Interstitial Lung Disease - Symptoms, Risk factors and Treatment

Interstitial lung disease refers to a large group of diseases involving the lung interstitium. The interstitium is the space in the tissue surrounding the tiny spaces for air exchange- the alveoli. 

In this disease, the lung interstitium becomes stiff and hard (pulmonary fibrosis), making breathing difficult.

What causes interstitial lung disease?

Interstitial lung disease occurs when there is something wrong with the body’s repair process. 

In interstitial lung disease, when there’s some injury to the lung tissue, there is excessive activation of inflammatory response that causes excess tissue production and fibrosis in the lungs as opposed to the normal repair process, in which there is a production of just the right amount of tissue to repair the injury. This injury can be caused due to some irritants such as cigarette smoke.

There are numerous different causes of interstitial lung disease. Each disease is named according to the underlying cause.

According to the underlying cause, interstitial fibrosis can be divided into two types: idiopathic and secondary.

When there’s no underlying cause determined, the disease is put under the idiopathic type which includes idiopathic interstitial pneumonia.

In secondary interstitial fibrosis, an underlying cause is identified. The diseases in this category include:

Interstitial lung disease due to autoimmune causes: 

In autoimmune diseases, your body's immune system misidentifies its own cells and starts to cause damage to them. Autoimmune diseases include:

• Rheumatoid arthritis
• Systemic lupus erythematosus (SLE)
• Polymyositis
• Systemic sclerosis

Interstitial lung disease due to inhaled substances :

There are substances, which if inhaled, in the form of dust or gas, can irritate and damage the lungs. They include:

• Tobacco smoke
• Silica causing silicosis
• Beryllium causes berylliosis

Asbestos causes asbestosis. Asbestos can also cause mesothelioma - a type of lung cancer.

Coal dust causes coal workers pneumoconiosis or black lung disease.

Other than these, organic dust and molds can cause a type of interstitial lung disease called hypersensitivity pneumonitis which can occur due to:

• Moldy hay (Farmer’s lung)
• Bird feathers and droppings (bird fancier’s lung)
• Moldy sugar cane (bagassosis)
• Cheese mold (cheese worker’s lung)
• Contaminated humidifier (humidifier’s lung)

Interstitial lung disease due to drugs:

Though not very common, certain drugs can cause interstitial lung disease such as:

• Chemotherapy drugs such as bleomycin
• Antibiotics 
• Antiarrhythmic drugs

Interstitial lung disease due to infections:

Infections can damage the lungs triggering interstitial lung disease. They can be;

• Tuberculosis caused by mycobacterium tuberculosis 
• COVID-19 caused by a coronavirus
• Influenza caused by Haemophilus influenzae
• Atypical pneumonia due to streptococcus, chlamydia, legionella

Interstitial lung disease due to inflammation:

Interstitial lung disease can be caused by a collection of inflammatory cells due to unknown reasons. The disease which represents this type is:

Sarcoidosis 

There can be many other causes than those listed above, as interstitial lung disease has over 200 different causes.

Symptoms of Interstitial lung disease:

The symptoms of interstitial lung disease include:

Shortness of breath

The main symptom of interstitial lung disease is breathlessness. You may find it difficult to breathe, and this can happen on doing activities such as walking or climbing up the stairs, etc. In severe cases, you may experience breathlessness even on resting.

Other than that, the symptoms may include:

• Dry cough

The complications of interstitial lung disease include:

Pulmonary Hypertension: It is a condition in which the blood pressure in the artery supplying your lungs is increased. In interstitial lung disease, the normal blood flow through the lungs is compromised due to fibrosis, which causes back pooling of blood in the pulmonary arteries.

Right-sided heart failure: The right side of the heart supplies blood to the pulmonary artery. When pulmonary hypertension takes place, the pressure in the right side of the heart increases, and it has to work harder. It causes a progressive increase in the size of the right side of the heart (cor pulmonale) and a reduction in its function referred to as heart failure. 

Hypoxemia: This means low levels of oxygen in the blood. Due to poor gas exchange in interstitial lung disease, hypoxemia can occur causing low levels of oxygen to reach different organs, having its own complications such as loss of consciousness or coma.

Diagnosis of interstitial lung disease:

The diagnosis of interstitial lung disease can involve a history, physical examination, and investigative tests. Your doctor may ask questions related to exposure to different toxic gases etc. For imaging of the lungs, usually, an X-Ray is done. In some cases, a lung biopsy can be done to determine the underlying cause.

Treatment of interstitial lung disease:

The treatment of interstitial lung disease primarily involves slowing the progression of the disease as the damage that has already occurred cannot be changed. If the disease is due to inhalation of a toxic substance, it is advised to remove the patient from the exposure of that substance immediately. Quitting smoking is highly encouraged as smoking damages the lungs and causes the progression of the disease. For this, psychotherapy may be recommended.

To slow the progression of interstitial lung disease, corticosteroid medications are prescribed. These medications slow down the immune system and the ongoing overactive inflammatory response, which is thought to be responsible for interstitial lung disease.

Moreover, supplemental oxygen may be given to increase oxygen levels in the blood.

Other than that, physical therapy is recommended.

The last and final resort for treating interstitial lung disease is a lung transplant.

Conclusion:

Interstitial lung disease is an umbrella term used for many different diseases. There are many different causes of interstitial lung disease. Timely diagnosis and treatment can help slow down the progression of the disease and improve quality of life.