Clinical utility of 18F-FDG PET/CT in patients with microscopic polyangiitis and interstitial lung disease: a...

We investigated the diagnostic and prognostic value of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) for interstitial lung disease (ILD) in patients with microscopic polyangiitis (MPA).

In this single-centre observational study, 61 patients with MPA who underwent high-resolution computed tomography (HRCT) and 18F-FDG PET/CT were included. ILD diagnosis was based on HRCT. 18F-FDG uptake in the lung parenchyma was assessed as a binary variable (present/absent). Diagnostic performance was evaluated by sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). The prognostic value was determined by Δ (1-year-baseline; positive=improvement) in forced vital capacity (FVC) and diffusing capacity of the lung for carbon monoxide (DLCO) using multivariable linear regression models.

18F-FDG uptake showed high specificity and PPV (both 1.00) but limited sensitivity (0.63) and NPV (0.26) for ILD detection. Patients with 18F-FDG uptake demonstrated significantly greater Δ in FVC (β=8.26 [2.87-13.64], p=0.004) and DLCO (β=7.38 [0.06-14.69], p=0.048) compared with those without uptake. The prognostic value of 18F-FDG uptake was greater than that of the ILD pattern determined by HRCT (usual interstitial pneumonia [UIP] vs. non-UIP). While non-UIP patterns were associated with favourable Δ in FVC (β=8.02 [0.66-15.38], p=0.034), they were not associated with significant changes in DLCO (β=0.66 [-8.83-10.16], p=0.885).

18F-FDG PET/CT demonstrated high specificity but limited sensitivity for detecting ILD in MPA, limiting its use as a screening tool. However, given its prognostic value, 18F-FDG PET/CT could be considered as a complementary imaging modality may aid prognostic stratification in MPA-associated ILD.