Dopamine transporter imaging deficit predicts early transition to synucleinopathy in idiopathic REM sleep behavior disorder

Objective: To determine the usefulness of dopamine transporter (DAT) imaging to identify idiopathic REM sleep behavior disorder (IRBD) patients at risk for short-term development of clinically-defined synucleinopathy. Methods: Eighty-seven patients with polysomnography-confirmed IRBD underwent 123I-FP-CIT DAT-SPECT. Results were compared with 20 matched controls without RBD who underwent DAT-SPECT. In patients, FP-CIT uptake was considered abnormal when values were two standard deviations below controls' mean uptake. After DAT-SPECT, patients were followed-up during 5.7 ± 2.2 (range, 2.6-9.9) years. Results: Baseline DAT deficit was found in 51 (58.6%) patients. During follow-up 25 (28.7%) subjects developed clinically-defined synucleinopathy (Parkinson disease in 11, dementia with Lewy bodies in 13, multiple system atrophy in one) with mean latency of 3.2 ± 1.9 years from imaging. Kaplan-Meier survival analysis showed increased risk of incident synucleinopathy in patients with abnormal DAT-SPECT than with normal DAT-SPECT (20% vs. 6% at three years, 33% vs. 18% at five years; log rank test, p=0.006). Receiver operating characteristics curve revealed that reduction of FP-CIT uptake in putamen greater than 25% discriminated patients with DAT deficit who developed synucleinopathy from patients with DAT deficit that remained disease-free after three years of follow-up. At 5-year follow-up, DAT-SPECT had 75% sensitivity, 51% specificity, 44% positive predictive value, 80% negative predictive value, and like-hood ratio 1.54 to predict synucleinopathy. Interpretation: DAT-SPECT identifies IRBD patients at short-term risk for synucleinopathy. Decreased FP-CIT putamen uptake greater than 25% predicts synucleinopathy after three years follow-up. These observations may be useful to select candidates for disease-modification trials in IRBD. This article is protected by copyright. All rights reserved.