Interstitial lung disease (ILD) - Symptoms, Causes, Complications, Treatment and Prevention

Definition of interstitial lung disease



Interstitial lung disease (ILD) or Idiopathic Interstitial Pneumonia (IIP) is an umbrella term for a large group of diseases that cause scarring (fibrosis) of the lungs. This results in increased stiffness and loss of usual lung elasticity, a decrease in the oxygenation process, and resulting breathlessness and cough, leading to a poor quality of life. ILDs are usually treated by specialized pulmonologists. 

History of interstitial lung disease

In 1872, a German physician, Von Buhl, described some cases of desquamative pneumonia in his letters to a friend, which may be the first description of pulmonary fibrosis. In 1892, William Osler (regarded as the father of modern medicine), in his medical textbook, coined the term Cirrhosis of the Lung. Following the above two physicians, many terms were used for these diseases, including Hamman-Rich syndrome, cryptogenic fibrosing alveolitis and muscular cirrhosis of the lung, etc.

Prevalence of interstitial lung disease

Worldwide

According to a recent study using Global Burden of Disease data, the global incidence of ILDs has increased by 51% over the last decade, from 313.2 cases in 1990 to 207.2 cases per 100,000 cases in 2019. These published estimates show a noticeable variance in ILD epidemiology between countries.

According to a study of 3,089 participants, the prevalence of interstitial lung disease (ILD) in India ranges from 49.0 to 98.1 per 100,000 persons, with an annual incidence of 10.1 to 20.2 per 100,000 people. Another study indicated that the incidence of ILD in India rose from 24.7 to 33.6 per 100,000 individuals between 2005 and 2020.

Nomenclature and classification of interstitial lung disease

Idiopathic interstitial pneumonia (IIP) is a diverse collection of non-neoplastic illnesses that cause lung parenchymal damage through various patterns of inflammation and fibrosis. The interstitium, which comprises the space between the epithelial and endothelial basement membranes, is the major site of damage in IIPs. However, these illnesses typically affect not only the interstitium but also the airspaces, peripheral airways, arteries, and epithelial and endothelial linings.

The new ATS/ERS classification comprises the following clinicopathologic entities in order of relative frequency:

• Idiopathic pulmonary fibrosis (IPF)
• Non-specific interstitial pneumonia (NSIP)
• Cryptogenic organizing pneumonia (COP)
• Acute interstitial pneumonia (AIP)
• Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD)
• Desquamative interstitial pneumonia (DIP)
• Lymphoid interstitial pneumonia (LIP)
  

Interstitial lung disease symptoms

Some people may not experience any symptoms at first, but as the disease progresses, symptoms may appear. Although the symptoms of interstitial lung disease might vary from person to person, the following are the most common ones:

• Shortness of breath: It may initially start during exertion and later may progress to present at rest. 
• Dry cough: It may become wet when there is any secondary infection.
• Chest discomfort: Tightness or heaviness in the chest region
• Labored breathing: Difficulty or impairment in breathing
• Clubbing: A downward sloping of the nails and a broadening and rounding of the tips of the toes and fingers
• Fatigue: Extreme weakness and tiredness
• Weight loss: It may be due to the inability to consume food due to severe breathlessness.

These symptoms may be present along with the symptoms of underlying disease, such as joint pains in rheumatoid arthritis. In the late stages, patients may develop symptoms due to failure of other organs, the most common being heart failure.

Interstitial lung disease causes and risk factors

Anyone can get ILD, including children. Many things can cause or increase the risk of developing ILD, including:

• Family history: If a close relative has an ILD, the likelihood of developing an ILD in an individual increases. People may be more susceptible to developing lung scar tissue if they have genetic mutations.
• Occupation and Environment: Exposure to hazardous materials (grain dust, silica dust, indoor hot tubs, asbestos fibers, radiation treatments) accidentally or in the workplace, such as Occupational Lung Diseases (asbestosis and hypersensitivity pneumonitis), may increase the risk of developing ILD. 
• Certain medications: Exposure to certain medications or therapies, such as chemotherapy or radiotherapy, may increase the risk of developing ILD. 
• Autoimmune diseases: Some autoimmune diseases, such as scleroderma, sarcoidosis, rheumatoid Arthritis, mixed connective tissue disease, dermatomyositis, polymyositis, and Sjogren's syndrome, are also causes of ILD. 
• Smoking: It is the most common cause of respiratory complaints worldwide. It not only causes ILD but also aggravates pre-existing disease. 
• Gender: Certain interstitial lung diseases (ILDs) are more prevalent in either gender. Men are more likely to get idiopathic pulmonary fibrosis (IPF) and experience more severe symptoms from it. Lymphangioleiomyomatosis (LAM) is more prevalent in females. In addition, women are more likely to suffer from various autoimmune illnesses and connective tissue disorders that lead to ILDs.



