Does a positive Pittsburgh Compound B scan in a patient with dementia equal Alzheimer disease?

The clinical role of amyloid brain positron emission tomographic imaging in the diagnosis of Alzheimer disease is currently being formulated. The specificity of a positive amyloid scan is a matter of contention.

An 83-year-old Canadian man presented with a 5-year history of predominantly short-term memory loss and functional impairment. Clinical evaluation revealed significant, gradually progressive short-term memory loss in the absence of any history of strokes or other neuropsychiatric symptoms. The patient met clinical criteria for probable Alzheimer disease but had a higher than expected burden of white matter disease on magnetic resonance imaging. A positron emission tomographic Pittsburgh Compound B scan was highly positive in typical Alzheimer disease distribution. The patient died of an intracerebral hemorrhage 6 months after the assessment. Autopsy revealed cerebral amyloid angiopathy in the complete absence of amyloid plaques or neurofibrillary tangles.

This patient demonstrates that a positive Pittsburgh Compound B scan in a patient with clinical dementia meeting criteria for probable Alzheimer disease is not proof of an Alzheimer disease pathophysiological process. A positive Pittsburgh Compound B scan in typical Alzheimer disease distribution in a patient with dementia can be secondary to cerebral amyloid angiopathy alone.