Executive control function: A rational basis for the diagnosis of vascular dementia
Problems with diagnostic criteria for vascular dementia (VaD) stem from the inadequacy of the current dementia concept, a paradigm based on amnestic and other cortical deficits typical of Alzheimer disease (AD). However, most cases of VaD are due to subcortical lesions such as Binswanger-type periventricular white matter ischemia, or strokes causing decreased frontal activation and diaschisis-mediated cerebral hypoperfusion. We propose a new definition of dementia based on executive dysfunction and a formal assessment of executive control functions (ECF) for the diagnosis of VaD. The instruments proposed are the rapid screening executive clock-drawing task (CLOX; Royall et al. J Neurol Neurosurg Psychiatry 1998;64:588-94), and the more comprehensive Executive Interview Test (EXIT25; Royall et al. J Am Geriatr Soc 1992;40:122-6). Extensive application of these tests in elderly subjects in retirement communities has shown that both are brief, simple to administer, and more sensitive case-finding tools for cognitively impaired individuals than the Mini-Mental State Examination (MMSE). These three tests (CLOX, EXIT25, MMSE) accurately separate nondemented subjects from those with cortical or subcortical (frontal system) dementias. In addition, for controlled clinical trials of VaD, formal evaluation of motor and frontal sphincter functions--usually not considered part of the dementia syndrome--should also be included. Evaluation of gait and falls, timed-walk, manual dexterity, timed finger-tapping, and frontal bladder control (urge incontinence and nocturia) should improve determination of functional status and disability, and more accurately measure the effects of potential therapies.