Is Idiopathic Pulmonary Fibrosis an Interstitial Lung Disease?
Yes, idiopathic pulmonary fibrosis (IPF) is definitively a type of interstitial lung disease (ILD)—specifically, it is one of several idiopathic interstitial pneumonias and represents the most common and severe form of ILD. 1
Classification and Definition
IPF is classified as one of the idiopathic interstitial pneumonias (IIPs), which collectively fall under the broader umbrella term of interstitial lung diseases (ILDs) or diffuse parenchymal lung diseases. 1
IPF is defined as a specific form of chronic, progressively fibrosing IIP that occurs primarily in relatively elderly adults and is associated with the histopathological pattern of usual interstitial pneumonia (UIP). 1
IPF is the most pernicious and frequent of the ILDs, accounting for 55% of all idiopathic interstitial pneumonias. 1
Distinguishing IPF Within the ILD Spectrum
IPF is now recognized as a distinct clinical disorder within the ILD family, characterized by progressive lung scarring and the histological picture of usual interstitial pneumonia. 1, 2
The 2022 ATS/ERS/JRS/ALAT guidelines explicitly distinguish IPF from other ILDs when discussing progressive pulmonary fibrosis (PPF), noting that IPF is excluded from the definition of PPF because virtually all IPF patients will manifest disease progression. 1
Other ILDs that can be confused with IPF include fibrotic nonspecific interstitial pneumonia (NSIP), connective tissue disease-associated ILD (particularly rheumatoid arthritis), chronic hypersensitivity pneumonitis, cryptogenic organizing pneumonia, and various exposure-related ILDs. 3, 4
Clinical Significance of This Classification
Understanding that IPF is a specific type of ILD is critical because IPF carries a significantly worse prognosis than other histological patterns of chronic interstitial pneumonia, with an estimated 5-year survival rate worse than several types of cancer. 1
The distinction matters for treatment: antifibrotic therapy (pirfenidone and nintedanib) is specifically indicated for IPF, while other ILDs may require different therapeutic approaches unless they develop progressive pulmonary fibrosis. 1, 5, 6
IPF affects approximately 3 million people worldwide, with incidence increasing dramatically with age, making it a substantial public health concern within the broader ILD category. 1, 2