The Lung in Rheumatoid Arthritis: Focus on Interstitial Lung Disease.

Interstitial lung disease (ILD) is an increasingly recognized complication of rheumatoid arthritis (RA) and is associated with significant morbidity and mortality. In addition, approximately one-third of patients have subclinical disease with varying degrees of functional impairment. Although risk factors for RA-related ILD are well established (e.g., older age, male sex, ever smoking, and seropositivity for rheumatoid factor and anti-cyclic citrullinated peptide), little is known about optimal disease assessment, treatment, and monitoring, particularly in patients with progressive disease. Patients with RA-related ILD are also at high risk of infection and drug toxicity, which, along with comorbidities, complicates further treatment decision-making. There are distinct histopathologic patterns of RA-related ILD with different clinical phenotypes, natural histories, and prognoses. Of these, the usual interstitial pneumonia (UIP) subtype of RA-related ILD shares a number of clinical and histopathologic features with idiopathic pulmonary fibrosis, the most common and severe of the idiopathic interstitial pneumonias, suggesting the existence of common mechanistic pathways and possibly therapeutic targets. There remain substantial gaps in our knowledge of RA-related ILD. Concerted multinational efforts by expert centers has the potential to elucidate the basic mechanisms underlying RA-related UIP and other subtypes of RA-related ILD and facilitate the development of more efficacious and safer drugs.