AB0833 THE USE OF F-18 FDG PET/CT AND Ga-68 PSMA PET/CT IN THE EVALUATION OF SALIVARY GLANDS IN SJÖGREN’S SYNDROME
Authors: A. Avcu, K. Oksuzoglu, T. N. Kissa, T. Y. Erdil, G. Mumcu, G. Bruyn, T. Ones, N. Inanc
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Sjögren's syndrome (SjS) is a chronic systemic disease mainly involving the salivary and lacrimal glands. Noninvasive imaging modalities for the evaluation of salivary glands include salivary gland scintigraphy, ultrasound, and magnetic resonance imaging (MRI). Galyum-68 PSMA positron emission tomography/computed tomography (Ga-68 PSMA PET/CT) imaging is mainly used for the evaluation of prostate malignancies. In addition, promising results have been reported in the literature with Ga-68 PSMA PET/CT to demonstrate major salivary gland function. The value of 18F-fluorodeoxyglucose positron emission tomography/computer tomography (F-18 FDG PET/CT) for evaluating salivary glands in SjS remains inconclusive. <h3>Objectives:</h3> The aim of this study was to evaluate salivary gland with F-18 FDG PET/CT, Ga-68 PSMA PET/CT and to compare it with salivary gland ultrasound and unstimulated salivary flow rate. <h3>Methods:</h3> The study included 23 primary and secondary SjS patients (22 females, 1 male; age &gt;18 years) who underwent F-18 FDG PET/CT in the last 6 months for any reason at Marmara University Pendik Training and Research Hospital. All met the diagnosis of SjS according to ACR/EULAR 2016 classification criteria. Afterwards, Ga-68 PSMA PET/CT was performed with the consent of the patients. FDG SUVmax, FDG SUVmean, PSMA SUVmax, PSMA SUVmean, PSMAvolume and PSMA SUVmeanXvolume values of each parotid and submandibular salivary gland were obtained. Salivary gland ultrasound was performed at the time of recruitment. Of each of the parotid and submandibular salivary glands, the homogeneity, the presence of hypoechoic areas and hyperechoic bands, and the clarity of the borders of the glands were evaluated and scored with both Hocevar and the OMERACT scoring system. OMERACT is a semiquantitative scoring system based on the presence and extent of hypoechoic areas in the salivary glands (0-3). Salivary flow rates of patients were measured at their last visits. The parameters obtained from F-18 FDG PET/CT and Ga-68 PSMA PET/CT were compared with both ultrasound scores and unstimulated salivary flow rate. <h3>Results:</h3> The mean age of the 23 patients included in the study was 57.5±8.8 years and 95% (n=22) were female. 18 patients had primary SjS and 5 had secondary SjS. The mean duration of disease was 7.48±4.7 years. Unstimulated salivary flow rate was below ≤0.1 mL/m in 65% (n=15) of the patients. In ultrasonographic evaluation, the rates of hypoechoic areas, hyperechoic bands, and OMERACT score grade 2 or 3 were 38% (n=16), 33% (n=14), and 38% (n=16) in parotid glands, and 52% (n=22), 42% (n=18), and 52% (n=22) in submandibular glands, respectively. OMERACT and items of Hocevar ultrasound scores were divided into two categories as 0-1 and 2-3 and compared with values of F-18 FDG PET/CT, Ga-68 PSMA PET/CT in parotid and submandibular glands. Tables 1 and 2 show the median values of Ga-68 PSMA PET/CT and F-18 FDG PET/CT as well as the results of comparing these parameters to ultrasonography scores.PSMA SUVmax, SUVmean, and SUVmeanXvolume are all lower with higher ultrasonography scores in both the parotid and submandibular glands (Table 1). F-18 FDG PET/CT SUVmax and SUVmean values are higher in parotid glands with higher ultrasonography scores compared to submandibular glands, with a lower percentage of hyperechoic (fibrotic gland) parotid glands (33% vs. 42%) (Table 2). There was no correlation between unstimulated salivary flow rates and Ga-68 PSMA PET/CT parameters, but there was a correlation with parotid gland FDG SUVmean ((r= 0.486, p= 0.03), submandibular gland FDG SUVmax (r= 0.562, p= 0.01) and FDG SUVmean (r= 0.494, p= 0.02) values. <h3>Conclusion:</h3> Ga-68 PSMA PET/CT can be used as an adjunctive imaging modality to demonstrate pathologic salivary glands in SjS patients, whereas F-18 FDG PET/CT is better for estimating fibrotic glands with low unstimulated salivary flow rates. This study also strengthened the role of salivary gland ultrasound in the evaluation of salivary glands in patients with SjS, both in terms of pathology and function. <h3>REFERENCES:</h3> <b>NIL.</b> <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> <b>None declared.</b>