Bronchiolitis obliterans syndrome – Diagnostics – Overview of Information and Clinical Research

Understanding how bronchiolitis obliterans syndrome is diagnosed can help patients and their families navigate this challenging condition with greater confidence. Early detection through proper testing is essential for slowing the disease’s progression, though many people may not experience obvious symptoms at first. This rare lung condition requires a combination of diagnostic approaches to confirm its presence and distinguish it from other respiratory diseases.

Introduction: Who Should Seek Diagnostic Testing

Bronchiolitis obliterans syndrome is a condition that specifically occurs after lung transplantation or hematopoietic stem cell transplantation, representing a form of chronic rejection. Anyone who has undergone one of these transplant procedures should be aware that regular monitoring becomes part of their long-term care plan.^[1]

The majority of lung transplant recipients who survive for the long term will eventually develop some degree of this syndrome. More than half of all lung transplant recipients develop bronchiolitis obliterans syndrome within five years after their procedure, with the average diagnosis occurring between 16 and 20 months post-transplant. However, the condition has been reported as early as three months following transplantation.^[1]

People who have received hematopoietic stem cell transplantation are also at risk, though less frequently. About 5% to 14% of these recipients develop the syndrome, which can appear several months to years after transplantation. This represents a form of pulmonary graft-versus-host disease, where the donated cells react against the recipient’s lung tissue.^[1]

Seeking diagnostic testing becomes advisable when respiratory symptoms begin to emerge or worsen. Many people with bronchiolitis obliterans syndrome may not notice symptoms initially, which makes scheduled follow-up testing after transplantation particularly important. When symptoms do appear, they typically include a dry cough, shortness of breath especially during physical activity, wheezing, and feeling tired. These symptoms generally worsen over weeks to months rather than improving.^[3]^[4]

⚠️ Important

Bronchiolitis obliterans syndrome can sometimes look like an infection at first, making proper diagnostic testing essential to distinguish between the two conditions. The disease progresses differently for each person—one individual might remain in an early stage for quite some time, while another may move quickly from one stage to a more advanced one.

Transplant recipients should maintain regular contact with their healthcare team and report any new or worsening respiratory symptoms promptly. Because the condition can be detected before obvious symptoms develop, adhering to scheduled monitoring appointments is crucial for early identification and intervention.

Classic Diagnostic Methods

Diagnosing bronchiolitis obliterans syndrome requires a combination of different testing approaches, as no single test can definitively confirm the condition. Healthcare providers use multiple tools to build a complete picture of what is happening in the lungs.

Pulmonary Function Testing

The foundation of diagnosing bronchiolitis obliterans syndrome lies in pulmonary function testing, particularly a test called spirometry. This breathing test measures how much air a person can breathe out and how quickly they can do so. In bronchiolitis obliterans syndrome, spirometry reveals a pattern of airflow obstruction—the airways become narrower, making it harder for air to flow out of the lungs.^[1]^[4]

Spirometry is especially valuable because it can determine how severe the disease has become. The test provides objective measurements that doctors can track over time to see whether lung function is declining, staying stable, or possibly improving with treatment. For lung transplant recipients, comparing current spirometry results to their best measurements after transplant helps identify when the syndrome is developing.^[3]

In children, the type of breathing test used depends on the child’s age. For younger children who cannot perform standard spirometry, an infant pulmonary function test may be used instead. Children aged five and older can usually complete regular lung function tests, which are blowing tests that show whether any blockage exists in the small airways.^[7]

Computed Tomography (CT) Scan

A CT scan of the chest provides detailed pictures of the lungs and can reveal characteristic patterns associated with bronchiolitis obliterans syndrome. Unlike a standard chest X-ray, which often appears normal in people with this condition, a CT scan can detect subtle changes in the small airways.^[4]^[6]

The CT scan is typically performed in a special way that captures images both when the person breathes in and when they breathe out. This technique helps identify areas of air trapping—regions of the lung where air gets stuck because the small airways are blocked. The scan may also show a pattern called mosaic attenuation, where some parts of the lung appear darker than others, along with bronchiectasis (widening of the airways) and thickening of the bronchial walls.^[4]

For children undergoing evaluation, the CT scan takes detailed pictures of their lungs during breathing in and out, providing similar information about airway obstruction and damage.^[7]

Lung Biopsy

While pulmonary function tests and CT scans provide strong evidence of bronchiolitis obliterans syndrome, sometimes a lung biopsy is needed to confirm the diagnosis with certainty. During this procedure, a surgeon removes a small sample of lung tissue for examination under a microscope. The biopsy can definitively show the characteristic scarring and narrowing of the small airways that define this condition.^[4]^[6]

However, lung biopsies are not always necessary. If the CT scan shows sufficient evidence of bronchiolitis obliterans syndrome and the clinical picture fits, doctors may diagnose the condition without performing a biopsy. This is because biopsies carry risks and may not be essential when other evidence is conclusive.^[7]

When a biopsy is performed in children, a surgeon makes a small cut in the chest and removes tissue from the lung while the child is under general anesthesia, meaning they won’t be aware of what’s happening. Sometimes this can be done using keyhole surgery, which involves smaller incisions.^[7]

Medical History and Physical Examination

The diagnostic process always begins with a thorough review of the patient’s medical history and current symptoms. Doctors need to know when symptoms started, how they have progressed, and what exposures or medical events might have triggered the condition. For transplant recipients, the timing of symptoms relative to the transplant procedure is particularly important.^[6]^[7]

Understanding the patient’s complete medical background helps doctors distinguish bronchiolitis obliterans syndrome from other conditions that might cause similar symptoms. This is especially important because symptoms like coughing, wheezing, and shortness of breath can occur with many different respiratory problems.

