Background/Purpose: Mixed Connective Tissue Disease (MCTD) is a chronic, immune-mediated disorder defined by the combined presence of serum anti-ribonucleoprotein (RNP) antibodies and selected clinical features of Systemic Sclerosis, Systemic Lupus Erythematosus, Rheumatoid Arthritis and Polymyositis. The prevalence of Interstitial Lung Disease (ILD) in MCTD has been variously reported by previous studies [1]. It is considered to be a major complication in MCTD patients, yet knowledge is scarce regarding the long term progression of ILD in established MCTD.

Methods: Baseline and follow up high-resolution computed tomography (HRCT) of the lungs were systematically reviewed in 113 MCTD patients from the previously described nationwide Norwegian cohort [2]. Patients were included in the cohort if they had a clinical diagnosis of MCTD verified by a rheumatologist; positive serum anti-RNP antibody test and fulfilment of at least one of the following criteria sets: the modified Sharp’s criteria, the Alarcón-Segovia criteria and the Kasukawa critera. The presence of fibrosis was evaluated according to the CT criteria of ILD recommended by The Nomenclature Committee of the Fleischner Society. The extent of fibrosis was determined in 10 HRCT sections and expressed as % of total lung volume.

Results: The mean (SD) time between baseline and follow up lung HRCT in the 113 patients was 7.0 (1.8) years. Mean (SD) disease duration at baseline was 10.0 (8.1) years. Pulmonary fibrosis was present at baseline in 36.3% and at follow-up in 38.0% of the patients. Median (IQR) extent of fibrosis % of total lung volume was 4.0 (7.3) at baseline and 6.3 (14.0) at follow up. There were only two new cases of pulmonary fibrosis at follow up resulting in an incidence proportion of 2.8%. Progression of fibrosis from baseline to follow-up was evident in 20 patients (17.7%). In these 20 patients the median (IQR) annual pulmonary fibrosis progression rate was 0.9 (1.4) % of total lung volume. Univariable logistic regression revealed that no prior arthritis at baseline was predictive of progressive lung disease.

Conclusion: Pulmonary fibrosis is present in a substantial portion of MCTD patients. These results suggest that pulmonary fibrosis generally appears early in the disease and the progression of pulmonary fibrosis years after diagnosis is generally mild and non- or slowly progressive. However a subset of MCTD patients has deteriorating progressive pulmonary fibrosis. The absence of arthritis was found to be a predictor of progressive pulmonary fibrosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/pulmonary-fibrosis-in-mixed-connective-tissue-disease-results-from-an-unselected-longitudinal-cohort/