A distinction has been noted between the cortical dementia typically seen in Alzheimer's or Pick's disease and the subcortical dementia typified by Huntington's and Parkinson's disease but noted also in progressive supranuclear palsy, multiple sclerosis, Wilson's disease, and human immunodeficiency virus (HIV) infection. y Dementia seen in diseases with primarily subcortical neuropathology feature slowed movement (bradykinesia) and thought (bradyphrenia), disproportionate problems in the efficient use of memory, poor planning, judgment, and reasoning, and often affective changes.
The distinction is not absolute because most of these diseases are not limited to either cortical or subcortical regions, and therefore many patients exhibit elements of both kinds of dementia. Most of the differences between cortical and subcortical dementia are matters of degree and proportion rather than strict dichotomies. These characteristic differences in the patterns of dementias may be more distinct in the early, mild stages; the distinctions are less clear in later stages.
When measured formally, impairments in speed of mental processing, working memory, reasoning, and strategic memory (e.g., recall) are evident in nondemented patients with striatal diseases, including patients with early Parkinson's disease. y These deficits are highly intercorrelated, suggesting that they reflect a family of interacting memory processes mediated by frontostriatal neural circuits. In nondemented patients, these deficits may be circumscribed, and the patients perform normally on tests of immediate memory, semantic memory, nonstrategic declarative memory (recognition), and language. When dementia develops in a patient with a subcortical disease, problems in speed of mental processing, working memory, reasoning, and strategic memory then become disproportionately severe relative to other problems in language or memory. The disproportionate deficit in strategic memory may be contrasted with the more proportionate and global declarative memory deficits (e.g., recall and recognition) seen in persons with Alzheimer's disease or amnesia. In addition, demented patients with Parkinson's or Huntington's disease often have deficits in procedural forms of memory, motoric and nonmotoric, that remain intact in patients with Alzheimer's disease and amnesia. Thus, disproportionate impairments in speed of mental processing, working memory, reasoning, strategic memory, and procedural memory may reflect disproportionate damage to the frontostriatal regions in diseases that initially affect those brain regions.
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