Imaging features and clinical value of F-FDG PET/CT for predicting airway involvement in patients with relapsing polychondritis.

Background: The clinical value of F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in assessing relapsing polychondritis (RP) with airway involvement remains controversial. This study aimed to investigate PET/CT features of RP with airway involvement and explore its clinical value in predicting disease pattern, severity and prognosis.

Methods: RP patients with airway involvement who underwent PET/CT from January 2010 to July 2022 were retrospectively reviewed. PET/CT features were analyzed both visually and semiquantitatively with the maximum standardized uptake value (SUVmax) and total lesion glycolysis (TLG). Patterns of airway involvement on PET were summarized. Correlations of SUVmax and TLG of the airway were made with spirometric indicators and serological inflammatory markers (CRP and ESR). In addition, long-term follow-up was conducted through questionnaires in regard to symptom control, subjective feeling, pulmonary function, and quality of life.

Results: Fifty-two cases were finally included. F-FDG PET showed FDG-avid lesions with increased FDG uptake in the airway among 94.2% of the patients. Three patterns (focal, multifocal and diffuse patterns) were identified. TLG of the whole airway was lower in patients with previous therapy (p = 0.046). Bronchoscopy was more sensitive in detecting tracheal abnormalities (90.7% vs.53.5%, p = 0.039) but less sensitive for peripheral airway lesions (65.1% vs. 79.1%, p = 0.046) compared with PET. SUVmax and TLG of the airway positively correlated with spirometry indicators (FEV1%pred, FEV1/FVC, MEF 50%pred, etc.) and serological inflammatory markers. Five patients died during the follow-up, with two deaths related to airway problems. Higher FDG uptake predicted worse subjective feeling, but not with symptom control or pulmonary function.

Conclusion: PET/CT is a valuable tool for RP with airway involvement, particularly in assessing peripheral airway lesions, and PET/CT related parameters are significantly associated with disease patterns, severity, and long-term outcomes.