Interstitial lung disease (ILD), is actually a group of more than 100 different lung diseases that currently affect about 400,000 people in the US.

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Your lungs are always hard at work. Those two spongy, air-filled organs on either side of our breastbone are constantly taking in fresh air, and removing waste gases (e.g., carbon dioxide) from your body. When your lungs are working as they should, it's easy to forget just how important they are to your body's functioning—but at the first instance of a dry cough or difficulty taking in air, it's hard to ignore their importance.

Those two symptoms—dry cough and shortness of breath—are two of the most common symptoms of something called interstitial lung disease, a condition (technically a group of diseases) that about 400,000 people in the US are currently dealing with, according to the American College of Chest Physicians' Chest Foundation. That's a large number—primarily because interstitial lung disease (ILD) includes more than 100 specific diseases. Overall, it's estimated that ILD accounts for about 15% of cases seen by pulmonologists (aka lung doctors), per National Jewish Health.

ILD can often be difficult to diagnose; according to the Chest Foundation, because symptoms of ILD are so often similar to other lung conditions, half of all cases are initially misdiagnosed. Here, pulmonologists explain what you need to know about ILD, including the most common symptoms and causes, as well as how physicians typically treat the condition.

What exactly is interstitial lung disease?

Interstitial lung disease, at its core, is a group of lung diseases that cause lung inflammation and/or scarring (aka fibrosis), according to the Chest Foundation. While sometimes ILD is referred to as interstitial pneumonia, that's not entirely correct. For the most part, typical pneumonia is inflammation in the lungs due to infection, but "interstitial lung disease is a broad category of lung diseases that cause inflammation in the lung tissue in the absence of infection," Thomas Monaco, MD, assistant professor of pulmonary medicine at Baylor College of Medicine, tells Health.

The inflammation and scarring in ILD occurs in the interstitium, or a collection of support tissues, in the lung, Reynold A. Panettieri, Jr., MD, professor of medicine at Rutgers Robert Wood Johnson Medical School and director of the Rutgers Institute for Translational Medicine & Science, tells Health. According to the Chest Foundation, this scarring happens happens gradually; the inflammation in the lungs leads to scarring, which then leads to the alveoli (the lungs' tiny air pockets) to become thickened and stiff. "The scarring can be quite substantial and cause loss of lung function," says Dr. Panettieri.

Because there are so many different types of ILD, doctors usually separate them into groups. Here are some of the most common subtypes, according to the Chest Foundation:

  • Pneumoconioses: This group of ILDs are caused by inhaling certain dusts, according to the Centers for Disease Control and Prevention (CDC). This is typically caused by occupational or work-place exposure.
  • Granulomatous: A granuloma is technically a small area of inflammation, according to the Mayo Clinic. In this type of ILD, granulomas are found in the lungs.
  • Collagen vascular disease: This type of ILD can occur when someone has an autoimmune disease, in which their immune system mistakenly attacks its own body.
  • Drug toxicity: These ILDs are typically caused by drugs including chemotherapy and methotrexate, among others.
  • Rare causes: According to the Chest Foundation, these types of ILDs are extremely rare and "have special features that distinguish them from other ILDs."
  • Idiopathic and rare idiopathic ILD: There's no known cause for these ILDs, which include acute interstitial pneumonia (AIP), lymphoid interstitial pneumonia (LIP), and cryptogenic organizing pneumonia (COP).
  • Chronic fibrosing: The Chest Foundation says these types of ILDs take quite a while to develop and cause symptoms—and, when detected, are usually irreversible.
  • Smoking-related ILD: Though smoking can rarely cause ILD, it can still happen—and in that case, the first step to treatment is to stop smoking.

What causes interstitial lung disease?

Because there are so many types of ILD, there are also quite a few different potential causes. "Many different things can cause interstitial lung disease, and we are learning about more causes all the time," says Dr. Monaco.

According to National Jewish Health, there are four main causes of ILD:

  • Autoimmune or connective tissue diseases: According to Dr. Monaco, having a preexisting autoimmune condition (think: lupus, rheumatoid arthritis, inflammatory bowel disease) can raise your risk of ILD.
  • Exposure to an agent that can damage the lungs: This can happen in an occupational environment, like when someone is exposed to asbestos or coal dust, Shweta Sood, MD, MS, a pulmonologist at Penn Medicine, tells Health. But it can also include instances of smoking, or using certain medications.
  • Genetics: "Some interstitial lung diseases are inherited and passed down from one generation to the next," Dr. Monaco says. Those can include diseases like neurofibromatosis and Gaucher disease.
  • Idiopathic: These are essentially unknown causes for ILD. The types associated with this cause include: sarcoidosis, idiopathic pulmonary fibrosis, and acute interstitial pneumonia, among others.

What are the symptoms of interstitial lung disease?

This relates to the many different types of ILD, as well—the symptoms are usually quite nonspecific. "The symptoms of interstitial lung disease are challenging because they're vague," says. Dr. Sood. That, again, is why many cases of ILD are often misdiagnosed at first. Many patients have even reported going without a diagnosis for more than a year after the onset of symptoms, according to the Chest Foundation.

According to Dr. Sood, "the uniform feature is some sort of lung scarring that can make it hard to breathe." Though every person is different, these are the most common symptoms reported with ILD in general, according to Stanford Health Care:

  • Shortness of breath or trouble breathing
  • Dry cough
  • Fatigue and weakness
  • Loss of appetite
  • Unexpected weight loss
  • Chest pain or discomfort
  • Bleeding in the lungs

How is interstitial lung disease diagnosed and treated?

Like with any diagnosis, your doctor will first take stock of your own personal medical history as well as your family's. You'll also have a complete physical exam, and possibly a high-resolution computed tomography (CT) scan, Jewish National Health says.

Past that, more tests that your doctor may want to perform include: certain blood tests, lung function tests, imaging tests, and tissue sampling tests, per the Chest Foundation.

As far as treatment goes, "you have to treat the underlying cause," says Dr. Panettieri. If someone is experiencing ILD from another autoimmune condition, corticosteroids or immunosuppressive medications can help tamp down the body's immune response, he says. If a person developed ILD from exposure, however, there's a chance the "lung disease will resolve and the lungs will begin to heal as soon as the offending substance is removed," says Dr. Monaco.

There are also medications called anti-fibrotics that interrupt the process of scars forming and "significantly slow" the process of replacing lung tissue with scarring over time, Dr. Monaco says—but those are nly Ultimately, "the treatments are almost as varied as the causes of interstitial lung disease," he adds.

Other therapies that don't involve medical intervention include pulmonary rehabilitation, oxygen therapy, or even lung transplantation ("[ILD is] one of the most common reasons why people get lung transplants these days," says Dr. Sood).

If you or someone you know has ILD, it's also important to take stock of your current wellness routine and make changes accordingly—that means quitting smoking, focusing on maintaining a healthy lifestyle, keeping up with medications, and protecting yourself against the flu, COVID-19, or other respiratory diseases through proper hygiene, mask-wearing, and vaccination.

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