Rheumatoid arthritis associated interstitial lung disease: 1 year is too much to exclude methotrexate-induced pulmonary involvement.

Sir,

We read the article, “Pulmonary involvement in rheumatoid arthritis: A cross-sectional study in Iran” by Zayeni et al.[1] with great interest. The authors have evaluated 44 patients of rheumatoid arthritis with pulmonary function testing (PFT), chest X-ray, high-resolution computed tomography (HRCT) of the lungs, and disease activity score 28. The authors have excluded the patients with history of smoking and use of drugs such as gold, penicillamine, sulfasalazine, and methotrexate for more than 1 year.

Rheumatoid arthritis associated interstitial lung disease (RA-ILD) is more commonly found in male, history of smoking, and high titers of rheumatoid factor and with duration of the disease.[2] In the present study, the male are under-represented (9 patients, 20.45%) and smokers have been excluded totally. Thus, the study has significant selection bias.

Studies suggest that methotrexate-induced ILD is most frequently occurs after 4–6 months after initiation of therapy.[34] The authors tried to exclude methotrexate-induced ILD by exclusion of patients taking methotrexate for more than 1 year. While this did not exclude patients having methotrexate-induced ILD, it might have excluded patients having long duration of RA which is linked with development of RA-ILD.

Second, the authors mentioned HRCT findings as nodules, fibrosis, cyst, bronchiectasis, air trapping, and bronchiolectasia. However, RA-ILD is classically divided into usual interstitial pneumonia (UIP), nonspecific interstitial pneumonia, organizing pneumonia, lymphocytic interstitial pneumonia (LIP), bronchiolitis, etc. Hence, the present study lacks these specific patterns of ILD which are recognized worldwide. According to available literature, UIP is the most common form of ILD in RA.[2]

Third, the authors have stated that “air trapping” was the most common finding in patient's PFT, and there is no mention of PFT variables in the present study. Instead of simply summarizing these PFT findings, the authors could have mentioned the PFT variables which would be more helpful for quantification and severity grading of lung function.

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