Bronchiolitis obliterans is a condition marked by diffuse lung damage that can affect both infants and adults and immunocompetent and immunocompromised patients. It is characterized by injury to the small airways (bronchioles) resulting in progressive narrowing of bronchial lumens. Causes include inhalation injury (eg, chlorine, ammonia, diacetyl), infection (eg, adenovirus, influenza, parainfluenza, respiratory syncytial virus), medications (eg, rituximab, sulfasalazine), toxic fumes (eg, silos, welders, military), and graft-versus-host disease following bone marrow or rejection following lung transplantation. Bronchiolitis obliterans may also been seen in the setting of autoimmune diseases like rheumatoid arthritis.

Diacetyl is a flavoring compound often used in e-cigarettes / vape pens. Its former use in factories manufacturing microwave popcorn was associated with diagnoses of bronchiolitis obliterans, thus sometimes known as "popcorn lung."

The clinical syndrome manifests as an airway obstruction, cough, and slowly progressive dyspnea (weeks to months), with radiographic examination showing normal or hyperinflation of the lungs. Tachypnea, crackles, and/or wheezing may be evident on physical examination.

Related topic: Bronchiolitis