No abstract

IgG4-RD is a systemic inflammatory and sclerosing disease. Parotid and lacrimal involvement (formerly called Mikulicz's disease), lymphadenopathy and pancreatitis are the most common manifestations. Patients with IgG4-RD showed favourable responses to treatment with glucocorticoids and immunosuppressive agents.

IgG4-related disease (IgG4-RD) is characterized by lymphoplasmacytic infiltration enriched in IgG4-positive plasma cells and variable degrees of fibrosis with a characteristic storiform pattern. Since fibrosis is an important feature of IgG4-RD, we performed a prospective cohort study to evaluate the performance of 68 Ga-FAPI, a recently introduced PET agent targeting fibroblast activation protein, in IgG4-RD. Methods: Twenty-six patients with IgG4-RD were recruited. All patients underwent both 68 Ga-FAPI and 18 F-FDG PET/CT. The positive rates of the PET/CT scans in the involved organs and the uptake values were compared. Results: In a total of 136 organ involvements in the 26 patients, 68 Ga-FAPI PET/CT additionally detected 18/136 (13.2%) organ involvements in 13/26 (50.0%) patients compared with 18 F-FDG PET/CT. 68 Ga-FAPI PET/CT had a higher positive rate than 18 F-FDG PET/CT in detecting involvement in the pancreas, bile duct/liver, and lacrimal gland. 68 Ga-FAPI also demonstrated significantly higher uptake than 18 F-FDG in the matched disease in the pancreas, bile duct/liver, and salivary gland (p < 0.01). However, lymph node involvements with flip-flop uptake of 18 F-FDG were not accumulating 68 Ga-FAPI. Conclusions: 68 Ga-FAPI might be a promising imaging agent for the assessment of IgG4-RD.