Impact of age correction on the diagnostic performance of the specific binding ratio in dopamine transporter SPECT

Ziel/Aim The striatal I-123-FP-CIT specific binding ratio (SBR) decreases with healthy aging by about 5  % per decade. However, age explains less than 10  % of the SBR variability in healthy subjects aged ≥ 50y. Therefore, the necessity of age correction of the SBR in clinical routine is still a matter of debate. This study tested the impact of age correction on diagnostic SBR performance in three different settings.

Methodik/Methods Research setting: The putaminal SBR of 210 healthy controls (HC) and 446 Parkinson’s disease (PD) patients of the Parkinson’s Progression Marker Initiative (PPMI) was downloaded from the PPMI homepage. Clinical setting A: 186 patients with neurodegenerative parkinsonian syndrome (PS) and 186 patients with non-neurodegenerative PS were recruited retrospectively at one site. The putaminal SBR was obtained by hottest voxels analysis of SPECT images reconstructed by filtered backprojection. Clinical setting B: 84 patients with neurodegenerative PS and 38 patients with non-neurodegenerative PS were recruited retrospectively at another clinical site. The putaminal SBR was obtained by applying anatomical standard ROIs to iteratively reconstructed SPECT images. The minimum of left and right putamen SBR was used in all settings. Age correction was based on linear regression of the putamen SBR with age as independent variable in the HC/non-neurodegenerative PS, separately in each setting. The area (AUC) under the ROC curve for identification of PD/neurodegenerative PS was used as performance measure.

Ergebnisse/Results The AUC without/with age correction was 0.982 (95  %-CI: 0.971–0.992)/0.980 (0.971–0.990) in the research setting, 0.949 (0.927–0.972)/0.945 (0.921–0.969) in clinical setting A, and 0.965 (0.937–0.993)/0.974 (0.950–0.998) in clinical setting B. Only the small loss of AUC by age correction in clinical setting A was significant (DeLong p = 0.029).

Schlussfolgerungen/Conclusions These findings do not support age correction of the [I-123]FP-CIT SBR in the etiological diagnosis of parkinsonian syndromes.