Lung involvement in connective tissue diseases: a comprehensive review and a focus on rheumatoid arthritis

The lungs are frequently involved in Connective Tissue Diseases (CTDs). Interstitial lung disease (ILD) is one of the most common pleuropulmonary manifestations that affects prognosis significantly. In practice, rheumatologists and other physicians tend to underestimate the impact of CTD-ILDs and diagnose respiratory impairment when it has reached an irreversible fibrotic stage. Early investigation, through clinical evidence, imaging and - in certain cases - lung biopsy, is therefore warranted in order to detect a possible ILD at a reversible initial inflammatory stage. In this review, we focus on lung injury during CTDs, with particular attention to ILDs, and examine their prevalence, clinical manifestations and histological patterns, as well as therapeutic approaches and known complications till date. Although several therapeutic agents have been approved, the best treatment is still not certain and additional trials are required, which demand more knowledge of pulmonary involvement in CTDs. Our central aim is therefore to document the impact that lung damage has on CTDs. We will mainly focus on Rheumatoid Arthritis (RA), which - unlike other rheumatic disorders - resembles Idiopathic Pulmonary Fibrosis (IPF) in numerous aspects.