Pathologically DPB is characterized by thickening of the walls of terminal and respiratory bronchioles by lymphocytes, plasma cells, and histiocytes. Intramural fibrosis may be present and, in combination with the mural infiltrate, results in significant airway narrowing. Apart from hyperinflation and the accumulation of lipid-laden macrophages distal alveolar ducts and lung parenchyma are usually normal.

The changes are more or less diffuse throughout the lungs resulting in roentgenographic evidence of a disseminated nodular pattern with lower zonal predominance. Evidence of hyperinflation is also present. HRCT can show four types of opacities: 1) small nodules around the end of bronchovascular branchings, 2) small nodules in the centrilobular area connected with small branching linear opacities, 3) nodules accompanied by small ductal opacities connected to proximal bronchovascular bundles, and 4) large cystic opacities accompanied by dilated proximal bronchi.

Most patients are between 30 and 60 years of age; the male ro female ratio is approximately 2 to 1. The chief clinical manifestations are dyspnea on exertion and cough, often with sputum production. Sinusitis is common. In the late stages, sputum culture often reveals the presence of microorganisms, especially P. aeruginosa, suggesting the development of airway colonzation. Pulmonary function tests show marked obstructive and mild restrictive impairment. Arterial hypoxemia is common.