Clinical spectrum and profile of interstitial lung disease: an ambispective study from a tertiary center in North India

Interstitial lung diseases (ILDs) comprise a heterogeneous group of disorders characterized by varying degrees of inflammation and fibrosis, necessitating precise epidemiological characterization. This ambispective observational study evaluated the clinical spectrum and diagnostic distribution of 1201 patients at a tertiary center in North India, utilizing a multidisciplinary discussion (MDD) framework for final diagnostic consensus. The mean age of the cohort was 52.7 (±13.04) years, with a female predominance of 55.6%. Idiopathic interstitial pneumonia (IIP) was the most prevalent diagnosis (48.8%), followed by connective tissue disease-associated ILD (CTD-ILD; 19.8%) and hypersensitivity pneumonitis (14.6%). Within the IIP subgroup, idiopathic pulmonary fibrosis predominated (49.7%), followed by nonspecific interstitial pneumonia (39.2%). Statistical analysis identified tobacco use as a significant driver for IIP phenotypes (odds ratio: 3.36; 95% confidence interval: 2.37-4.75; p<0.01). Physiological assessment revealed a restrictive ventilatory defect in 83.9% of the cohort. Patients with sarcoidosis (13.4%) exhibited significantly higher functional reserve (mean forced vital capacity %: 74.1±17.9%) compared to more fibrotic subtypes (p<0.01), and demonstrated superior exercise capacity (mean 6-minute walk distance: 392.4±85.6 m vs. 347.7±90.1 m in CTD-ILD; p<0.01). These findings establish that fibrotic IIPs constitute the primary disease burden in North India, highlighting the clinical necessity of standardized, MDD-based pathways to ensure accurate phenotype differentiation and timely initiation of targeted therapies in a region characterized by complex environmental triggers.