The cognitive pattern of vascular dementia and its assessment

Abstract

Prevailing definitions of dementia are based on the Alzheimer disease (AD) model, which places major emphasis on memory impairment. In other dementias, such as vascular dementia (VaD), several other cognitive dysfunctions predominate over the memory disorder. The cognitive pattern changes according to the type of VaD. In multi-infarct dementia (MID), cortical lesions may cause loss of instrumental functions manifested by aphasia, amnesia, apraxia, or agnosia. Language in MID patients has shorter phrase length, restricted lexical variability, simplified syntax, and low verbal fluency; dysarthria or mechanical impairment of speech with abnormal pitch, melody, or articulation rate also occur. The latter are rare in degenerative dementias. Compared with AD, patients with MID demonstrate superior performance on verbal learning and memory, better delayed recall, and lower rates of forgetting, intrusions, and false positives. Subcortical ischemic dementia, subcortical hemorrhages, or single subcortical strategic infarcts frequently impair executive functions, attention, and speed of information processing; anterograde memory is generally less impaired than in AD patients. The two main problems of batteries used for evaluation of dementia such as those recommended by CERAD (verbal fluency test, a brief naming test such as the Modified Boston Naming Test, free recall of a word list, with immediate and delayed recall, followed by a recognition task of the same words, and line drawings of figures), as well as the Mini-Mental State Examination (MMSE), are (1) their strong emphasis on memory, temporal and spatial orientation, calculation, language, and constructional praxis, and (2) their failure to assess executive functions. Simple tests of executive function include the Trail Making Test, the Wisconsin Card Sorting Test, and the EXIT-25. A simple and effective test is the CLOX, an executive variation of the clock-drawing task. Depressive symptoms and other psychiatric disturbances are particularly common in VaD and become sources of cognitive and functional disability. Several questionnaires assess the neuropsychiatric manifestations of dementia including the Neuro-Psychiatric Inventory (NPI), the BEHAVE-AD test, the Cohen-Mansfield Scale, and the CERAD Behavioral Rating Scale for Dementia. Finally, development of dementia after a stroke may represent true VaD in patients with intact cognition before the stroke, or AD + CVD when the dementia occurs in patients that already had memory problems before the ictus. The diagnosis of VaD is a challenging clinical problem that encompasses the fields of medicine, neurology, psychiatry, and psychology.