Role of High-Resolution CT Thorax in Diagnosing Interstitial Lung Disease and Its Association With Smoking and Connective Tissue Disorder

Introduction Interstitial lung diseases (ILDs) primarily affect the interstitium, an alveolar wall tissue between the capillary endothelium and the alveolar epithelium. The term ‘interstitial,’ however, is misleading since alveolar spaces, peripheral airways, and vessels can be involved in most of these disorders.They often require a multidisciplinary diagnosis i.e., an integration of clinical, radiological, and pathological findings. A chest radiograph is relatively insensitive because of nonspecific patterns. Generally, these disorders can progress to irreversible pulmonary fibrosis and are an important cause of morbidity and mortality. It is critical to make a prompt and accurate diagnosis of the underlying causes so that patients can be managed appropriately. ILD is subdivided into idiopathic interstitial pneumonia, of which idiopathic pulmonary fibrosis (IPF) is one subset, and diffuse parenchymal lung diseases, which may be secondary to a variety of occupational or environmental exposures or others. They can complicate multiple rheumatic or connective tissue diseases (CTDs). Apart from ILD, other forms of lung damage involving the pleura, vasculature, airways, and lymphatic tissue can complicate CTDs. Aims Aims include studying the role of high-resolution computed tomography (HRCT) in diagnosing various ILDs based on morphologic patterns, evaluating the correlation between ILD and various connective tissue disorders and the prevalence of complications in such patients, and evaluating the association of smoking with various ILDs. Methods This is a retrospective study in which HRCT thorax was performed on a 128-slice Philips CT scanner machine on 50 patients from December 2020 to February 2022 in SVP Hospital, Ahmedabad. No age or gender bias was followed. Result Out of 50 patients studied, 19 (38%) patients had the usual interstitial pneumonia (UIP) pattern and 12 (24%) had the nonspecific interstitial pneumonia (NSIP) pattern. These two were the most common among all ILD patterns. Other patterns found were hypersensitivity pneumonitis (5; 10%), respiratory bronchiolitis-related ILD (3;6%), and organizing pneumonia (2; 4%). In nine patients, the morphologic pattern was either subtle (3; 6%) or mixed (6; 12%), and the final diagnosis remained inconclusive; patients were advised clinical correlation and biopsy. Eleven (22%) patients had a history of smoking. Among smokers, the most common pattern was UIP while all patients with respiratory bronchiolitis (RB) ILD had a history of smoking. Fourteen (28%) patients showed a positive association with CTD. Among them, rheumatoid arthritis (RA) was the most common CTD and the most common pattern among RA patients was UIP. Ten (20%) of patients developed pulmonary arterial hypertension, of which two patients who had connective tissue disorder developed pulmonary arterial hypertension at a young age (24 years). The rest of the patients who developed pulmonary arterial hypertension were above 45 years of age. Among these, two were smokers. Conclusion HRCT plays an important role in the diagnosis of ILD on the basis of various morphological patterns. CTD plays a significant role in the development of ILD. UIP is the most common ILD among patients with a smoking history and RA. NSIP Is the most common in patients with CTD other than RA. Pulmonary arterial hypertension (PAH) develops early in patients with CTD. There is a significant risk of the development of PAH in patients with chronic ILD.