Lung involvement and drug-induced lung disease in patients with rheumatoid arthritis

Interstitial lung disease (ILD) is a common extra-articular manifestation of rheumatoid arthritis (RA) and a significant cause of morbidity and mortality. Usual interstitial pneumonia and nonspecific interstitial pneumonia seem to be the most frequent patterns in RA patients with ILD, although the proportion of patients with usual interstitial pneumonia is higher than among patients with other systemic rheumatic autoimmune diseases. RA patients with ILD most frequently present with chronic symptoms of cough and dyspnea when climbing stairs or walking uphill. A physical examination may reveal inhalatory crackles and a pulmonary function test demonstrates restrictive physiology, often with reduced diffusing capacity. High-resolution computed tomography is generally sufficient to confirm a diagnosis of ILD, although a minority of cases may require a surgical lung biopsy. Conventional disease-modifying antirheumatic drugs such as methotrexate (MTX) or leflunomide (LEF) and biological agents such as TNF-blocking agents or rituximab may trigger or aggravate ILD in RA patients, and infections may contribute to increased mortality in such patients. LEF should not be used in patients with a history of MTX pneumonitis. The prevalence of interstitial pneumonia among RA patients treated with anti-TNF agents ranges from 0.5 to 3%; however, as the evidence that anti-TNF increases or decreases the risk of ILD is controversial, it is not clear whether this indicates more severe RA requiring biological therapy or the effect of exposure to potentially toxic drugs such as MTX or LEF. The development of treatment-related ILD is a paradoxical adverse event, and patients should be warned about this rare but serious complication of biological or disease-modifying antirheumatic drug therapy.