Inflammation-induced cysts mimic honeycombing on high-resolution computed tomography in rheumatoid...

Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) often manifests with a usual interstitial pneumonia (UIP) pattern and has a poor prognosis similar to idiopathic pulmonary fibrosis (IPF). Despite radiological similarity to IPF, RA-UIP typically shows greater inflammation. This study aimed to investigate the formation of cysts mimicking honeycombing radiologically in RA-UIP. We hypothesized that the pathogenesis of these cystic structures may differ from that of IPF.

We retrospectively analyzed patients with rheumatoid arthritis who had a UIP/probable UIP pattern on high-resolution computed tomography and underwent surgical lung biopsy. IPF/UIP hallmark features, inflammatory cell infiltration, and inducible bronchus-associated lymphoid tissue (iBALT) in bronchioles and alveoli were assessed, and their contribution to cyst formation was examined. Changes after immunosuppressive therapy were evaluated using the Wilcoxon signed-rank test.

Six patients with RA-UIP were included. No patient showed moderate-to-severe IPF/UIP hallmark features. All patients exhibited moderate-to-severe inflammatory cell infiltration; 83% showed plasma cell infiltration and 67% had iBALT. Moderate-to-severe intralobular bronchiolar destruction and adjacent alveolar structural damage were observed in 67% and 83% of patients, respectively, leading to cyst formation. In treated patients (n = 5), median %FVC increased from 85.7 to 113.6 (P = 0.04) and median %DLCO increased from 64.9 to 89.7 (P = 0.04).

In this small, selected cohort, cyst formation in RA-UIP may result from inflammation-related destruction of small airways and adjacent alveolar structures rather than solely from the fibrotic remodeling typical of IPF/UIP. Immunosuppressive therapy may provide clinical benefit in selected patients.