. Chi-square tests revealed that patients with moderate-to-severe impairment were significantly more likely to die compared with patients with mild impairment (40.8% vs 21.5%) and those with no impairment (40.8% vs 21.4%). No significant difference in crude mortality was found between patients with no impairment and those with mild impairment. After analyzing time to death using the Kaplan-Meier method, patients with moderate-to-severe cognitive impairment were at increased risk of death compared with those with no or mild impairment (Log-rank chi(2) = 55.5; P <.0001). Even in multivariable analyses using Cox proportional hazards to control for confounding factors, compared with those with no impairment, moderately-to-severely impaired patients had an increased risk of death, with a hazard ratio (HR) of 1.70. Increased risk of death was also associated with older age (HR = 1.03 for each year), a history of smoking (HR = 1.48), having a serum albumin level <3.5 g/L (HR = 1.29), and weighing less than 90% of the ideal body weight (HR = 1.98). Outpatient diagnoses associated with increased mortality risk were diabetes mellitus, coronary artery disease, congestive heart failure, cerebrovascular disease, cancer, anemia, and chronic obstructive pulmonary disease (HR range 1.36-1.67). Factors protective of mortality risk included female gender (HR = 0.67) and black race (HR = 0.73).

Conclusions: Moderate-to-severe cognitive impairment is associated with an increased risk of mortality, even after controlling for confounding effects of demographic and clinical characteristics. Mild cognitive impairment is not associated with mortality risk, but a longer follow-up period may be necessary to identify this risk if it exists.