PO:36:238 | Clinical, functional, and radiological similarities between interstitial lung disease–anti–myeloperoxidase and idiopathic pulmonary fibrosis

Enrico Colombo¹, Jessica Gozzi², Paolo Francia³, Giulia Cervi², Marilena Frigato¹, Martina Garuti², Francesca Bartoli¹, Irene Gavioli¹, Caterina Cerbone², Massimiliano Beccaria², Maria Teresa Costantino¹ | ¹SC Allergologia, Immunologia Clinica e Reumatologia, ASST Mantova; ²SC Pneumologia, ASST Mantova; ³SC Radiologia, ASST Mantova, Italy

Background. An association between interstitial lung disease (ILD) and anti–myeloperoxidase (MPO) antibody positivity is well established. This condition does not necessarily overlap with ANCA-associated vasculitis but in 60–70% of cases presents as an isolated pulmonary disease. Previous observations suggested that this fibrosing disorder (MPO-ILD) shares several clinical features with idiopathic pulmonary fibrosis (IPF). Radiologically, small case series reported the presence of honeycomb-like lesions in the anterior segment of the upper lobe and a possible larger size of honeycombing cysts, as suggested by expert radiologists. Based on these findings, we conducted an exploratory comparative study between MPO-ILD and IPF aimed at identifying potential clinical, functional, and radiological differences.

Materials and Methods. We retrospectively enrolled patients followed at the tertiary referral clinics for interstitial lung disease and rheumatology, diagnosed with IPF or MPO-ILD. Clinical data (demographics, comorbidities, treatments, environmental exposures), laboratory findings (autoantibody profiles, CRP, baseline neutrophil count, creatinine), and pulmonary function parameters (FVC, TLC, DLCO) were collected. High-resolution CT (HRCT) scans at diagnosis and after 24 months were reviewed by an expert thoracic radiologist using a structured evaluation grid. A specific index was developed to assess honeycombing cyst size, based on the mean diameter of three cysts per lung side.

Results. A total of 27 IPF and 5 MPO-ILD patients were included; two MPO-ILD patients developed vasculitis after the ILD diagnosis. Demographic, exposure, and comorbidity profiles were comparable between groups. Compared to IPF, MPO-ILD patients more frequently reported arthralgia and ENT symptoms (p = 0.009 and 0.008, respectively). At baseline, MPO-ILD patients had higher serum creatinine (p = 0.012) and neutrophil counts (p = 0.012). Low-titer ANA positivity was more frequent in MPO-ILD (18.5% in IPF vs 80% in MPO-ILD, p = 0.015). No relevant differences were observed in FVC or TLC between groups; however, an improvement in DLCO was noted in MPO-ILD patients during the first 12 months (p = 0.047). All MPO-ILD patients received corticosteroids, 4/5 received immunosuppressive therapy, 3/5 were treated with nintedanib, and 1/5 with pirfenidone. At chest CT review, most patients exhibited a definite or probable UIP pattern (81% IPF and 80% MPO-ILD at 24 months). No radiological item significantly differed between groups, either at baseline or after 24 months.

Conclusions. MPO-ILD is a progressive fibrosing lung disease showing clinical and radiological features largely overlapping with IPF and not invariably associated with vasculitis. A transient improvement in DLCO may reflect the effect of corticosteroid or immunosuppressive therapy during the first 12 months; however, the subsequent decline appears similar to that observed in IPF.