Clinical Presentation of Connective Tissue Disease Patients with and without Interstitial Lung Disease: A Retrospective Study

Background: Connective tissue diseases (CTDs) are responsible for about 20% of interstitial lung disease (ILD) cases, but their diagnosis in a pulmonary unit (PU) is not always straightforward due to a heterogeneous clinical picture. Objectives: The aim of this study was to evaluate the clinical presentation of rheumatoid arthritis (RA) and CTD-ILD cases diagnosed in PU, compared to RA and CTD patients diagnosed in a rheumatologic unit (RU). Methods: Patients with RA, systemic sclerosis (SSc), primary Sjӧgren's syndrome (pSS), and idiopathic inflammatory myopathy were retrospectively enrolled from an RU and a PU designated to manage ILD during a period from January 2017 to October 2022. The classification of CTD-PU was carried out in a multidisciplinary setting, including the same rheumatologists that diagnosed CTD in the RU. Results: ILD-CTD-PU patients were prevalently male and older. Progression from undifferentiated CTD to a specific condition was more common in ILD-CTD-PU, and those patients generally obtained a lower score on specific classification criteria. RA-PU patients resembled polymyalgia rheumatica in 47.6% of cases, also showing a greater proportion of typical joint deformities (p = 0.02). SSc-PU patients showed a usual interstitial pneumonia pattern in 76% of cases and, compared with SSc-RU, were more commonly seronegative (p = 0.03) and generally lacked fingertip lesions (p = 0.02). The majority of the diagnoses of pSS-PU were in patients with previously diagnosed ILD, in which seropositivity and sicca syndrome developed during follow-up. Conclusions: CTD-ILD patients diagnosed in the PU show severe lung involvement and a nuanced autoimmune clinical picture.