Interstitial Lung Disease

Overview

The information on these webpages is intended as an educational resource for health professionals, including those working in primary care and respiratory specialists. The information has been developed by health professionals from the Centre of Research Excellence in Pulmonary Fibrosis. It is a general guide and does not replace specialist knowledge or individualised patient care. 

Interstitial Lung Diseases (ILDs) are a complex group of more than 200 diseases characterised by some degree of fibrosis and/or inflammation of the lung interstitium. This may result in physiological impairment, causing significant morbidity and mortality. There is a wide spectrum of ILD, and heterogeneity of disease course, with some patients having stable disease, and others progressing very quickly to respiratory failure and death.   

While individual ILDs may be considered rare, as a group, prevalence is estimated at around 70-100 per 100,000, and this is increasing year by year. 

Interstitial lung disease (ILD) or pulmonary fibrosis (PF)? 

ILD is the clinically appropriate term for this group of diseases. Pulmonary fibrosis (PF) is a commonly used umbrella term for the large proportion of ILD’s which are characterised by fibrosis or scarring in the lung parenchyma. Note that we use the term PF in all resources and content developed for patients as the better lay term and more commonly understood name for the group of conditions. 

Types of ILD 

ILD may be idiopathic (otherwise known as the group of idiopathic interstitial pneumonias), or associated with exposure to drugs or environmental triggers, or underlying connective tissue disease.  Types and classification of ILDs are summarised in the table below. More is now known about genetic causes of ILD.  While this is rare, ILD may be familial, and can be associated with short telomere syndromes which also can have other clinical manifestations.  Referral to an ILD specialist centre with genetic testing is advisable in younger patients or patients with a family history of ILD or extrapulmonary features of telomeropathies.   

Types and classification of the most common Interstitial Lung Diseases (ILDs)

ILDs of known association 

• Connective tissue disease 
• Drugs (e.g. nitrofurantoin) 
• Occupational exposures 

Granulomatous ILDs 

• Sarcoidosis 
• Hypersensitivity pneumonitis 

Idiopathic interstitial pneumonias (IIPs) 

• Major IIPs:
  • Idiopathic pulmonary fibrosis (IPF) 
  • Non-specific interstitial pneumonia 
  • Cryptogenic organising pneumonia 
  • Respiratory bronchiolitis ILD 
  • Desquamative interstitial pneumonia 
  • Acute interstitial pneumonia 

• Rare IIPs 
  • Lymphocytic interstitial pneumonia 
  • Idiopathic pleuro-parenchymal fibroelastosis  

• Unclassifiable 

Miscellaneous ILDs 

• Lymphangioleiomyomatosis (LAM) 
• Pulmonary Langerhans cell histiocytosis (histiocytosis X) 

Idiopathic pulmonary fibrosis (IPF) is the most common of the idiopathic interstitial pneumonias, and has the highest mortality, with a mean survival of 2-5yrs from diagnosis.  Much of the literature and evidence base is focused on IPF. 

In the last few years, there has been a shift towards grouping patients with progressive disease together despite the aetiology of the condition.  The term Progressive Pulmonary Fibrosis (PPF) has been coined to describe those patients without IPF who have progressive disease despite optimal treatment.   

Helpful links  

• Connective Tissue-Related Interstitial Lung Disease Primer (2020) 
• Contemporary Concise Review 2023: Interstitial lung disease 
•  IPF Primer (2019) 
•  Progressive Fibrosing Interstitial Lung Disease Primer (2020) 
• Treatment of idiopathic pulmonary fibrosis and progressive pulmonary fibrosis: A position statement from the Thoracic Society of Australia and New Zealand 2023 revision  
• Connective Tissue-Related Interstitial Lung Disease Primer (2020) 
• Contemporary Concise Review 2023: Interstitial lung disease 
•  IPF Primer (2019) 
•  Progressive Fibrosing Interstitial Lung Disease Primer (2020) 
• Treatment of idiopathic pulmonary fibrosis and progressive pulmonary fibrosis: A position statement from the Thoracic Society of Australia and New Zealand 2023 revision  

References

• “Diagnosis of Idiopathic Pulmonary Fibrosis. An Official ATS/ERS/JRS/ALAT Clinical Practice Guideline.”  
• “Idiopathic Pulmonary Fibrosis.”  
•  “The interstitial lung disease multidisciplinary meeting: A position statement from the Thoracic Society of Australia and New Zealand and the Lung Foundation Australia.” 
• “The natural history of progressive fibrosing interstitial lung diseases”. 
• “What’s in a name? That which we call IPF, by any other name would act the same.”  
• “Diagnostic criteria for idiopathic pulmonary fibrosis: a Fleischner Society White Paper.”  
• “Diagnosis of Idiopathic Pulmonary Fibrosis. An Official ATS/ERS/JRS/ALAT Clinical Practice Guideline.”  
• “Idiopathic Pulmonary Fibrosis.”  
•  “The interstitial lung disease multidisciplinary meeting: A position statement from the Thoracic Society of Australia and New Zealand and the Lung Foundation Australia.” 
• “The natural history of progressive fibrosing interstitial lung diseases”. 
• “What’s in a name? That which we call IPF, by any other name would act the same.”