What you need to know about interstitial lung disease (ILD)

Interstitial lung disease (ILD) refers to a group of over 200 conditions that cause damage to the lungs, often leading to breathlessness, a dry cough and fatigue. While ILD can be a serious condition, early diagnosis, expert care and advances in treatment can make a real difference.  

In this article, we will explore what happens in ILD, its common causes and symptoms, how it is diagnosed, and how it can be treated and managed. 

What goes wrong in ILD?

In healthy lungs, oxygen passes easily from tiny air sacs called alveoli into the bloodstream, allowing the body to get the oxygen it needs. In ILD, the delicate tissue around the air sacs, which is called the interstitium, becomes thickened, scarred (fibrosis) or inflamed, depending on the underlying cause. 

In some types of ILD, such as idiopathic pulmonary fibrosis (IPF), progressive scarring (fibrosis) occurs without much inflammation. In other types, such as ILD linked to autoimmune diseases, inflammation plays a more active early role, which may sometimes be reversible with the correct treatment. 

As the interstitium becomes thicker and stiffer, the lungs become less able to expand and contract, and it becomes harder for oxygen to move into the blood. This can lead to symptoms like breathlessness, a persistent cough and fatigue. 

Early on, these symptoms might only be noticeable during exercise, but they often worsen over time. In more advanced stages, low oxygen levels can affect daily activities and overall health.

Early diagnosis and specialist care are crucial to slowing disease progression, managing symptoms and maintaining the best possible quality of life.

Causes of ILD

There are many different causes and types of ILD, although sometimes no clear cause can be found. 

The most common type is idiopathic pulmonary fibrosis (IPF), where lung scarring develops without an identifiable trigger. IPF tends to affect people over the age of 50 and occurs more often in those with a family history of the disease. Of the roughly 150,000 people living with ILD in the UK, around 30,000 have IPF.

Other causes of ILD include: 

• Autoimmune conditions eg rheumatoid arthritis, systemic sclerosis and myositis 
• Occupational and environmental exposures such as inhaling asbestos, silica dust, coal dust or agricultural chemicals 
• Medications including certain antibiotics, chemotherapy drugs and antiarrhythmic medications
• Hypersensitivity pneumonitis — this refers to an allergic reaction to inhaled organic particles like moulds, bird droppings or farm dust

In a significant proportion of cases, particularly in older adults, ILD remains idiopathic, which means no clear cause is found despite a thorough investigation. 

Symptoms of ILD

Symptoms of ILD can develop gradually and are often mistaken for other conditions, particularly in the early stages. Common symptoms include:

• A persistent dry cough
• Breathlessness, initially with exertion and later even at rest
• Fatigue and reduced energy levels
• Unexplained weight loss 

However, these symptoms are often very subtle in the early stages and can, therefore, be misattributed to ageing, asthma, COPD or heart disease. This can potentially delay diagnosis. 

Getting a diagnosis of ILD

If ILD is suspected, early and accurate diagnosis is essential to guide appropriate treatment. The diagnostic process typically begins with your GP, who will:

• Ask detailed questions about your symptoms, exposures, hobbies, medications and underlying health conditions
• Listen to your chest for distinctive sounds called “crackles”, which are heard with a stethoscope

If your GP suspects ILD, they may refer you to a respiratory specialist for further investigations, including:

• A chest CT scan to identify patterns of scarring, inflammation or other lung abnormalities
• Pulmonary function tests, which can include spirometry and gas transfer
• Blood tests to screen for autoimmune diseases or other markers associated with ILD
• Bronchoscopy or a lung biopsy — these are rarely needed but may be performed if the diagnosis remains uncertain after initial tests

Diagnosis is often confirmed through a multidisciplinary team (MDT) approach, involving several specialist doctors, including respiratory physicians, radiologists and sometimes pathologists. This helps to ensure the most accurate diagnosis. 

Treating ILD

While there is no cure for most forms of ILD, treatment aims to slow disease progression, control symptoms and maintain quality of life. 

Treatment strategies may include:

• Removing triggers — if exposure to a harmful substance is identified, avoiding the exposure is critical
• Treating underlying causes — If ILD is associated with an underlying autoimmune condition, immunosuppressive medications may be prescribed
• Antifibrotic therapies — in IPF and other ILDs that involve scarring (fibrosis), medications such as nintedanib and pirfenidone can slow down the rate of lung scarring but cannot reverse existing damage
• Supportive therapies such as home oxygen, pulmonary rehabilitation and symptom management  

For advanced ILD, lung transplantation may be considered in selected patients after a thorough assessment.

Care is typically coordinated by a specialist ILD team, ensuring patients receive expert, personalised management. 

The outlook for ILD

ILD is generally a progressive disease. This means it tends to worsen over time. However, the rate of progression can vary widely between individuals depending on the specific type of ILD and the response to treatment.

In IPF, without treatment, the average survival time after diagnosis is three to five years. However, newer therapies, earlier diagnosis and better supportive care have improved outcomes for many patients.

Other forms of ILD, particularly those related to autoimmune conditions or hypersensitivity pneumonitis, may have a more variable course. Some may improve with treatments, while others may progress more slowly or rapidly.

Even when a cure is not possible, good symptom control and careful support can help many individuals continue leading fulfilling and active lives for as long as possible.

How to reduce your risk of ILD

While not all cases of ILD can be prevented, there are practical steps you can take to reduce your risk:

• Avoid smoking and exposure to second-hand smoke
• Use protective equipment (eg masks, respirators) when working with dust, mould, or harmful chemicals
• Be cautious with medications — inform your doctor if you experience lung-related symptoms after starting a new medication
• Manage autoimmune diseases effectively with medical supervision
• Monitor your lung health if you have a family history of ILD or a history of occupational exposures
• Stay fit and healthy — maintaining good general health can help your lungs cope better with any disease process

Is there ongoing research into ILD treatments?

There is extensive ongoing research aimed at improving the diagnosis, treatment and outcomes of people living with ILD.

In recent years, there have been significant advances, particularly in the treatment of IPF with antifibrotic medications like nintedanib and pirfenidone, which can slow disease progression. 

Researchers are now exploring newer antifibrotic drugs that may be even more effective or better tolerated. In addition to antifibrotics, research studies are investigating:

• Newer antifibrotic agents that may be more effective or better tolerated
• New immune-modulating therapies for inflammatory forms of ILD
• Combination therapies that target both inflammation and fibrosis 
• Biomarkers to predict disease behaviour and guide personalised treatment
• Stem cell therapies and regenerative medicine approaches to repair damaged lung tissue
• Inhaled therapies to deliver treatments directly to the lungs

Clinical trials are also exploring treatments for related symptoms such as chronic cough. 

Final thoughts

ILD is a complex group of serious lung conditions that can significantly affect breathing and quality of life. Although many forms of ILD are progressive, early diagnosis, specialist management and appropriate treatment can help slow disease progression, manage symptoms and maintain independence for as long as possible.