Error behaviors associated with loss of competency in Alzheimer's disease

Objective: To investigate qualitative behavioral changes associated with de clining medical decision-making capacity (competency) in patients with AD. Background: Qualitative measures can yield clinical information about funct ional changes in neurologic disease not available through quantitative meas ures. Methods: Normal older controls (n = 21) and patients with mild and mo derate probable AD (n = 72) were compared using a standardized competency m easure and neuropsychological measures. A system of 16 qualitative error sc ores representing conceptual domains of language, executive dysfunction, af fective dysfunction, and compensatory responses was used to analyze errors produced on the competency measure. Patterns of errors were examined across groups. Relationships between error behaviors and competency performance w ere determined, and neurocognitive correlates of specific error behaviors w ere identified. Results: AD patients demonstrated more miscomprehension, fa ctual confusion, intrusions, incoherent responses, nonresponsive answers, l oss of task, and delegation than controls. Errors in the executive domain ( loss of task, nonresponsive answer, and loss of detachment) were key predic tors of declining competency performance by AD patients. Neuropsychological analyses in the AD group generally confirmed the conceptual domain assignm ents of the qualitative scores. Conclusions: Loss of task, nonresponsive an swers, and loss of detachment were key behavioral changes associated with d eclining competency of AD patients and with neurocognitive measures of exec utive dysfunction. These findings support the growing linkage between execu tive dysfunction and competency loss.