Interstitial Lung Disease in 2025: Updated Classification, Precision Diagnostics, and Expanding Therapeutic Frontiers

Abstract

Interstitial lung disease (ILD) is an umbrella term for over 200 heterogeneous disorders that primarily affect the pulmonary interstitium and/or small airways and alveoli. These disorders are often characterized by varying degrees of inflammation and fibrosis that lead to impairment in lung function and consequent respiratory symptoms. Although idiopathic pulmonary fibrosis (IPF) remains the classic example, there exists a remarkable prevalence of cases in the context of connective tissue disease (CTD) or as a consequence of antigen exposure in the setting of hypersensitivity pneumonitis (HP). Over the past decade, the integration of high-resolution computed tomography (HRCT), extended serologic panels, increased knowledge of the natural history of disease, and the high risk of fibrotic progression across the diagnostic spectrum, has refined diagnostic certainty and allowed earlier therapeutic intervention. Contemporary guidelines from the American Thoracic Society (ATS), European Respiratory Society (ERS), and European Alliance of Associations for Rheumatology (EULAR) now emphasize pattern-based phenotyping rather than rigid disease taxonomies. Clinicians are encouraged to interpret ILD through intersecting dimensions—radiologic morphology, immune serology, and cellular aging biology—each contributing to disease trajectory and treatment response.

For Canadian respirologists, these advances coincide with a rapidly evolving therapeutic landscape (Table 1). Antifibrotic agents, selective immunomodulators, and emerging inhaled prostacyclin-based therapies are transforming the future therapeutic landscape. Yet, access to evidence-based treatments, especially for those with systemic sclerosis (SSc) and idiopathic inflammatory myopathies (IIM) related lung disease, remains inconsistent across provinces, underscoring the need for sustained advocacy. This review summarizes the 2025 classification framework, outlines novel diagnostic approaches, and appraises recent and emerging clinical trial data with practical guidance for clinical practice (Table 2).