F-18 FDG PET/CT in Relapsing Polychondritis Patients with Initial Respirotory Symptoms: Imaging Features and Association with Pulmonary Function and Disease Activity

Abstract Background: To summarize F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) imaging features of relapsing polychondritis (RP) and to evaluate the feasibility of imaging parameters in the estimation of pulmonary function and disease activity in a cohort of RP patients with airway involvement.Methods: Thirty RP patients with respiratory symptoms who underwent PET/CT scans before corticosteroid treatment were included. Six patients underwent another post-therapeutic PET/CT scan. Imaging features were described by consensus, and FDG uptake values (SUVmax, PET FDG Burden Score (PETFBS) and PETCTindex) either for global cartilages or for the airway were calculated to correlate with clinical symptoms, pulmonary functional parameters and serological inflammatory markers C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR).Results: Laryngo-tracheo-bronchial involvement was detected by PET/CT for all patients with increased FDG uptake in 28/30 patients. The incidence of positive PET was higher in segments with wall thickening (52.68% vs. 15.48%) but was not associated with calcification or stenosis. A total of 46.7% (14/30) of patients presented with sole respiratory symptoms, while PET/CT revealed additional abnormalities in addition to laryngo-tracheo-bronchia. FDG uptake values negatively correlated with disease duration but not with fever. All FDG uptake values showed a positive correlation with FEV1/FVC, with the highest coefficient for SUVmax in the airway (rs =0.628). CRP and ESR were negatively correlated with PETFBS and PETCTindex but not with SUVmax. The largest Spearman correlation coefficient resulted in PETFBS in the airway (rs =0.67). Re-examination PET/CT in 6 patients revealed partial therapeutic response (n = 4), stable disease (n = 1) and progressive disease (n = 1).Conclusion: PET/CT is a valuable tool for assessing RP with airway involvement, especially for patients who present with sole respiratory symptoms. SUVmax and PETFBS have distinct advantages in the clinical evaluation of RP with respect to pulmonary function and disease activity.