Unfortunately, in most cases, the ultimate cause may not be known, such as in Idiopathic Pulmonary Fibrosis (IPF), which is the most severe type of lung fibrosis or scarring.

Interstitial lung disease complications

Without proper treatment, interstitial lung disease (ILD) can lead to the following complications:

• Pneumothorax: It is also known as a collapsed lung and happens when air escapes from the lungs. The space between the lung and the chest wall is then filled with air. This buildup of air puts pressure on the lung, preventing it from expanding as much as it would when one takes a breath. 
• Pulmonary hypertension: It is a condition that affects the blood vessels of the lungs. It occurs when the blood pressure in the lungs exceeds normal levels. 
• Respiratory failure: It is a life-threatening (severe) condition which causes difficulty breathing on one's own. Respiratory failure occurs when the lungs are not able to get enough oxygen into the blood. 
• Lung cancer: It is a form of cancer that occurs when abnormal cells grow aberrant (uncontrollably) in the lungs. It is a significant health problem that can result in severe injury or death. 
• Venous thromboembolism: Venous thromboembolism (VTE) is a medical condition that occurs when a blood clot forms within a vein. VTE comprises of both deep vein thrombosis (DVT) and pulmonary embolism (PE). 
• Right-sided heart failure: Right heart failure (RHF) is a clinical syndrome associated with symptoms and signs caused by dysfunction and/or overload of the right heart structures, primarily the right ventricle (RV). This results in systemic venous hypertension, peripheral oedema, and, ultimately, the right heart's impaired ability to provide tissue perfusion. 
  

Interstitial lung disease diagnosis

As the symptoms of ILD are not much different from other pulmonary diseases, a high index of suspicion during the patient's initial visit following thorough history taking and physical examination is the cornerstone for early diagnosis. The diagnosis of ILD involves the following: 

• Medical history
• Family history
• Physical examination
• Blood tests
• Arterial blood gas
• Complete blood count
• Urea and electrolytes
• Liver function tests
• Calcium
• Erythrocyte sedimentation rate
• C reactive protein 
• Sputum analysis 
• Imaging tests
• Chest X-rays
• Computed tomography (CT) scan
• High Resolution Computed Tomography (HRCT)
• Pulmonary function tests 
• Spirometry
• Peak flow monitoring
• Bronchoscopy
• Bronchoalveolar lavage (BAL) 
• Lung biopsy
  

Interstitial lung disease treatment

Treatment for ILDs depends on the underlying cause and the severity of the symptoms. Treatment for ILDs does not cure lung damage but may prevent it from worsening and allow one to breathe more easily. Below are the treatment options for interstitial lung disease (ILD): 

• Nonpharmacological therapy
• Cessation of smoking 
• Avoiding exposure to harmful particles 
• Pharmacological therapy
• Bronchodilators
• Corticosteroids
• Antifibrotics
• Oxygen therapy
• Pulmonary rehabilitation
• Lung transplant
  

Interstitial lung disease prevention

There is no way to prevent interstitial lung disease (ILD) caused by the genes in the body. Some ILDs can be prevented in the following ways: 

• Avoiding smoking 
• Avoiding toxins that can harm the lungs in the surroundings or workplace.
• Patients may need to have additional lung tests to see whether their lung damage is worsening.
• Getting Pneumococcal, influenza, and COVID-19 vaccinations can help avoid lung infections that can cause further lung damage.
  

Difference between ILD and COPD

Interstitial lung disease vs COPD

Interstitial lung disease (ILD) and Chronic obstructive pulmonary disease (COPD) are chronic lung conditions that can make it difficult to breathe. The illnesses, however, differ in terms of their underlying causes and the areas of the lungs affected. Below are some of the parameters that help in differentiating ILD and COPD:

Outcome

The overall outcome in ILDs depends on various factors, such as age at onset of symptoms, underlying other co-morbidities, the stage of fibrosis and lung function at the time of diagnosis, and the progression of symptoms despite possible the best treatment. As ILD causes and treatments are still under constant research, patients should never undermine the importance of constant vigilance of their symptoms.

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