Subtypes and Causes: Why Did This Happen?

Understanding why you developed bronchiolitis obliterans is a key step in managing the condition. Because this disease is rare outside of lung transplants, doctors look for specific triggers that may have caused the initial injury to your small airways. Scientists generally group these causes into common cause categories ^[1][2]. Identifying your category helps your care team predict how the disease might behave and what steps you can take to protect your remaining lung function. Keep in mind that some patients have overlapping triggers, and many cases remain cryptogenic (having no identifiable cause).

1. Occupational and Inhalational Exposures

This category occurs when you breathe in toxic substances that irritate and scar the tiny bronchioles.

• Flavoring Chemicals: One of the most well-known causes is diacetyl (and its relative, 2,3-pentanedione), chemicals used to give foods a buttery flavor ^[3][4]. This was famously linked to “Popcorn Lung” in workers at microwave popcorn plants, but it is also found in coffee processing and other food production ^[3][5].
• Toxic Gases and Dusts: Inhalation of nitrogen dioxide (found in farm silos), sulfur mustard, or certain metal dusts can cause acute injury that leads to permanent scarring ^[6][2].
• Military Burn Pits: Veterans may have been exposed to complex mixtures of desert dust and smoke from burn pits. While research is ongoing and findings vary by study, some personnel have been diagnosed with constrictive bronchiolitis following these exposures ^[7].

Disease Behavior: In these cases, the disease often evolves slowly after years of exposure. The most critical intervention is complete removal from the exposure source to prevent further damage ^[8][6]. You should ask your doctor for a referral to an occupational/environmental medicine specialist to safely document exposures and guide workplace accommodations.

2. Post-Infectious (PIBO)

Post-infectious bronchiolitis obliterans (PIBO) occurs after a severe respiratory infection that permanently scars the airways during the healing process ^[9].

• Childhood Origins: Most cases are diagnosed in infants or young children who survive a life-threatening bout of adenovirus or Mycoplasma pneumoniae ^[9][10].
• Risk Factors: Children who required a ventilator (breathing machine) or heavy oxygen support during their infection are at much higher risk for developing PIBO ^[11][12].
• Adults: While less common in adults, severe viral or bacterial infections can occasionally lead to similar airway scarring ^[13][14].

Disease Behavior: While PIBO causes significant lung impairment, many children find their condition appears to stabilize or improve as they grow. This apparent improvement is often because their lungs physically enlarge as they grow, not because the established scar tissue reverses ^[15][16].

3. Autoimmune and Connective Tissue Diseases

Sometimes, the body’s own immune system attacks the small airways as part of a systemic (body-wide) condition. This is most common in:

• Rheumatoid Arthritis (RA): This is the most frequent autoimmune cause. It often affects women in their 50s and can present as a “fixed” narrowing of the airways that doesn’t respond well to standard asthma inhalers ^[17][18].
• Sjögren’s Syndrome: A condition characterized by dry eyes and mouth that can also cause inflammation in the lung’s small airways ^[18][19].

Disease Behavior: In RA-related cases, the lung function often remains stable for long periods, although symptoms like shortness of breath may persist ^[17]. Treatment focuses on managing the underlying autoimmune disease, sometimes using specialist-directed immunosuppressants ^[19][17]. Note that negative blood tests for rheumatoid factor or anti-CCP do not completely rule out an autoimmune cause, and positive tests do not prove the airway disease is caused by it. Diagnosis often requires a rheumatologist.

4. Drug-Induced Bronchiolitis Obliterans

Certain medications can trigger airway scarring as a rare side effect ^[2].

• Traditional Medications: Drugs like penicillamine (used for RA or Wilson’s disease) and gold salts were historically linked to this condition ^[2].
• Modern Therapies: Newer cancer treatments known as immune-checkpoint inhibitors (such as pembrolizumab or nivolumab) have had rare reported immune-related cases of bronchiolitis obliterans ^[20].

Disease Behavior: If a medication is the cause, stopping the drug is the first step. You must not stop a prescribed medication on your own. You must contact your prescriber urgently, especially an oncologist, because substitution or tapering may be needed and stopping a life-saving drug abruptly carries severe risks. Because the scarring is physical (fibrosis), stopping the medication does not always reverse the damage already done to the lungs ^[20].