Causes of Interstitial Lung Disease

Primary Etiologic Categories

Interstitial lung diseases can be classified into three major etiologic categories: those associated with underlying systemic disorders, those caused by antigenic or toxic exposures, and idiopathic disorders without identifiable cause, according to the American College of Chest Physicians 1
Connective Tissue Disease-Associated ILD (CTD-ILD) accounts for approximately 20% of all ILDs, as stated by the European League Against Rheumatism 2
Systemic sclerosis (SSc-ILD) accounts for approximately 31% of CTD-ILDs, and Rheumatoid arthritis (RA-ILD) accounts for approximately 39% of CTD-ILDs, according to the European League Against Rheumatism 2
Sjögren's syndrome causes autoimmune-mediated lymphocytic infiltration of lung parenchyma, as reported by the American College of Rheumatology 3

A detailed exposure history is mandatory, as 47% of patients presenting with apparently idiopathic ILD may actually have hypersensitivity pneumonitis when thoroughly evaluated, according to the American Thoracic Society 4
Occupational exposures to metal, silica, and environmental tobacco smoke increase IPF risk with a pooled odds ratio of 1.7 (95% CI 1.42-2.03), as reported by the National Institute for Occupational Safety and Health 4

The American Thoracic Society emphasizes that systematically excluding medication history, environmental exposures, connective tissue disease, and occupational exposures is mandatory because identification and removal of causative factors may result in improved clinical outcomes 4
The American College of Chest Physicians recommends a comprehensive review of all current and recent drugs to exclude medication-induced ILD 4

The American Thoracic Society warns that failing to obtain a sufficiently detailed exposure history is a critical error, as nearly half of patients initially thought to have idiopathic disease actually have hypersensitivity pneumonitis when properly evaluated 4
The European Respiratory Society advises against relying solely on patient recall and recommends using standardized questionnaires tailored to cultural habits and geographical differences 4
The American College of Rheumatology suggests considering drug-induced ILD in any patient with CTD-ILD who progresses despite appropriate therapy, as the medications used to treat the underlying CTD can themselves cause ILD 3