Brain imaging with MRI, SPECT, and PET can improve diagnostic accuracy in differentiating Alzheimer Disease (AD) from potentially treatable causes of dementia such as toxic metabolic states, depression, and normal pressure hydrocephalus. When PET results are combined with clinical criteria, the false positive rate in AD can be reduced from 23% to 11%. The classic pattern of AD on PET imaging is bilateral temporoparietal and posterior cingulate cortex hypometabolism; abnormal metabolism can also be seen asymmetrically, particularl yearly in the disease. Frontal lobe involvement may also be seen in later stages. The exact cause for the decline in brain glucose metabolism in AD remains unclear. Hippocampal atrophy may be seen on conventional cross-sectional imaging.
Dementia With Lewy Bodies ( DLB) is another cause of cognitive decline. Patients with DLB usually have less hippocampal atrophy than do patients with Alzheimer disease and show decreased occipital lobe blood flow or metabolism in DLB but not in Alzheimer disease.
In frontotemporal dementia, frontal and anterior temporal metabolism is predominantly decreased compared to the other types of dementia
Wessam Bou-Assaly is an experienced Neuroradiologist who practices in Ann Arbor Michigan.