FDG PET imaging in patients with pathologically verified dementia

The purpose of this study was to confirm with pathologic verification 2 bel iefs related to Alzheimer's disease (AD): (a) the long-standing impression that bilateral temporo-parietal hypometabolism, as noted on FDG PET imaging , is the metabolic abnormality associated with Alzheimer's disease (AD) and (b) that the sensitivity, specificity, and diagnostic accuracy of the meta bolic pattern of bilateral temporo-parietal hypometabolism allows different iation between other degenerative causes of dementia. Methods: Twenty two i ndividuals (8 women, 14 men) with difficult-to-characterize memory loss or dementia (using standard clinical criteria), and who eventually received pa thologic confirmation of diagnosis, were evaluated. FDG PET brain scans wer e obtained and visually graded by an experienced nuclear medicine physician as to the presence of classic bilateral temporo-parietal hypometabolism as seen in Alzheimer's type dementia. Sensitivity, specificity, positive pred ictive value, negative predictive value, and diagnostic accuracy of the met abolic pattern of bilateral temporo-parietal hypometabolism were determined using pathologic diagnosis as the gold standard. Results: The clinical dia gnosis of possible or probable AD was determined as the primary cause of de mentia in 12 patients. The sensitivity and specificity of the clinical diag nosis for probable AD were 63% and 100%, respectively. The sensitivity and specificity of the clinical diagnosis for possible and probable AD were 75% and 100%, respectively. The sensitivity, specificity, and diagnostic accur acy of bilateral temporo-parietal hypometabolism being associated with AD w ere 93%, 63%, and 82%, respectively. Conclusion: This study confirms that b ilateral temporo-parietal hypometabolism is indeed the classic metabolic ab normality associated with AD. Furthermore, in individuals with dementia who se FDG PET scans indicated a metabolic pattern other than bilateral temporo -parietal hypometabolism, a cause of dementia other than AD should be suspe cted. These observations may be of clinical importance in differentiating d ementia syndromes. The sensitivity, specificity, and diagnostic accuracy of FDG PET are acceptable as tests to be used in the evaluation of dementia a nd particularly to confirm the clinical suspicion of AD.