Overview of pulmonary fibrosis

Pulmonary fibrosis is a general term referring to a lung disease that occurs when the lung tissue is damaged or scarred. This thickens the lung tissue and hinders the lungs’ normal function. Pulmonary fibrosis can remain stable or deteriorate quickly. Such a deterioration causes shortness of breath and fatigue when carrying out day-to-day activities. If you are experiencing any of these symptoms, you should see your GP. If they believe you have pulmonary fibrosis they will refer you for diagnostic tests, such as:

• Pulmonary function tests
• Imaging tests (chest X-ray or CT scan (computed tomography))
• Lung biopsy

Accurate and early diagnosis is important to prevent further deterioration of the disease. It is also vital for a timely selection of treatment, thereby improving patient outcomes.¹ Diagnosis of pulmonary fibrosis can be challenging due to its variable and complex nature. In addition, it is similar to many other lung diseases such as chronic obstructive pulmonary disease (COPD). Lung damage caused by pulmonary fibrosis cannot be repaired. However, medication and therapies can slow the rate of fibrosis and reduce symptoms. If the cause of pulmonary fibrosis is known, resolving this issue will reduce symptoms. However, most of the time the cause of pulmonary fibrosis is unknown. In those cases, it is termed idiopathic pulmonary fibrosis (IPF).

Imaging tests to diagnose pulmonary fibrosis

Chest X-ray 

A chest X-ray is used to produce an image of your heart, lungs and chest. For example, if you have symptoms of shortness of breath, the first imaging test undertaken would be a chest X-ray. It is used to help doctors determine if the symptoms are caused by a heart or lung condition or something else.²  Such problems include a buildup of fluid or cancer. However, chest X-rays do not show the lungs in great detail. This handicap can sometimes be the reason for missing early or mild cases of pulmonary fibrosis. Therefore, if IPF is suspected, it will then be followed up by a CT scan. 

CT scan

A CT (computed tomography) scan is similar to an X-ray except it can take more images from a range of angles. These images can then be compiled by a computer to create a more detailed image of your lungs. This is used to help doctors identify scar damage and observe how much damage to the lungs has occurred. Some types of fibrosis even have certain patterns, which can help diagnose the problem.³  Something called ground-glass opacities can be seen on a CT scan. These opacities are hazy areas that indicate to physicians that an inflammation is present in the lungs.

One type of CT scan which is especially useful is called HRCT (high-resolution computed tomography). It shows the highest level of detail. An HRCT can allow doctors to observe:

• Reticular opacities - net-like structures that indicate the thickening of lung tissue
• Honeycombing - clusters of cystic air spaces in a honeycomb pattern. This pattern indicates irreversible scarring 
• Traction bronchiectasis - irreversible dilation of the bronchi (airways to the lungs).⁴

These structures can only be seen with an HRCT scan and not by using an X-ray

Other imaging methods 

It is rare for imaging tests other than chest X-rays or CT scans to be used. However, MRI (magnetic resonance imaging) is sometimes used in the clinic. It produces 3D images like a CT scan, providing a detailed look into the lungs. It is useful as MRI exposes the patient to lower amounts of radiation compared to other imaging tests. This makes it ideal for paediatric examinations, pregnant women and patients requiring continuous monitoring.⁵ 

However, it is not normally used because it provides poor imaging of the lung interstitium (area in the lungs involved in the exchange of gases). This poor imaging makes a clear diagnosis difficult.⁶ In addition, PET scans are occasionally used to rule out other possible problems like cancer or infection. However, PET scans cannot be used to directly diagnose pulmonary fibrosis. 

Pulmonary function tests (PFT) to diagnose pulmonary fibrosis

Spirometer

A spirometer is a small piece of apparatus with a mouthpiece. When exhaling into the mouthpiece, a spirometer can be used to determine lung function. A spirometer can measure:

• FVC (forced vital capacity) - is how much air the lungs can breathe out
• FEV1 (forced expiratory volume in one second) - is the amount of air breathed out in the first second

If FVC is reduced but FEV1 remains the same, it indicates pulmonary fibrosis.⁷ It can tell doctors if there is damage to the lungs and the extent of impairment to lung function. 

