What Is Interstitial Lung Disease?

Overview

Interstitial (in-tur-STISH-ul) lung disease is an umbrella term for over 100 different lung conditions,¹ involving inflammation and scar tissue formation in the interstitial lung tissue (pulmonary fibrosis). The interstitial tissue of the lung is the network of tissue that supports the air sacs (alveoli), where the exchange of oxygen for carbon dioxide takes place. When scar tissue forms within this network, the tissue thickens, hardens and becomes less elastic (Asthma and Lung UK). This reduces the lung’s ability to expand sufficiently to allow normal intake of air. These structural changes to the alveoli also inhibit optimal gas exchange in the lungs (National Heart, Lung, and Blood institute). The result is shallow or laboured breathing and decreased oxygen entering the body.   

The most common Interstitial lung disease conditions found in Europe are Idiopathic pulmonary fibrosis (IPF) and Sarcoidosis.² 

Causes of interstitial lung disease

The cause of Interstitial lung disease is not known³ but according to the American Lung Association, the following factors are thought to increase risk of its development:

• genetics
• certain medications
• certain medical treatments such as chemotherapy and radiotherapy
• smoking 
• exposure to asbestos
• exposure to other hazardous occupational materials such as silica, dust arising from wood, metal, coal, sand, farming or livestock⁴
• co-existence of other conditions such as:
  • Hypersensitivity pneumonitis, a condition caused by exposure to allergens such as household mould, bird droppings or bird feathers
  • Autoimmune diseases such as rheumatoid arthritis (a connective tissue disease)⁵

There is ongoing research into whether Gastro-oesophageal reflux disease (GERD) is a risk factor for some Interstitial lung disease conditions. Findings from studies carried out so far have not been conclusive and further research is required.¹

In some cases, such as Idiopathic pulmonary fibrosis and Sarcoidosis, the causes and risk factors are unknown.^{3, 6}

Signs and symptoms of Interstitial lung disease

Signs and symptoms of Interstitial lung disease are often non-specific and common to many respiratory conditions. These include:

• Breathlessness
• Cough
• Fatigue
• Insomnia
• Reflux
• Psychological problems such as anxiety and depression^7,8

Management and treatment for Interstitial lung disease

The damage caused to lungs by Interstitial lung disease is often permanent and cannot be repaired. The condition is also usually progressive (it gets worse over time). Treatment therefore focuses on slowing disease progression to prevent further lung damage occurring, as well as reducing symptoms.

Medication used to slow the disease progression varies depending on the type of condition involved and its severity. Differential diagnosis with a specific condition is therefore fundamental to the success of treatment.¹ Conditions involving lung inflammation may respond to treatment with anti-inflammatory medication such as steroids,¹ whilst conditions involving fibrotic changes may instead be treated with anti-fibrotic therapy.³ 

Treatment focusing on providing relief from symptoms and improving quality of life may include oxygen therapy¹ and pulmonary rehabilitation.⁸ Pulmonary rehabilitation programmes provide education and advice - for example techniques to improve efficiency of breathing and reduce feelings of breathlessness, advice on self-management of respiratory conditions, as well as structured exercise programmes to improve endurance.

In extreme cases, lung transplantation may be recommended.¹

Treatment may involve a multidisciplinary team of health care providers (specialists from different fields who work together) and may take place in a specialist Interstitial lung disease clinic.⁴

Diagnosis of Interstitial lung disease

Specific and accurate diagnosis of Interstitial lung disease is important in order for the correct management approach to be taken¹ and the following elements may be included in an assessment:

• History taking including relevant occupational information
• Physical examination including listening to breath sounds
• Lung function tests (to check how well the lungs are working)
• Blood tests
• Chest X-rays
• CT (computerised tomography) scan
• Bronchoscopy - insertion of a thin tube with a camera attached via the nose or mouth to reach the lung, in order to provide visual information on the lung tissue and/or remove a small piece of tissue for further examination
• surgical lung biopsy - removal of small piece of tissue for further examination, carried out as surgery¹

