Is 18F-FDG PET/CT useful for diagnosing relapsing polychondritis with airway involvement and monitoring response to steroid-based therapy?

BACKGROUND

18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is a promising tool for diagnosing relapsing polychondritis (RP). However, its usefulness in assessing RP with airway involvement is unknown.

OBJECTIVE

This study aimed to further evaluate and confirm the potency of 18F-FDG PET/CT in diagnosing RP with airway involvement and monitoring response to steroid-based therapy.

METHODS

A total of 30 patients from a dedicated respiratory centre, diagnosed with RP in accordance with McAdam, Damiani or Levine criteria, were included in this study. All patients underwent baseline 18F-FDG PET/CT, and 10 patients underwent second scans after 2.5-15 months of steroid-based therapy. Visual scores (VS) and maximal standard uptake values (SUVmax) were analysed.

RESULTS

In the initial scan, 83.3% (25/30) of patients were found to have FDG uptake in more than one cartilage. The median VS and SUVmax in the cartilages were 3 (range, 1-3) and 3.8 (range, 1.9-17.9), respectively. Positive rates for PET/CT-guided biopsy in nasal, auricular, and tracheal/bronchial cartilages were 100% (5/5), 88.9% (8/9), and 10.5% (2/19), respectively, but the positive biopsy rate in the auricular cartilage was 92.3% (12/13) even without PET/CT assessment. Based on biopsy-proven sites, the sensitivity of PET/CT was 55.6%, and the specificity was 5.3%. Compared with the baseline scan, the second scan showed much lower median VS (2 vs 3, respectively; p < 0.0001) and SUVmax (2.9 vs 3.8, respectively; p < 0.001). Of 10 patients who underwent second PET/CT, 8 had complete therapeutic response, while 2 had partial response.

CONCLUSION

18F-FDG PET/CT assists in identifying multiple cartilage involvement in RP, but it seems neither a sensitive nor specific modality in diagnosing RP with airway involvement. Moreover, PET/CT has limited utility in locating biopsy sites and monitoring therapeutic response to corticosteroids.