Discordant 68 Ga-FAPI and 18 F-FDG Uptake in Reactive Lymph Nodes in a Case of Esophageal Cancer and Systemic Lupus Erythematosus.

This case is a 54-year-old woman with systemic lupus erythematosus (SLE) and distal esophageal squamous cell carcinoma (SCC) who showed inconsistent uptake patterns on 18 F-FDG and 68 Ga-FAPI PET/CT. 18 F-FDG PET/CT revealed diffuse uptake in the enlarged axillary lymph nodes as well as mild increased uptake in the bilateral inguinal and cervical, and mediastinal uptake, beyond the uptake in the esophageal tumor (SUVmax 19.85). A week later, FAPI PET/CT showed negligible uptake in the axillary nodes but strong uptake in the main tumor. These lymph nodes' histopathology showed reactive hyperplasia. This pattern of 18 F-FDG PET/CT has been previously described in a few cases of SLE patients mimicking lymphoma; however, this case also underscores the potential high specificity of FAPI in distinguishing inflammatory from metastatic lymph node disease.