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The incremental diagnostic value of 18F-florbetapir imaging in naturalistic patients with cognitive impairment: The India-FBP study

      Background

      The 18F-Florbetapir PET amyloid tracer, recently approved by FDA and EMA, has a relatively long radioactive half-life (110-min), making amyloid imaging logistically feasible. However, the added diagnostic value is unclear. We aim to evaluate the incremental diagnostic value of 18F-Florbetapir amyloid PET on top of routine assessment for diagnosis of cognitive impairment.

      Methods

      The study, completed in December 2014, includes 26 Healthy elderly Controls (HC) and 228 patients with a diagnostic probability of Alzheimer Disease (AD) between 15% and 85% accessing 20 Italian memory clinics. Patients complete their diagnostic work-up according to usual local practice. Physicians formulate a clinical diagnosis and rate their diagnostic confidence (0-100%). Patients and HC then undergo amyloid PET with 18F-Florbetapir; diagnoses and diagnostic confidence are revised. Diagnostic confidence increase was evaluated by Wilcoxon Signed Rank Test.

      Results

      To date, data from 140 patients were processed. Of these, before PET scan, 95 patients were diagnosed with AD (Table 1); 27 with FrontoTemporal Disease (FTD; Table 2); 3 with Lewy Body Disease (LBD; Table 3); 10 with Vascular Dementia (VD), Parkinson’s Disease Dementia (PDD), and Cortical Basal Degeneration (CBD); and 5 with other pathologies. Thirty AD (31.6%) tested negative to amyloid-imaging. Positive scans occurred in 11 FTD (40.7%), in 2 LBD (66.7%), in 7 VD-PDD-CBD (70%), and in 4 HC (15.4%). 75% of positive HC were men aged over 69 (Figure 1). The diagnosis after amyloid-imaging was changed in: 86.7% of AD with negative scan; 90.9% of FTD, 50% of LBD and 100% of VD with positive scan. The diagnostic confidence increased significantly after amyloid-PET for both patients with confirmed diagnosis of AD (11.8% increase V=49, p<.05; Figure 2) and those with confirmed diagnosis of non-AD (13.6% increase; V=0, p<.05; Figure 3). 243 PET scans were evaluated by two nuclear medicine physicians, who disagreed on 32 cases (rate of concordance: 86.8%).

      Conclusions

      Data are in line with previous reports. Based on preliminary results, amyloid PET with 18F-Florbetapir has a significant impact on diagnosis and diagnostic confidence of dementia experts.
      Table 1Diagnosis after PET in 95 patients with a clinical diagnosis of AD before PET.
      Diagnosis after PETAmy PETAβ-
      Aβ+
      Same (AD)63 (96.9%)4 (13.3%)
      FTD1 (1.5%)5 (16.7%)
      VD-13 (43.3%)
      LBD1 (1.5%)-
      SNAP-3 (10%)
      Other-5 (16.7%)
      Total65 (100%)30 (100%)
      Table 2Diagnosis after PET in 27 patients with a clinical diagnosis of FTD before PET.
      Diagnosis after PETAmy PET
      Aβ-Aβ+
      AD2 (12.5%)10 (90.9%)
      Same (FTD)12 (75%)1 (9.1%)
      VD2 (12.5%)-
      Total16 (100%)11 (100%)
      Table 3Diagnosis after PET in 3 patients with a clinical diagnosis of LBD before PET
      Diagnosis after PETAmy PET
      Aβ-Aβ+
      AD-1 (50%)
      Same (LBD)1 (100%)1 (50%)
      Total1 (100%)2 (100%)
      Figure thumbnail fx1
      Figure 1HC divided by age and amy-PET result. In red HC Aβ+ and in blue HC Aβ-.
      Figure thumbnail fx2
      Figure 2Increase in diagnostic confidence in patients with a confirmed diagnosis of AD.