Diffuse panbronchiolitis (DPB) is a rare condition characterized by inflammation of the small airways of the lungs (bronchiolitis) and chronic sinusitis. It mainly occurs among the Japanese but has been reported in other populations. Symptoms typically develop anywhere from the teenage years to the fifth decade of life and are slowly progressive over months to years. Common symptoms include chronic sinusitis, a productive cough (producing mucus), breathlessness with exertion, wheezing, and weight loss (especially as symptoms worsen). The exact cause of DPB is not known, but a variety of genetic, environmental, and systemic factors appear to contribute to the condition. Treatment involves long-term use of macrolide antibiotics, which reportedly dramatically improves the long-term outcome. If untreated, DPB leads to bronchiectasis, progressive respiratory failure and death over the course of a few years.

The main treatment that has been recommended for diffuse panbronchiolitis (DPB) is the use of macrolide antibiotics. Erythromycin is typically the first drug of choice. A different macrolide antibiotic may be used if erythromycin is not well-tolerated or if a person doesn't improve after several weeks of therapy. The best duration of macrolide therapy is not known, but most patients are treated for a minimum of six months. Therapy is continued until symptoms, imaging findings, and lung function measurements are improved or stable. In the majority of patients, therapy is stopped after two years. However, in patients with advanced disease, therapy is continued indefinitely. Other therapies, such as bronchodilator medications and bronchial hygiene (airway clearance techniques), may be useful for some people.