PET, SPECT findings challenge office test results for Alzheimer’s disease

How well a patient can count, remember word lists, or perform other basic tests may not indicate how far Alzheimer's dementia has progressed biologically, researchers said Wednesday afternoon.

The Mini-Mental Status Exam has been the standard diagnostic tool for Alzheimer's disease for years, relying on a series of simple cognitive tests to calculate a score for degree of mental impairment. In 58 patients who also underwent PET or SPECT imaging, however, the MMSE showed little correlation with imaging evidence of advanced disease.

Many patients with near-normal MMSE scores showed pronounced bilateral defects on imaging, while others with extremely low MMSE scores showed only moderate PET or SPECT perfusion defects, according to Amitha Rao, a third-year medical student at the University of Kansas, who completed the research under the direction of radiologist Dr. Reginald Dusing.

Patients were excluded from the study if they showed evidence of non-Alzheimer's dementias, vascular defects, or other conditions that could mimic symptoms or invalidate imaging findings. Two readers, board-certified in both radiology and nuclear medicine, interpreted the studies.

The lack of correlation between the two types of tests adds muscle to the theory that adding PET or SPECT may speed the diagnosis of Alzheimer's, Rao said.

PET has secured limited Medicare reimbursement as an imaging agent in dementia cases, but only to rule out non-Alzheimer's dementias that can not be distinguished clinically from Alzheimer's.