Impaired physical performance and the assessment of dementia of the Alzheimer type

Context: Impaired physical performance may confound the clinical assessment of dementia of the Alzheimer type (DAT). Objectives: Determine whether: (1) Physical Performance Test (PPT) scores are associated with the Clinical Dementia Rating (CDR), (2) PPT scores are correlated with clinical measures of health, and (3) impaired physical performance affects the clinical assessment of DAT. Design: A retrospective and cross-sectional study. Setting: An Alzheimer's Disease Research Center. Participants: Ninety-nine research volunteers aged 85 years and older were assessed from September 1997 through July 1999; 45 had DAT (CDR=0.5-2), and 54 were nondemented controls. Measurements: Clinical health history, daily functioning, physical and neurologic status, CDR, sum of boxes, and total PPT score were obtained during clinical evaluation. Independently assessed psychometric measures of verbal and nonverbal episodic and semantic memory, visuospatial abilities, and psychometric speed yielded to a factor score representing general cognitive function. Our outcome measure was the CDR (ie, the clinical dementia rating, where higher scores indicate greater dementia severity). Results: The majority (88%) of subjects in this sample of demented and nondemented older adults had some degree of physical impairment as measured by the PPT. Correlational analyses identified clinically important relationships (\tau(b)\greater than or equal to0.30, p<0.05) between impaired PPT performance, higher CDR rating, and poor general health, including difficulty ambulating. The correlation between PPT performance and dementia severity (tau(b)=-0.36) decreased after controlling for cognitive ability (tau(b)=-0.19). The correlation between the cognitive factor score and dementia severity when PPT performance was controlled (tau(b)=-0.60) was similar to the unadjusted correlation of the factor score with dementia severity (tau(b)=0.64). Conclusions: The presence of some degree of physical impairment was common in our sample, and PPT scores correlated with both physical and cognitive impairment. Nevertheless, Alzheimer Disease Research Center clinicians appear able to successfully distinguish between physical and cognitive causes of functional impairment and assign a CDR rating that accurately reflects DAT severity in individuals with impaired physical performance.