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.