Constrictive (obliterative) bronchiolitis.

Constrictive bronchiolitis (CB), also termed in lung transplant patients obliterative bronchiolitis, is inflammation and fibrosis occurring predominantly in the walls and contiguous tissues of membranous and respiratory bronchioles with resultant narrowing of their lumens. CB is found in a variety of settings, most often as a complication of lung and heart-lung transplantation (affecting 34% to 39% of patients, usually in the first 2 years after transplantation) and bone marrow transplantation, but also in rheumatoid arthritis, after inhalation of toxic agents such as nitrogen dioxide, after ingestion of certain drugs such as penicillamine and ingestion of the East Asian vegetable Sauropus androgynous, and as a rare complication of adenovirus, influenza type A, measles, and Mycoplasma pneumoniae infections in children. In lung transplants, CB is the single most important factor leading to death thereafter. In one study, the overall mortality rate was 25%. However, at the same time, 87% of patients who were asymptomatic and diagnosed solely by transbronchial biopsy had resolution or stabilization of disease. Decreases in FEV1 from baseline can be used to clinically support CB in transplant patients; the term bronchiolitis obliterans syndrome is used to denote this clinical dysfunction, and a grading system has been established for it that is now widely used in the literature. Significant risk factors for the development of CB in lung transplants include alloantigen-dependent and -independent mechanisms. In the former group are late acute rejection and HLA mismatches at the A loci; in the latter are ischemia/reperfusion injuries to airways that result from the transplantation surgery and cytomegalovirus infection.