We at Hyfe, Inc., are a company devoted to working on tools to better understand the importance of cough. It is Hyfe’s intention in the future to seek regulatory approval for medical products that analyze cough in order that they may be used to diagnose, monitor, and facilitate better treatment of respiratory illnesses.
The term interstitial lung disease (ILD) describes a group of around 200 medical conditions that cause lung damage through inflammation and scarring, impacting lung function over time.
Most symptoms of the different types of interstitial lung diseases are similar; the different types are classified based on their causes, the diagnostic test results, and how the lung disease has progressed (as seen in a lung biopsy and CT scan)12.
Many different underlying pathologies can result in ILD. These include environmental exposure, immune dysfunction, and habits such as smoking. In some cases, the underlying cause of ILD is unknown.
This article will explore the different types of ILD and how to recognize signs that may indicate you have underlying lung disease.
We categorize different types of interstitial lung disease based on their causes. There are over 200 different types of interstitial lung diseases3. The main characteristic of all the varying types of ILD is that the underlying cause results in pulmonary inflammation and eventually lung fibrosis – thickening or scarring of the lung. The types of ILD can be classified into a handful of groups, listed below.
Several autoimmune conditions can result in the development of ILD through their disease process. The premise of autoimmune diseases is that the body’s antibodies attack its own cells. This can result in ILD if the antibodies attack the lungs, although lung disease is not always a feature of autoimmune conditions. Some of the possible autoimmune causes of ILD are systemic lupus erythematosus, sarcoidosis, polymyositis, scleroderma, rheumatoid arthritis, Sjogren’s syndrome, and mixed connective tissue disease4.
Some cases of ILD result from the transfer of genetic mutations from one generation to the next. Inherited ILDs are often of two subcategories, where one category results in systemic disease affecting several different organs in the body, and the other category results in only lung disease5.
Consistent exposure to certain environmental toxins or working in industries that handle substances toxic to the lungs can result in ILD. Asbestos, silica, beryllium, cotton, and coal are common occupational exposures that cause respiratory conditions6. Respiratory disease in most of these cases results after several years of continuous exposure. Often, symptoms subside during phases of reduced exposure, which can be an indicative sign of an occupational cause for the respiratory symptoms.
It is possible to develop lung disease as a direct effect of the medicine consumption due to side-effects or toxicity resulting from the metabolites of the medicine (what the medicine is digested into). Over 350 drugs have been associated with causing interstitial lung disease, including chemotherapy drugs such as bleomycin and methotrexate, the heart drug amiodarone, and the antibiotics nitrofurantoin and daptomycin7.
Idiopathic pulmonary fibrosis (IPF) accounts for about 20% of interstitial lung disease cases8. This makes it one of the most common causes of ILD. This form of ILD is diagnosed when no other specific cause for ILD can be identified. Environmental exposure, smoking, aging, and certain genes are possible contributory factors to the development of IPF9.
The symptoms of interstitial lung disease result from the underlying fibrosis and subsequent decline in oxygen supply. Fibrosis is an excess of connective tissue in an area of the body, formed when the body over-responds to damage.
Approximately 50–98% of patients with ILD present with cough and breathlessness as their primary symptoms10. These symptoms may only present much later in the disease process, which means it is possible to have no symptoms for a significant time with ILD. If autoimmune conditions are causing ILD, they will also present with classic signs of the autoimmune disease.
Some other possible signs associated with ILD include:
Patients also report anxiety and depression due to a decrease in the quality of life related to symptoms of ILD11. Sleep-related breathing concerns have also been frequently noted among patients with ILD12.
Those who present with occupational ILD may report a decrease in their symptoms during periods of limited exposure.
While the causes mentioned above are directly linked to interstitial lung disease, there are some factors that, when exposed to, can increase your chances of developing ILD.
Some of these risk factors include working in industries that increase your exposure to pulmonary toxins (substances damaging to the lungs), undergoing chemotherapy, or taking other forms of pulmonary–toxic medications. Exposure of the lungs to radiation also increases the risk of ILD13. The chances of developing ILD increases following radiation, if someone has more than one risk factor.
Among lifestyle factors, smoking is a risk factor that contributes significantly to the likelihood of developing ILD, as tobacco contains various pulmonary toxins. Coupling smoking with an autoimmune condition, or ILD-related gene mutations can increase this risk further, which makes quitting the habit the best way to reduce your overall risk.
Age is also a risk factor for ILD; while ILD can be recorded at any age, certain variants, such as idiopathic pulmonary fibrosis, are commonly noted among older individuals14.
