Exploring the Novel Value of PSMA PET in Sjögren's Syndrome: Integrated Analysis With Established FAPI PET Imaging

Based on current evidence, salivary gland acinar cells physiologically express PSMA; thus, reduced PSMA uptake may reflect loss of functional parenchyma in patients with pSS. In contrast, activated fibroblasts markedly express FAP, and increased FAPI uptake correlates with ongoing inflammation and fibroblast-driven remodeling. We hypothesize that within the same gland, functional decline (PSMA↓) and inflammatory activity (FAPI↑) may coexist and exhibit a negative correlation, forming a paired imaging biomarker that captures both pathological dimensions. By integrating these two signals into a combined PSMA/FAPI Index, this approach may enable more precise characterization of the "function-inflammation" spectrum in pSS, providing a noninvasive tool for disease staging, monitoring, and potentially predicting therapeutic response.

Inclusion criteria

• Age 18-80 years;
• Fulfillment of the 2016 ACR-EULAR Classification Criteria for pSS at enrollment. OR diagnosis of a solid tumor scheduled for FAPI PET imaging

Exclusion criteria

• Combined with tumors or other connective tissue diseases (for SS group);
• Patients who are currently using hormones/biological agents (for both groups)；
• Pregnancy or lactation