Abstract
Interstitial lung disease (ILD) can occur in any of the connective tissue diseases (CTD) with varying frequency and severity, and an overall long-term prognosis that is less severe than that of idiopathic pulmonary fibrosis (IPF). Because ILD may be the presenting manifestation of CTD and/or the dominant manifestation of CTD, clinical extra-thoracic manifestations should be systematically considered in the diagnostic approach of ILD. When present, autoantibodies strongly contribute to the recognition and classification of the CTD. Patients with clinical extrathoracic manifestations of CTD and/or autoantibodies (especially with a high titer and/or the antibody is considered "highly specific" of an autoimmune condition), but who do not fit with established international CTD criteria may be called undifferentiated CTD or "lung-dominant CTD". Although it remains to be determined which combination of symptoms and serologic tests best identify the subset of patients with clinically relevant CTD features, available evidence suggests that such patients may have distinct clinical and imaging presentation and may portend a distinct clinical course. However, autoantibodies alone when present in IPF patients do not seem to impact prognosis or management. Referral to a rheumatologist and multidisciplinary discussion may contribute to management of patients with undifferentiated CTD.