The findings of all test and assessment results will be combined to help the clinician to differentiate between different conditions which are similar in nature.¹ However, differences between conditions can be subtle and diagnostic criteria vary. As a result, accurate diagnosis can be challenging, even for experienced clinicians, and initial misdiagnoses are not uncommon. Due to this, and the time required to undergo all tests and diagnostic procedures and wait for interpretation of results, there is frequently significant delay in reaching the true diagnosis.⁹

As Interstitial lung disease is progressive, it is important for it to be diagnosed as early as possible and treatment started to prevent deterioration. Research shows that a delay in referral to a specialist unit for treatment is linked to worse prognosis, and it is recommended that suspected cases are referred without delay.⁴ However, early diagnosis is hampered by a frequent lack of specific symptoms during the early stages of the disease. Indeed, a significant proportion of patients are not diagnosed with Interstitial lung disease until receiving acute care for an exacerbation (a sudden worsening of symptoms).¹⁰

Risk factors

How and why Interstitial lung disease develops is not fully understood.³ Genetics may contribute, as may the presence of other health conditions and the use of certain medications or treatments.

In addition, the exposure to certain environmental and lifestyle factors may increase risk of development of these conditions, and these include:

• Smoking 
• Exposure to hazardous substances such as asbestos, wood/metal dust or other occupational materials
• Inhalation of allergens such as bird droppings, bird feathers and mould 

(American Lung Association)

Complications

Interstitial lung disease can range significantly in severity, from mild to life-threatening. Complications include pulmonary hypertension (high pressure in the blood vessels running from the heart to the lung) and potentially life-threatening conditions of heart failure and respiratory failure. (American Lung Association)

Interstitial lung disease patients can experience exacerbations¹¹ (acute episodes of worsening of symptoms) and these can result in admission to hospital. Depending on the severity, admission to the Intensive Care Unit (ICU) may be required for treatments such as ventilation.¹⁰

While the mechanism for these flare-ups is not fully understood, it is thought that infection, air pollution and micro-aspiration may contribute, (when small volumes of liquid are aspirated or drawn into the lungs). However, many exacerbations are considered idiopathic - ie. have no known cause.¹⁰

FAQs

How can I prevent Interstitial lung disease

The causes and mechanisms involved in Interstitial lung disease are complex and not fully understood. They may include genetics, co-existence of other conditions and exposure to certain medications/treatments. It is thought that certain environmental and lifestyle factors - such as smoking and exposure to hazardous substances and allergens - may also increase the risk of development of Interstitial lung disease and should be avoided.

How common is Interstitial lung disease?

The lung conditions classed as Interstitial lung disease are rare, but there is insufficient data available to specify exactly how many people worldwide have them. There are a number of barriers to the recording of true data in this area, including a lack of consensus in classification and diagnostic criteria,² and a shortage of data in this area from developing countries.¹² 

Global figures from studies show a range of 6 - 98 people per 100,000¹³ having Interstitial lung disease, with figures from The International Respiratory Coalition showing an average of 53.7 cases per 100,000 in Europe. However, figures vary considerably from country to country and a recent review of worldwide study data found differences between individual European countries ranging from 6.27 - 71 people per 100,000.² It is not yet possible to confirm whether this variation between populations is due to true differences in demographics and environmental exposures, or due to differences in diagnosis, classification and recording of data.² Further research is needed for greater clarification.

When should I see a doctor?

The symptoms of Interstitial lung disease are non-specific and common to many respiratory conditions. They often do not appear until the disease has already significantly progressed. As a result, diagnosis is challenging and often missed or delayed.⁹

The damage caused by Interstitial lung disease can be irreversible, and so early diagnosis is critical. It is therefore important to consult a healthcare provider if you experience any ongoing respiratory problems, including shortness of breath or persistent cough.

Summary

Interstitial lung disease is an umbrella term for a number of different chronic lung conditions which involve inflammation and fibrosis of the lungs. The structural changes that take place with these diseases result in changes to respiratory function and a reduction in the amount of oxygen taken into the body. The main symptoms experienced are shortness of breath and cough. The damage caused by these conditions can be permanent, but treatment may be able to slow progression, as well as to reduce symptoms and improve quality of life.

Interstitial lung diseases can be challenging to diagnose as symptoms may not be experienced until significant damage to lung tissue has already occurred. If you experience ongoing respiratory symptoms, consult a Healthcare Practitioner for further advice.