TOWARD A NEUROLOGIC MODEL OF COMPETENCE - COGNITIVE PREDICTORS OF CAPACITY TO CONSENT IN ALZHEIMERS-DISEASE USING 3 DIFFERENT LEGAL STANDARDS

Objective: To identify cognitive predictors of competency performance and status in Alzheimer's disease (AD) using three differentially stri ngent legal standards for capacity to consent. Design: Univariate and multivariate analyses of independent neuropsychological test measures with three dependent measures of competency to consent to treatment. S etting: University medical center. Subjects: 15 normal older controls and 29 patients with probable AD (15 mild and 14 moderate). Main Outco me Measures: Subjects were administered a battery of neuropsychologica l measures theoretically linked to competency function, as well as two clinical vignettes testing capacity to consent to medical treatment u nder five legal standards (LSs). The present study focused on three di fferentially stringent LSs: the capacity simply to ''evidence a treatm ent of choice'' (LS1), which is a minimal standard; the capacity to '' appreciate the consequences'' of a treatment choice (LS3), a moderatel y stringent standard; and the capacity to ''understand the treatment s ituation and choices'' (LS5), the most stringent standard. Control sub ject and AD patient neuropsychological test scores were correlated wit h scores on the three LSs. The resulting univariate correlates were th en analyzed using stepwise regression and discriminant function to ide ntify key multivariate predictors of competency performance and status under each LS. Results: No neuropsychological measures predicted cont rol group performance on the LSs. For the AD group, a measure of simpl e auditory comprehension predicted LS1 performance (r(2) = 0.44, p < 0 .0001), a word fluency measure predicted LS3 performance (r(2) = 0.58, p < 0.0001), and measures of conceptualization and confrontation nami ng together predicted LS5 performance (r(2) = 0.81, p < 0.0001). Under discriminant function analysis, confrontation naming was the best sin gle predictor of LS1 competency status for all subjects, correctly cla ssifying 96% of cases (42/44). Measures of visuomotor tracking and con frontation naming were the best single predictors, respectively, of co mpetency status under LS3 (91% [39/43]) and LS5 (98% [43/44]). Conclus ions: Multiple cognitive functions are associated with loss of compete ncy in AD. Deficits in conceptualization, semantic memory, and probabl y verbal recall are associated with the declining capacity of mild AD patients to understand a treatment situation and choices (LS5); execut ive dysfunction with the declining capacity of mild to moderate AD pat ients to identify the consequences of a treatment choice (LS3); and re ceptive aphasia and severe dysnomia with the declining capacity of adv anced AD patients to evidence a simple treatment choice (LS1). The res ults offer insight into the relationship between different legal thres holds of competency and the progressive cognitive changes characterist ic of AD, and represent an initial step toward a neurologic model of c ompetency.