Rheumatoid arthritis and lung disease: from mechanisms to a practical approach

Rheumatoid arthritis (RA) is a common chronic systemic autoimmune disease characterized by joint inflammation and, in a proportion of patients, extra-articular manifestations (EAM). Lung disease, either as an EAM of the disease, related to the drug therapy for RA, or related to comorbid conditions, is the second commonest cause of mortality. All areas of the lung including the pleura, airways, parenchyma, and vasculature may be involved, with interstitial and pleural disease and infection being the most common problems. High-resolution computed tomography of the chest forms the basis of investigation and when combined with clinical information and measures of physiology, a multidisciplinary team can frequently establish the diagnosis without the need for an invasive biopsy procedure. The most frequent patterns of interstitial lung disease (ILD) are usual interstitial pneumonia (UIP) and nonspecific interstitial pneumonia (NSIP), with some evidence for the prognosis being better than for the idiopathic equivalents. Risk factors depend on the type of disease but for ILD (mainly UIP and NSIP) include smoking, male gender, human leukocyte antigen haplotype, rheumatoid factor, and anticitrullinated protein antibodies (ACPAs). Citrullination of proteins in the lung, frequently thought to be incited by smoking, and the subsequent development of ACPA appear to play an important role in the development of lung and possibly joint disease. The biologic and nonbiological disease modifying antirheumatic drugs (DMARDs) have had a substantial impact on morbidity and mortality from RA, and although there multiple reports of drug-related lung toxicity and possible exacerbation of underlying ILD, overall these reactions are rare and should only preclude the use of DMARDs in a minority of patients. Common scenarios facing pulmonologists and rheumatologists are addressed using the current best evidence; these include screening the new patient; monitoring and choosing RA treatment in the presence of subclinical disease; treating deteriorating ILD; and establishing a diagnosis in a patient with an acute respiratory presentation.