Understanding ILD

Interstitial Lung Disease refers to a large group of lung disorders that cause inflammation or scarring in the lung tissue.

The term “interstitial” refers to the area that surrounds the airsacs (alveoli) of the lung. This interstitial space is where the oxygen that you breathe in moves across the wall of the alveoli and into the small blood vessels (capillaries) that cover the airsacs. Once the oxygen crosses this alveolar-capillary membrane into the blood stream, it is delivered to your brain, muscles, kidneys, and other vital organs. The interstitial space around the alveoli can become inflamed, thickened or scarred because of a variety of insults, exposures, or reactions in the lungs.

What causes ILDs?

There are many causes of ILDs and they can be categorized in many different ways. The groups pictured above is one way to organize three main into three broad groups:

  1. Exposure-Related 
  2. Autoimmune-Related
  3. Idiopathic, or with no known cause.

These three groups of ILDs have slightly different presentations, and different findings on the CT scans, lung tissue biopsy (if done), and bloodwork results. Each group also has different treatment choices which is why getting a correct diagnosis is extremely important.

Exposure-Related (Hypersensitivity Pneumonitis or 'HP'):

  • Inhalation-related:
    • There are more than 300 causes of inhalational exposure-related ILDs.
    • These exposures can be experienced in the workplace, at home, while doing hobbies, or during travel.
    • It is estimated that over 50% of the time the specific exposure is never identified. An "HP Panel" can be ordered to identify whether or not you have been exposed to certain "antigens", such as birds.  However, even if this testing documents that you have developed antibodies for a particular antigen, it does not necessarily mean that is the definite cause of your HP.
    • When being evaluated for exposure-related ILDs, your physician may ask you to complete an “Exposure History” questionnaire and will also ask you many questions about your history to see if there may be risk factors that we can identify. Some of the more common exposures are mold, birds in or around the home, bedroom, or backyard, farming/agricultural work, indoor hot tubs, standing water, down feathers, and cleaning chemicals.
    • Historically, coal miners (pneumoconiosis) and exposure to asbestos (asbestosis) were significant problems, but these exposures have lessened due to the use of protective respiratory equipment.
    • Having any of the above exposures does not necessarily mean that you will develop a lung problem. For reasons that are not completely understood, some persons are at increased risk of having a lung reaction to exposures than others.
    • If you undergo a lung biopsy, the pathologist can confirm a diagnsosi of  Hypersensitivity Pneumonitis by  findings in the lung tissue.

  • Medication-related:
    • While ILDs due to a medication are less common than inhalation-related ILDs, they do occur.
    • Just like the inhaled exposures, it is important for your physician to obtain a detailed medication history during your ILD evaluation, especially as it relates to timing of the medication with changes in your lung symptoms.
    • Some of the medications that can cause an inflammatory reaction in the lung include amiodarone, methotrexate, some chemotherapy agents used to treat cancers, and nitrofurantoin (sulfa drugs).
    • Radiation-Exposure related: Some people have had radiation exposure in their chest area, such as with breast cancer treatment. Radiation-induced lung scarring is another cause of ILD.

Autoimmune-Related ILDs (Nonspecific Interstitial Pneumonitis – NSIP):

  • Autoimmune refers to your body having some type of inflammatory reaction that results in the development of antibodies that are detected with a blood test. Some types of autoimmune disease can cause inflammation and scarring in the lung. The pattern on the CT scan most often seen with autoimmune-related ILDs is non-specific interstitial pneumonitis; this description can also be used when describing a lung tissue biopsy sample by the pathologist.
  • Many autoimmune diseases are associated with physical signs such as rashes, changes in the skin and hands, inflammation of joints, muscle soreness or weakness, and dry eyes and mouth.
  • Autoimmune–related ILDs tend to occur more often in women and in persons under the age of 65.
  • Examples of autoimmune diseases are rheumatoid arthritis, dermatomyositis, polymyositis, Sjogrens Syndrome, Scleroderma, and vasculitis.
  • A diagnosis of an autoimmune disease is made by blood tests known as 'serology' that detect and measure the level of certain antibodies in the blood. 
  • In some patients, a diagnosis of an autoimmune disease is made first, and then a few years later the autoimmune lung disease manifests itself as an ILD. In other patients, the ILD lung problem may occur first and then a few years later the autoimmune disease may develop with changes in the skin, joints,  and positive serology.

Idiopathic ILDs (no known cause):

  • Idiopathic Pulmonary Fibrosis (IPF) is the most common ILD that has no known cause.
  • IPF is also referred to as Usual Interstitial Pneumonia or UIP.  UIP describes the particular pattern seen on the CT scan, and can also be used by the pathologist to describe the lung tissue findings if a lung biopsy was done.
  • The diagnosis of UIP is made by determining if the pattern on the CT scan is either definitive or possible for UIP, and by eliminating other causes of ILD such as autoimmune disease or an exposure.  
  • There is research identifying specific ‘biomarkers’ of IPF that occasionally (<20%) occur in families (familial IPF), but the cause of IPF is poorly understood. It more commonly occurs in men, ex-smokers, and usually occurs between the ages of 60 and 80. There are now some blood tests available to check for genetic causes of IPF and ILDs.
  • In 2014 two new anti-fibrotic drugs were approved for the treatment of IPF Ofev (nintedanib) and Esbriet (pirfenidone). Both of these medications slow the progression of IPF, but do not stop the process or remove the existing scar tissue.
  • Other Idiopathic ILDs: Other ILDs with no known cause include some cases of non-specific interstitial pneumonitis (NSIP), cryptogenic organizing pneumonia (COP), and Sarcoidosis. In some cases the cause of the ILD may be unknown or 'indeterminate' in which case a patient might undergo a surgical lung biopsy, or a transbronchial biopsy with bronchoalveolar lavage in order to get additional information to make a diagnosis.