Interstitial lung disease in rheumatoid or psoriatic arthritis patients initiating biologics, and controls - data from five Nordic registries

OBJECTIVE: Interstitial lung disease (ILD) is one of the most common pulmonary manifestation of rheumatoid arthritis (RA), but its prevalence has not been investigated in psoriatic arthritis (PsA). The role of Methotrexate in ILD development remains debated. This study compares the incidences of ILD in patients with RA or PsA initiating a first biologic disease-modifying antirheumatic drug (bDMARD) to that in the general population and investigates the role of methotrexate co-medication on ILD incidence.

METHODS: Patients were identified in five rheumatology registers. Demographics, methotrexate use, and disease activity were retrieved. Matched subjects from the general population were available from four countries. Incidence of ILD during an up to five-year follow-up was assessed through national patient registries. Subjects with prior ILD were excluded. Adjusted hazard ratios (HR) were calculated for ILD incidence in patients vs. general population, and for methotrexate users vs. non-users.

RESULTS: During follow-up of 29 478 RA patients and 10 919 PsA patients initiating a first bDMARD, and 362 087 population subjects, 225, 23 and 251 cases of ILD were identified, respectively. HRs for ILD (vs. population subjects) were 9.7 (95% CI 8.0, 11.9) in RA and 4.4 (2.8, 7.0) in PsA. HRs for ILD with methotrexate co-medication (vs. non-use) were 0.9 (95% CI 0.7, 1.2) in RA and 1.0 (95% CI 0.2, 2.2) in PsA.

CONCLUSION: Among patients with RA and PsA initiating bDMARD, the risk of ILD was higher than in the general population, highest in RA. Methotrexate co-medication was not a risk determinant for ILD.