Fluorine-18 labeled fluorodeoxyglucose positron emission tomography/computed tomography used in diagnosing connective tissue diseases in fever of unknown origin/inflammatory of unknown origin patients

Objective To explore the significance of Fluorine-18 labeled fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in diagnosing connective tissue diseases (CTDs) in fever of unknown origin (FUO) or inflammation of unknown origin (IUO) patients. Methods Clinical and image data of 242 consecutive FUO/IUO patients who underwent PET/CT examination and eventually diagnosed CTDs were retrospectively analyzed, including distribution of diseases, clinical characteristics, and PET/CT imaging findings. The role of FDG PET/CT in differential diagnosis of CTDs was evaluated through clinical questionnaire survey. Results Patients diagnosed as CTDs accounted for 48.1% of FUO/IUO patients. Among them, adult-onset Still's disease was most frequently diagnosed. Other common diseases included systemic vasculitis, undifferentiated connective tissue disease, rheumatoid arthritis, idiopathic inflammatory myopathy, systemic lupus erythematosus, and polymyalgia rheumatica. On FDG PET/CT examination, 97.9% of the patients had positive findings. Inflammatory lesions were detected in 66.5% and non-specific abnormal uptakes were found in 31.4%. Detected lesions distributed consistently with corresponding susceptible organs and tissues in various diseases. Clinical questionnaire results shown that FDG PET/CT excluded malignant tumors, focal infections, or other typical CTDs in 45.5% of the patients; indicated important diagnostic clues or appropriate biopsy sites in 20.6% of patients; and directly suggested the diagnosis of a CTD in 33.1% of patients. Conclusion FDG PET/CT could reveal inflammatory lesions in organs and tissues that reflect the clinical characteristics in different CTDs, thus providing an objective evidence for differential diagnosis, classification, and treatment decision of these diseases.