Contribution of neuroimaging in the diagnosis of Alzheimer's disease and other dementias.

This paper reviews the use of neuroimaging in the diagnosis of dementia, especially Alzheimer's disease. Computed tomography is still used to determine reversible causes of dementia; however, without clinical symptoms these causes are hard to find and computed tomography scanning is only cost-effective in a defined group of patients. Using magnetic resonance imaging, atrophy of the medial temporal lobe can be assessed volumetrically and visually, with a high correlation between the two methods. Medial temporal lobe atrophy is highly predictive of Alzheimer's disease, and correlates with neuropsychological performance and postmortem histologically measured volume. Cerebral volume changes over time seem to differentiate Alzheimer's disease and mild cognitive impairment progressing to Alzheimer's disease from controls with high accuracy. Studies of the corpus callosum in dementia indicate a cortico-cortical disconnection caused by atrophy. Of the new techniques, functional magnetic resonance imaging seems the most promising. This technique can possibly play a role in predicting Alzheimer's disease in patients with mild cognitive impairment. The use of single-photon emission computed tomography and positron emission tomography in (early) differential diagnoses seems limited. Lower regional cerebral blood flow is related to the severity of dementia and survival. Iodine-123 iodobenzamide single-photon emission computed tomography in dementia with Lewy bodies seems promising. Current and future positron emission tomography studies concentrate on memory function and receptor imaging. The focus in neuroimaging, especially magnetic resonance imaging, has shifted to early diagnosis and monitoring of the disease course, with a special interest in predicting dementia in patients with mild cognitive impairment.