Molecular imaging findings with ¹⁸F-FDG and ⁶⁸Ga-FAPI PET/CT in a case of chronic polyarthralgia

Positron emission tomography (PET) with ¹⁸F-fluorodeoxyglucose for detection of active inflammation is well documented; however, the in vivo visualization of immune-mediated tissue remodeling has not been possible till date. With the recent development of ⁶⁸Ga-fibroblast activation protein inhibitors (FAPI), which specifically binds to the activated fibroblasts located around the synovium allowing for the visualization of mesenchymal and stromal activation process in vivo, it is possible to use this modality to use as an objective indicator of disease activity. We observed increased FAPI uptake around all the large joints of the bilateral upper and lower limbs of a chronic polyarthralgia patient. In view of the specificity of FAPI for the activated fibroblasts, the possibility of future therapeutic approach using FAPI must, therefore, be kept in mind.