The diagnosis of Alzheimer's disease: a question of image?

The most common cause of dementia in the developed world is Alzheimer's disease. Histopathology is required to confirm diagnosis, but most evaluations of the accuracy of clinical criteria and neuroimaging in the diagnosis of dementia of the Alzheimer type are without such confirmation. The average specificity of clinical criteria alone is about 75%. This paper discusses the contribution of simple structural (x-ray computed tomography [CT]) and functional (Tc-99m-HMPAO single photon emission computed tomography [SPECT]) imaging to the diagnosis of Alzheimer's disease in 71 histopathologically confirmed cases (47 with Alzheimer's disease, 16 with other dementias, 8 controls) and 84 living controls. Medial temporal lobe atrophy assessed by temporal lobe-oriented CT gave 94% sensitivity and 93% specificity, while parietotemporal hypoperfusion on SPECT revealed 96% sensitivity and 89% specificity. The combination of both changes yielded a sensitivity of 90% and a specificity of 97%. These investigations clearly enhance diagnostic accuracy, can be readily applied in the clinical situation, and could be used in epidemiologic studies of Alzheimer's disease.