BOS UPDATE Bronchiolitis Obliterans Syndrome 2001: An Update of the Diagnostic Criteria

Bronchiolitis obliterans (BO) is a major cause of allograft dysfunction in lung and heart lung transplant recipients. Clinically, progressive airflow limitation develops because of small airway obstruction. The disease has a variable course. Some patients experience rapid loss of lung function and respiratory failure. Others experience either slow progression or intermittent loss of function with long plateaus during which pulmonary function is stable. Histologic confirmation is difficult because transbronchial biopsy specimens often are not sufficiently sensitive for diagnosis. Because BO is difficult to document histologically, in 1993 a committee sponsored by the International Society for Heart and Lung Transplantation (ISHLT) proposed a clinical description of BO, termed bronchiolitis obliterans syndrome (BOS) and defined by pulmonary function changes rather than histology. Although this system does not require histologic diagnosis, it does recognize it. Transplant centers worldwide have adopted the BOS system as a descriptor of lung allograft dysfunction. This allows centers to use a common language to compare program results. In the years since publication of the BOS system, transplant scientists have studied basic and clinical aspects of lung transplant BO. In this document, we update and summarize new information obtained from this research and incorporate, where appropriate, the results into the BOS criteria. The document will include the following topics: (1) criteria for BOS, (2) BOS considerations in pediatric patients, (3) risk factors for BOS, (4) pathology of BO, (5) surrogate markers for BOS, (6) confounding factors in making a BOS diagnosis, and (7) assessment of response to treatment of BOS.