Progressive Pulmonary Fibrosis

Idiopathic Pulmonary Fibrosis

Jeremy Feldman, MD

Interstitial Lung Disease and Progressive Pulmonary Fibrosis

By

Disorders characterized by inflammation or scarring in the lungs may be the most complicated area within lung medicine.  Not only are the names confusing but they have repeatedly changed over the past 50 years.  Furthermore, many of the early studies describing the natural history of one disease or another have turned out to be inaccurate.  To make matters worse, it was not until 2015 that the first effective therapy was approved.  

The alphabet soup of interstitial lung diseases

Interstitial lung diseases are a collection of lung disorders characterized by inflammation, scarring or structural changes to the supporting tissues of the lung.  Over time, many of these disorders lead to impairment in the ability of the lungs to move oxygen into the blood. In the past, we relied heavily on lung biopsy and what the lungs looked like under a microscope in order to make a specific diagnosis.  More recently, the field has moved towards a focus more on high resolution CT scanning. 

Within the large family of interstitial lung diseases (ILD), there are many specific entities.  Below is a list of some of the more commonly encountered diseases. 

  1. Idiopathic pulmonary fibrosis (IPF):  the best known ILD.  This is a disease of older people (> 50 and often over 60).  It is characterized by progressive replacement of the lung with scar.  Patients often have cough and eventually all develop shortness of breath.  Without treatment this disease progresses and leads to death.  
  2. Non-Specific interstitial pneumonitis (NSIP):  this ILD comes in two flavors—cellular (which has a better prognosis) and fibrotic (which behaves more like idiopathic pulmonary fibrosis).  Fibrotic NSIP can be a challenge to separate from IPF based on CT scanning.  
  3. Hypersensitivity Pneumonitis (HP):  this ILD is felt to result from ongoing exposure to something in the environment that triggers an off-target immune response that leads to lung inflammation.  Common triggers include birds and mold.  Some patients develop HP yet no specific environmental trigger can be found.  The CT scan characteristics often allow this diagnosis to be made confidently without a lung biopsy. 
  4. Connective tissue disease associated ILD (CT-ILD):  rheumatoid arthritis and scleroderma in particular can have lung involvement. 
  5. Respiratory bronchiolitis with Interstitial lung disease (RB-ILD):  a disease of smokers.  Often found on CT imaging but may not have prominent symptoms
  6. Desquamative Interstitial Pneumonitis (DIP):  almost exclusively seen in smokers.  Often improves in response to quitting smoking. 
  7. Sarcoidosis:  This multi-system disease can affect any part of the body.  The lungs are most commonly affected.  Patients can have enlarged lymph nodes, scarring and airway abnormalities.  
  8. Pulmonary Langerhans cell histiocytosis  (PLCH):  this can be a lung limited disorder or involve the brain, bones and other organs.  Most commonly seen in smokers. 

Some interstitial lung diseases are progressive over time and others may be stable for years.  In order to label an interstitial lung disease as progressive it must meet at least one of the following criteria:

  1. Decline in forced vital capacity (FVC) by 5% in 6 month or 10% in two years
  2. 5-10% decline in FVC and worsening fibrosis on CT scan or increased shortness of breath
  3. Worsening fibrosis on CT and progressive symptoms. 
  4. 15% decline in the diffusing capacity

It is important to identify progression as this has a big impact on your prognosis.  In order to determine if your disease is progressing, you need periodic measurements of your lung function (pulmonary function testing) and chest imaging (CT chest). If your disease is progressing you should talk to your doctor about intensifying your treatment.  For patients not taking any antifibrotic medication this should prompt you to consider taking antifibrotic therapy.  If you are progressing despite being on antifibrotic therapy, then you should discuss participating in a clinical trial with your doctor or changing your regimen. 

There are many drugs being studied for progressive pulmonary fibrosis and the future is bright.  I remain optimistic that over the next few years we will see new medications approved that will help slow the progression of fibrotic lung disease.