Diffusion capacity testing

Diffusion capacity testing, also known as lung diffusion testing (DLCO), tells a healthcare provider how well your lungs are working. However, unlike a spirometer, it uses a gas called carbon monoxide to measure diffusion. Diffusion is a process by which oxygen moves from the lungs to the blood. This is essential to ensure oxygen can reach all the tissues of the body. In pulmonary fibrosis, the transfer of oxygen is impaired. This is because the lung tissue thickens which creates a greater distance for the oxygen to move. Therefore, a reduced diffusion capacity is a hallmark of pulmonary fibrosis due to the thickening and scarring of lung tissue.⁷

Biopsies to diagnose pulmonary fibrosis 

Surgical lung biopsy

A surgical lung biopsy is when a small amount of lung tissue is removed by surgery. This sample is then examined by a pathologist under a microscope to diagnose pulmonary fibrosis.⁸ It is only considered for patients where non-invasive imaging tests have been inconclusive. For these patients, it is the only certain method of diagnosis. In most cases, non-invasive tests can identify pulmonary fibrosis. Therefore, surgical lung biopsy is rarely used.  It can cause postoperative complications, such as bleeding and infection. In addition, it requires a moderate recovery time post-surgery. Since there is a risk of postoperative complications, it cannot be used in weakened or immunocompromised individuals.

Transbronchial lung biopsy 

Transbronchial lung biopsy also removes a small amount of lung tissue. However, this is done through bronchoscopy instead. A bronchoscope is a small tube inserted through the nose or mouth and down the trachea to the lungs. Small forceps are then inserted through the tube to take samples of lung tissue. Since this method is non-invasive, there is a lower chance of postoperative complications. However, transbronchial lung biopsy is used less frequently than surgical lung biopsy. This is because it has a limited ability to obtain large tissue samples which are necessary.⁹ They make the diagnosis more accurate and increase the likelihood of diagnosis.  

Cryobiopsy

Recently, transbronchial lung cryobiopsy (TBLC) has been introduced as a method for diagnosing lung diseases. It involves using a cryoprobe to freeze and remove a tissue sample. Unlike traditional transbronchial lung biopsy, it can obtain a large tissue sample and is less invasive than surgical lung biopsy.¹⁰ Due to its recent introduction, it is not always the most commonly used biopsy technique.

Differential diagnosis of pulmonary fibrosis

It is important to distinguish pulmonary fibrosis from other lung diseases for the most accurate diagnosis and effective treatment plan. IPF (idiopathic pulmonary fibrosis) is the most common type of pulmonary fibrosis. However, other interstitial lung diseases (ILDs) share similar features, making them difficult to distinguish. One differing feature is the patient demographic. IPF is most common in people assigned male at birth over the age of 70 and is rare in those under 50 years old.¹¹ Unlike IPF, other ILDs are very often associated with

• Autoimmune diseases
• Environmental exposures
• Side effects of medications

This means it is important for a physician to know your medical history. This way, the physician can rule out other illnesses that could cause your symptoms before making a definitive diagnosis. As previously mentioned, IPF is also distinguished from other ILDs by a distinct pattern seen in HRCT and biopsies.

Summary

To diagnose pulmonary fibrosis a range of imaging tests, pulmonary function tests and sometimes biopsies can be used. Pulmonary function tests are often used first in diagnosis to measure how well the lungs are functioning

If there is a reduced function of the lungs, imaging tests are used to acquire detailed pictures of the lungs by radiologists. X-rays are used first, then CT scans which show a more detailed image of the lungs to identify damaged lung tissue 

Finally, if these diagnosis methods cannot give a conclusive diagnosis a biopsy will be undertaken. Previously, surgical lung biopsy was the most common but with newer better technologies cryo biopsy is becoming more popular 

All of these procedures allow healthcare providers to make an accurate diagnosis and therefore an informed decision about the treatment of patients