Interstitial Lung Disease in Mixed Connective Tissue Disease: A Single-Center Cohort Study

Abstract

BACKGROUND: Mixed connective tissue disease is a rare systemic autoimmune condition characterized by overlapping features of different connective tissue diseases and the presence of anti-U1-ribonucleoprotein antibodies. Its association with interstitial lung disease represents one of the main causes of morbidity and mortality in affected patients.

OBJECTIVE: To characterize the clinical, immunological, and radiological phenotype of patients with mixed connective tissue disease-associated interstitial lung disease, and to evaluate the evolution of pulmonary function over time.

METHODS: All patients had at least one high-resolution computed tomography scan and two pulmonary function tests available during the 48 ± 12 months follow-up period. The extent of lung involvement was assessed using semi-quantitative visual evaluation of high-resolution computed tomography scans. Severe progression was defined as an annual ≥10% absolute decline in forced vital capacity or a ≥15% absolute decline in diffusion capacity of the lungs for carbon monoxide.

RESULTS: Thirteen patients were included. Raynaud’s phenomenon, puffy fingers, and arthritis were the most common manifestations. Anti-SSA/Ro antibodies were detected in 4 patients. Dyspnea was reported in 7 patients. The predominant radiological pattern was nonspecific interstitial pneumonia, present in 9 patients. Three patients exhibited interstitial lung disease involvement >20%. At baseline, mean predicted FVC and DLCO values were significantly reduced (72.7% ± 17.3% and 58.0% ± 11.9%, respectively). Throughout follow-up, there was a mean increase of 2.5% ± 8.3% in forced vital capacity and a mean decrease of 2.2% ± 11.0% in total lung capacity; diffusion capacity of the lungs for carbon monoxide remained unchanged, with a mean variation of -0.5% ± 10.6%. A total of two patients experienced major interstitial lung disease progression during the follow-up period.

CONCLUSIONS: In this cohort, pulmonary function remained relatively stable over time, with few cases of severe pulmonary function decline, suggesting a slow progression of interstitial lung disease in mixed connective tissue disease.