Differential Diagnosis

One of the challenges in diagnosing bronchiolitis obliterans syndrome is that its symptoms can resemble other respiratory conditions, particularly asthma. Both conditions can cause wheezing, coughing, and breathing difficulties. However, bronchiolitis obliterans syndrome shows an obstructive pattern on pulmonary function tests that does not improve when bronchodilator medications (drugs that open the airways) are given. This helps distinguish it from asthma, which typically does respond to bronchodilators.^[4]

Doctors must also consider whether symptoms might be caused by an infection, especially in transplant recipients who take immunosuppressive medications that make them more vulnerable to infections. The diagnostic process aims to rule out these other possibilities while looking for the specific pattern of small airway scarring that characterizes bronchiolitis obliterans syndrome.

Diagnostics for Clinical Trial Qualification

For patients considering participation in clinical trials investigating new treatments for bronchiolitis obliterans syndrome, specific diagnostic criteria must be met to qualify for enrollment. Clinical trials use standardized testing protocols to ensure that all participants have confirmed disease and similar baseline characteristics.

Spirometry remains the cornerstone test for qualifying patients for clinical trials. Researchers need objective measurements of airflow obstruction to determine whether someone meets the criteria for enrollment. Most clinical trials require patients to have documented decline in lung function compared to their best post-transplant values, typically measuring a specific decrease in forced expiratory volume in one second (FEV1), which is the amount of air a person can forcefully exhale in the first second of the test.^[3]^[12]

CT scanning often serves as a secondary requirement for clinical trial participation. Trials may require imaging evidence of the characteristic patterns associated with bronchiolitis obliterans syndrome, such as air trapping or mosaic attenuation. This helps ensure that enrolled patients truly have the syndrome rather than another condition affecting lung function.

Clinical trials may also require patients to undergo additional testing beyond standard diagnostic procedures. This could include more detailed lung function measurements, blood tests to assess inflammation or immune system activity, or specialized imaging studies. These additional tests help researchers gather comprehensive data about the disease and how it responds to the treatment being studied.

The timing of diagnosis relative to trial enrollment is also important. Some trials specifically target patients with early-stage disease, while others focus on those with more advanced bronchiolitis obliterans syndrome. The stage of disease is typically determined using a combination of spirometry results and clinical symptoms, with established classification systems that categorize patients based on the degree of lung function decline.^[3]^[12]

⚠️ Important

Patients interested in clinical trials should discuss this option with their transplant team as early as possible. Meeting enrollment criteria often requires having up-to-date diagnostic testing, and the window of opportunity for certain trials may be limited based on how long ago the diagnosis was made or how quickly the disease is progressing.

Before enrolling in any clinical trial, patients undergo a thorough screening process to confirm they meet all eligibility requirements. This screening may involve repeating some diagnostic tests even if they were recently performed, to ensure the most current information is available to researchers. Patients must also meet other criteria related to their overall health status, current medications, and ability to comply with study requirements such as regular monitoring visits.

Prognosis and Survival Rate

Prognosis

The outlook for patients with bronchiolitis obliterans syndrome varies considerably depending on several factors. The condition generally leads to a progressive decline in lung function over time, though the rate of decline differs among individuals. Some people may experience mild impairment with slow progression and relatively stable disease, while others face more rapid deterioration requiring aggressive intervention.^[5]^[11]

How quickly the disease progresses is not uniform—one person might stay in an early stage for an extended period, while another moves rapidly from one stage to more advanced stages. The disease cannot be reversed, meaning that lung damage already present is permanent. However, treatments can slow further worsening and help manage symptoms.^[3]^[4]

Several factors influence prognosis, including how early the condition is detected, how aggressively it is treated, and individual patient characteristics. Some forms of bronchiolitis obliterans, particularly obliterative bronchiolitis following a lung transplant, can be fatal if not treated. The prognosis can range from mild to severe impairment depending on the type and underlying cause of the condition.^[5]

In children with post-infectious bronchiolitis obliterans, the disease usually does not continue to worsen over years—most of the lung damage occurs during and shortly after the triggering infection. Some children have a mild form and can continue living without significant breathing problems or limitations to their daily activities. However, other children may develop a more severe form requiring oxygen or other breathing support throughout their lives.^[18]

Survival Rate

Among lung transplant recipients, bronchiolitis obliterans syndrome is the most common type of chronic rejection and a leading cause of death beyond the first year after transplantation. About 50% of people who receive lung transplants will develop some degree of bronchiolitis obliterans syndrome within five years of their transplant procedure. By ten years following lung transplantation, approximately 75% of recipients have developed the condition.^[3]^[4]

For recipients of hematopoietic stem cell transplantation, the occurrence is less common but still significant. About 10% of bone marrow transplant recipients develop bronchiolitis obliterans syndrome within five years of receiving their transplant.^[3]

While specific long-term survival statistics vary, outcomes are often poor for patients with advanced disease. Most people with progressive bronchiolitis obliterans syndrome face declining health over months to years. In severe cases where lung function continues to deteriorate despite treatment, a lung transplant may be the only remaining option, though this carries its own risks and challenges.^[4]

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