Clinical utility of amyloid PET for differential diagnosis of dementia in a typical memory clinical population.

Objectives: PET permits the in vivo detection of the cerebral beta-amyloid (Aβ) pathology as a hallmark of Alzheimer’s disease (AD). Therefore, Aβ PET may improve the differential diagnosis of dementias. However, actual data from real-life clinical populations supporting this expectation is limited. The present study evaluated the added value of Aβ PET beyond the clinical diagnosis alone and FDG PET alone in a typical memory clinic population.

Methods: From our clinical registry 138 cognitively impaired patients who received [18F]FDG and [11C]PIB PET were identified. Eighty-four of these were clinically diagnosed as major cognitive disorder and included into the analysis. Baseline clinical diagnoses (time of PET) and FDG PET ratings were established in a standardized, rater-blinded procedure without and with access the Aβ PET result. Diagnoses were dichotomized into AD or non-AD dementia. The added value of Aβ PET in terms of diagnostic accuracy was evaluated. An interdisciplinary consensus diagnosis incorporating all available information over a follow-up of 2.4 ± 1.3 years after PET served as reference.

Results: With additional knowledge of the Aβ PET result, diagnostic accuracy of clinical diagnosis and FDG PET improved from 71% to 89% and from 76% to 94%, respectively (p < 0.0005, McNemar tests). Gain in diagnostic accuracy was comparable in older (> 68.4 years; 19% improvement for clinical, 23% for FDG PET ratings) and younger patients (17% improvement for clinical, 12% for FDG PET ratings). Accuracy of the combined approaches (clinical diagnosis plus Aβ PIB, FDG plus Aβ PET) was higher in younger patients (93% and 98%) than in older patients (86% and 90%).

Conclusion: Amyloid PET improves the accuracy of the differential diagnosis of dementia, irrespective of the patients’ age, which is at variance with the recommendation given by the current Appropriate Use Criteria (Johnson et al., 2013). Research Support: -