¹⁸ F-FDG PET/CT and ^99m Tc-HFAPI SPECT/CT in a case of systemic sclerosis-associated interstitial lung disease

Interstitial lung disease (ILD) is a common manifestation of connective tissue disease (CTD) and a substantial contributor to increased morbidity and mortality. ¹⁸ F-fluorodeoxyglucose ( ¹⁸ F-FDG) PET/CT and ^99m Tc-HYNIC-fibroblast activation protein inhibitor ( ^99m Tc-HFAPI) SPECT/CT were performed on a 25-year-old female patient with systemic sclerosis-associated ILD. Baseline imaging demonstrated increased uptake of both tracers in the peripheral lung parenchyma. After corticosteroids and antifibrotic agent treatment, worsening respiratory symptoms and declining pulmonary function were observed. Follow-up imaging showed reduced FDG uptake but increased and expanded HFAPI uptake, with no significant changes on high-resolution CT (HRCT). The discrepancy between FDG and HFAPI uptake indicated the heterogeneous fibrotic and inflammatory processes occurring in individual patients.