New EU guidelines tout FDG PET, SPECT for Alzheimers diagnosis
Updated European Federation of the Neurological Societies (EFNS) guidelines for the diagnosis and management of Alzheimer's disease have been published in the October issue of the European Journal of Neurology, and include a number of new recommendations and practice points.

These guidelines should be adhered to to improve the diagnosis and management of Alzheimer's disease, said EFNS. The task force working group reviewed evidence from original research articles, meta-analysis and systematic reviews, published before May 2009.

The guidelines state that functional neuroimaging using FDG PET and SPECT may increase diagnostic confidence in the evaluation of dementia.

In a clinical pathological study, a positive perfusion SPECT scan raised the likelihood of Alzheimer's disease to 92 percent, whereas a negative SPECT scan lowered the likelihood to 70 percent. SPECT was more useful when the clinical diagnosis was “possible” Alzheimer's disease, with the likelihood of 84 percent with a positive SPECT, and 52 percent with a negative SPECT.

Dopaminergic SPECT imaging (FP-CIT or DATScan; GE Healthcare, Amersham, U.K.) is useful to differentiate Alzheimer's disease from dementia with Lewy bodies with sensitivity and specificity around 85 percent, according to the guidelines.

The guidelines also mentioned that FDG PET has become a practically applicable tool since the wide distribution of PET/CT machines. It may reveal specific abnormalities in Alzheimer's disease by showing reduced glucose metabolism in the parietal and superior/posterior temporal regions, posterior cingulate cortex and precuneus. In advanced stages of Alzheimer's disease, frontal lobe defects are also seen.

FDG PET has been reported to have a sensitivity of 93 percent and a specificity of 63 percent in predicting a pathological diagnosis of Alzheimer's disease. FDG PET is particularly useful in the differential diagnosis of Alzheimer's disease towards other dementias with specificity higher than 95 percent in early onset cases, according to the guidelines.

FDG PET is reimbursed in the U.S. for the distinction between Alzheimer's disease and fronto-temporal dementia only.

A very promising development is the possibility of imaging amyloid with new PET ligands, but these are not yet available for routine use, stated the guidelines.