Salivary Gland Uptake on 18F-FP-CIT PET as a New Biomarker in Patients With Parkinsonism

Objective: 18F-FP-CIT positron emission tomography (PET) is known for its high sensitivity and specificity for evaluating striatal dopamine transporter (DAT) binding. Recently, for the early diagnose of Parkinson's disease, many researchers focused on the diagnosis of synucleinopathy in organs involved in non-motor symptoms of Parkinson's disease. We investigated the feasibility of salivary gland uptake on 18F-FP-CIT PET as a new biomarker in patients with parkinsonism. Materials and Methods: A total of 219 participants with confirmed or presumed parkinsonism, including 54 clinically diagnosed idiopathic Parkinson's disease (IPD), 59 suspected and yet undiagnosed, and 106 with secondary parkinsonism, were enrolled. The standardized uptake value ratio (SUVR) of the salivary glands was measured on both early and delayed 18F-FP-CIT PET scans using the cerebellum as the reference region. Additionally, the delayed-to-early ratio (DE_ratio) of salivary gland was obtained. The results were compared between patients with different PET patterns. Results: The SUVR in early 18F-FP-CIT PET scan was significantly higher in patients with IPD pattern compared that in the non-dopaminergic degradation group (0.5 & PLUSMN; 0.19 vs. 0.6 & PLUSMN; 0.21, P < 0.001). Compared with the non-dopaminergic degradation group, the DE_ratio was significantly lower in patients with IPD (5.05 & PLUSMN; 1.7 vs. 4.0 & PLUSMN; 1.31, P < 0.001) or atypical parkinsonism patterns (5.05 & PLUSMN; 1.7 vs. 3.76 & PLUSMN; 0.96, P < 0.05). The DE_ratio was moderately and positively correlated with striatal DAT availability in both the whole striatum (r = 0.37, P < 0.001) and posterior putamen (r = 0.36, P < 0.001). Conclusion: Parkinsonism patients with an IPD pattern exhibited a significant increase in uptake on early 18F-FP-CIT PET and a decrease in the DE_ratio in the salivary gland. Our findings suggest that salivary gland uptake of dual-phase 18F-FP-CIT PET can provide diagnostic information on DAT availability in patients with Parkinson's disease.