Patients who have a history of lung infections are also more likely to develop interstitial lung disease. While individual incidents of infections may not be linked, repeated infections, especially among those who have other risk factors, can contribute as a long-term risk factor for ILD15.
Once the disease process has resulted in fibrosis it is not usually possible to reverse the existing fibrosis. However, if ILD is promptly identified it is possible to slow the progression of the disease and tackle the underlying inflammation.
For the cases of ILD where a known underlying cause has been observed, such as medications or occupational exposure, avoiding the pulmonary toxin is the first step in management. Additionally, certain lifestyle measures, such as quitting smoking, regular exercise to improve lung capacity, and avoidance of air pollutants can also help slow down the disease process.
There are a few standard measures used to manage interstitial lung disease. Supplemental oxygen is one such measure that is considered for almost all cases, especially those who have low oxygen saturation. Pulmonary rehabilitation – a collection of exercises and a program of education – is regularly conducted for patients of ILD to improve lung function and build tolerance for strenuous activities. Finally, different breathing techniques help to improve lung function.
If a disease progresses even after limiting exposure, we use corticosteroids to moderate underlying inflammation. While corticosteroids can be useful in different capacities for the differing variants of ILD, patients with certain types of ILD see immediate results from the administration of steroids, particularly hypersensitivity pneumonitis16 and cryptogenic organizing pneumonia (COP), formerly known as bronchiolitis obliterans organizing pneumonia (BOOP)17..
Similarly, in cases of sudden worsening of ILD symptoms and the underlying inflammation, steroids are proven to be beneficial in improving symptoms and disease progress18.
Many studies have supported the concurrent use of immunosuppressants with steroids for improving ILD disease outcomes. Azathioprine and mycophenolate mofetil are some of the primary drugs used along with initial steroid therapy to manage the immune system19. These drugs are also called immunomodulators. This standard regime is the first-line therapy for idiopathic pulmonary fibrosis.
Based on how the patient responds to therapy, immunomodulators can be used as a stand-alone treatment to mitigate the long-term effects of steroid therapy.
Antifibrotic therapy has been studied for its benefits for both slowing down ILD progress and improving lung function. Currently, two antifibrotic drugs, nintedanib and pirfenidone, have been approved by the FDA for use in IPF20. There is a third antifibrotic drug entering trials21 – AGMB-129 – although this is currently only marked for a certain type of Crohn’s disease22.
While varying combinations of therapeutic approaches can be considered for patients who present with ILD, most only slow down disease progress rather than stop it. Therefore, lung transplantation is the definitive treatment strategy for patients with ILD23.
Complications in ILD arise as a consequence of a decline in lung function.
As fibrosis progresses, there is less gas exchange taking place within the healthy lung tissues, which results in decreased oxygen supply.
Additionally, diseased lungs are more susceptible to infections. Respiratory infections can worsen underlying lung conditions, and as a consequence can also contribute to the development of further infections. Studies have also shown that, despite their use as a treatment, the use of immunosuppressants in ILD or related autoimmune conditions is associated with an increased risk of developing additional pulmonary infections24.
ILD has also been linked to complications such as cardiac disease25 and pulmonary hypertension26. Fibrosed lungs are also susceptible to the development of life-threatening pulmonary thromboembolism27, a blockage of an artery in the lungs.
Diseased lungs are susceptible to lung cancer as a complication as well. A review of medical literature documented an 18–20% estimated occurrence of lung cancer among patients with ILD. More than 15% of these patients are also likely to die from lung cancer and its complications28.
If underlying genes or autoimmune conditions are the cause resulting in ILD, then ultimately there are limited management options that can halt the progress of lung fibrosis and ILD.
Modifiable risk factors such as smoking, lifestyle habits, and occupational exposure can be altered to lower the overall risk of developing ILD. Prompt diagnosis and management during early presentation (for instance, in drug-induced ILD) can help slow down disease progress and prevent severe complications of ILD.
Interstitial lung disease is the name of a group of pulmonary disorders that result in fibrotic changes within the lung. Over time as the disease progresses, lung function declines, limiting oxygen supply. Autoimmune conditions, genetic mutations, occupational exposure, and specific drugs are possible contributory factors to the development of ILD. Difficulty breathing and a persistent cough are frequently the only signs of underlying lung disease. The progression of symptoms should prompt medical attention and subsequent diagnosis. Treatment is often with a combination of supportive care and standard medications. Lung transplantation is usually the definitive way to permanently defeat interstitial lung disease.References
Michelle is a healthcare consultant and content creator with over six years of experience in the FemTech space. She contributes extensively to health forums, especially those centered on enabling wellness, advancing digital health, and FemTech solutions. She loves classic rock music, reading classic literature, and finding new spots in town for good food and some chai.