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Positron emission tomography in diagnosis of visual variant Alzheimer disease.

A 65-year-old man with a 3-year history of difficulty seeing had normal ophthalmologic and neurologic examinations except for impaired visual spatial and perceptual function. Brain MRI failed to disclose any structural abnormalities, but positron emission tomography (PET) performed 2 weeks later showed prominent hypometabolism in the parieto-occipital regions bilaterally. These findings were considered consistent with the visual variant of Alzheimer disease (VVAD). Although the dissociation between normal structural and abnormal functional imaging has been reported before in VVAD, this patient is a reminder that PET may be useful to confirm the diagnosis before the disease becomes advanced.