Of all the movement disorders, Huntington's disease has been most consistently associated with dementia, while it is only over the last decade that intellectual and cognitive decline have been recognized as common features of Parkinson's disease. It is now known that the pathology in these two conditions reflects differential involvement of the striatum. The Huntington lesion is primarily in the caudate, while the Parkinson lesion preferentially affects the putamen. Both conditions have more diffuse pathology, and dementia may also occur in a wide range of other extrapyramidal diseases, such as progressive supranuclear palsy, the parkinsonism-dementia complex of Guam, and certain spinocerebellar degenerations. Clinicopathological correlations will be reviewed in these disorders of primarily subcortical pathology, and comparisons will be made with Alzheimer's disease, a disorder of predominantly cortical pathology.

The clinical course of vascular dementia has been described as a stepwise deterioration over time. We studied the chronologic course of cognitive performance over 1-4 years in seven patients with known ischemic cerebrovascular disease whose dementia subtype was assigned according to the clinical history and the pattern of white matter lesions seen on magnetic resonance imaging (MRI). One patient had the lacunar state, three had subcortical arteriosclerotic encephalopathy and three had multiple cortical and subcortical strokes. All were being treated with an antiplatelet agent and six received antihypertensive therapy. Four of the seven vascular dementia patients improved cognitively over the first year. A fluctuating course was eventually seen in all patients. None showed stepwise deterioration of cognitive function over time. The MRI was useful in subclassifying vascular dementia patients, but the clinical course did not appear to vary as a function of the dementia subtype.

100% of brains of Down's adults over age 40 will show Alzheimer-type neuropathologic changes in the frontal and temporal lobes. In an attempt to image these lesions, magnetic resonance imaging (MRI) was performed in seven patients with Down's syndrome, ranging in age from 17 to 45 years, using a resistive unit operating at 0.15 Tesla. All scans were within normal limits except for one 45 year-old patient with severe left temporal lobe atrophy. No areas of abnormal signal were seen in the frontal or temporal lobes and the white matter lesions commonly seen in elderly demented subjects were not visualized in this group. We conclude that these white matter lesions are likely coincidental and not causally related to Alzheimer's changes. The pathologic process leading to the formation and development of Alzheimer's changes in the brains of Down's adults may not be visible on magnetic resonance images.

Dementia of the Alzheimer type (DAT) has proven to be difficult to diagnose using computerized X-ray tomography (CT). To improve the identification of DAT with CT, several different quantitative approaches have been tried. Brain parenchymal density measurements and a variety of linear indices of ventricular size have failed to reliably separate DAT patients from age matched controls. Measures of ventricular volume improve discrimination, but overlap with controls persists. The inadequacy of a single CT study to diagnose DAT is clearly related to the overlap of brain atrophy in DAT and healthy aging, a finding which has also been noted in post-mortem studies. Estimating the rate of ventricular enlargement from quantitative measurements of ventricular size on successive CT scans may allow the physician to take advantage of the progressive nature of DAT, improving separation of DAT patients from healthy controls.