Bronchiolitis obliterans.

Hospital survival rates in experienced lung transplantation centers exceed 90%, but late survival for lung allograft recipients is clouded by bronchiolitis obliterans syndrome (BOS). Bronchiolitis obliterans is the characteristic pathological feature of this late syndrome of chronic lung allograft dysfunction, which is thought to represent chronic lung allograft rejection. BOS seems to affect all lung transplant recipients, including single, bilateral, and heart-lung transplantation patients. Although specific symptoms are lacking, patients typically experience worsening respiratory debilitation, with the characteristic physiological hallmark being airflow limitation, as evidenced by progressive decline in several spirometric parameters. Because the clinical and functional aspects of this syndrome are not always coexistent with the typical pathology, a staging and classification system was devised that allows for diagnosis of BOS even in the absence of bronchiolitis obliterans. Data from Stanford University, featuring very prolonged follow-up, have shown that actuarial freedom from OB is only 29% at 5 years post lung transplantation. Overwhelming experimental evidence suggest that OB is the result of an immune-mediated process, and therefore the usual treatment for this condition has been to increase the maintenance immunosuppression regimen, and to further augment immunosuppression using a variety of strategies. Most of these strategies have been effective in achieving some reduction in the rate of decline in graft function, although true "cure" of BOS has been rare. Re-transplantation has been the most aggressive therapeutic strategy for OB, but for a number of logistic reasons, is applicable for only a tiny minority of lung transplant recipients with OB.