Cognitive deficits in non-Alzheimer's degenerative diseases.

Although observed in various brain disorders, dementia is particularly frequent in neurodegenerative diseases. Alzheimer's disease is characterized by the association of progressive amnesia with either instrumental (aphasia, apraxia, agnosia) or behavioral (apathy, indifference, anosognosia) disorders, depending upon the location of the underlying neuronal lesions. By contrast, memory, linguistic, praxic, visuo-spatial or comportemental impairments are dissociated in more focal "lobar" atrophies, while planning and retrieval deficits predominate in movement disorders with dementia. Alzheimer's and non-Alzheimer's neurodegenerative diseases can therefore be distinguished insofar as the severity and location of the associated neuronal lesions differ. Dementia may be observed in various brain diseases, either vascular, metabolic, demyelinating, traumatic, infectious, inflammatory, neoplastic or hydrocephalus (Chui, 1989). It is particularly frequent in neurodegenerative diseases. The recent clinical description of focal lobar atrophies (Weintraub and Mesulam, 1993) and the analysis of cognitive impairment observed in diseases with movement disorders (Cummings and Benson, 1984) have changed the conception of dementia, that may no more be defined as a global deterioration of higher cortical functions. The relative specificity of the cognitive picture of each disease depends on the location of the underlying neuronal lesions. Together with other tools, such as the neurological examination or the functional imagery, the neuropsychological exam may contribute to characterize the clinical picture of a patient with non-Alzheimer's degenerative disease and therefore to determine a clinical diagnosis, that remains probable till the neuropathological confrontation.