Pathology of lung allografts in children and young adults

Pediatric lung transplantation: perspectives for the pathologist

Lung transplantation offers life-saving and life-extending treatment for children and adolescents with congenital and acquired forms of pulmonary and pulmonary vascular disease, for whom medical therapy is ineffective or insufficient for sustained response. This review summarizes the pathology related to lung transplantation for the practicing pediatric pathologist and also highlights aspects of lung transplantation unique to the pediatric population. Clinical issues related to availability of organs, candidate eligibility, surgical technique, and postoperative monitoring are discussed. Pathologic evaluation of routine surveillance transbronchial biopsies requires attention to acute cellular rejection, opportunistic infection, and other forms of acute and resolving lung injury. These findings are correlated in some cases with endobronchial biopsies and bronchoalveolar lavage as adjunctive tools in surveillance. Open or thoracoscopic biopsies also have diagnostic utility in cases with acute or chronic graft deterioration of uncertain etiology. Future challenges in pediatric lung transplantation are similar to those in the adult population, with continued efforts focused on prolonging graft survival, prevention of bronchiolitis obliterans syndrome due to chronic cellular rejection, and evaluation of humoral rejection.

HLA-specific antibodies are risk factors for lymphocytic bronchiolitis and chronic lung allograft dysfunction

Bronchiolitis obliterans syndrome (BOS) represents a major limitation in lung transplantation. While acute rejection is widely considered the most important risk factor for BOS, the impact of HLA-specific antibodies is less understood. Of 51 lung recipients who were prospectively tested during a 4.2 +/- 1.6-year period, 14 patients developed HLA-specific antibodies. A multi-factorial analysis was performed to correlate the prevalence of BOS with HLA antibodies, persistent-recurrent acute rejection (ACR-PR), lymphocytic bronchiolitis, and HLA-A, -B, and -DR mismatches. HLA-specific antibodies were associated with ACR-PR (10/14 vs. 11/37 with no antibodies, p < 0.05), lymphocytic bronchiolitis (8/14 vs. 10/37, p < 0.05), and BOS (10/14, vs. 9/37, p < 0.005). Other risk factors for BOS were: lymphocytic bronchiolitis (13/18 vs. 6/33 with no lymphocytic bronchiolitis, p < 0.0001), ACR-PR (12/21 vs. 7/30 with no ACR-PR, p < 0.05), and the number of HLA-DR mismatches (1.7 +/- 0.48 in BOS vs. 1.2 +/- 0.63 without BOS, p < 0.05). The presence of antibodies exhibited a cumulative effect on BOS when it was associated with either lymphocytic bronchiolitis or ACR-PR. The complex relationship between the development of HLA antibodies and acute and chronic lung allograft rejection determines the importance of post-transplant screening for HLA-specific antibodies as a prognostic element for lung allograft outcome.

Mortality after pediatric lung transplantation: autopsies vs. clinical impression

Appreciable mortality accompanies pediatric lung and heart-lung transplantation. The objective of this investigation was to compare the clinical impression of causes of death with autopsy findings in all pediatric lung or heart lung transplant recipients who had an autopsy performed between 1985-2002 at the Children's Hospital of Pittsburgh. Medical records and autopsy findings were reviewed. Thirty recipients with autopsies had 33 transplant procedures: heart-lung (16), double lung (14), repeat lung (2), and repeat heart-lung (1). Perioperative deaths occurred in 8 children, most often precipitated by graft dysfunction. Early deaths (2 weeks-1 year) occurred in 12 children resulting from infection. Late deaths (greater than 1 year) occurred in 10 children. Bronchiolitis obliterans complicated by infection was the major cause of death in these recipients. An autopsy confirmed the clinical impression of cause of death in 29/30 and added significant supplemental information in 16 cases. Unsuspected factors contributing to death included donor lung abnormalities, concurrent infection, and cardiovascular disease. Postmortem examination remains a critical component to augment the understanding of causes of death following pediatric thoracic transplantation.

Inhaled corticosteroids and the treatment of lymphocytic bronchiolitis following lung transplantation

Airway rejection after lung transplantation is recognized histologically as lymphocytic bronchiolitis (LB). We hypothesized that inhaled steroids could control LB and that changes in exhaled nitric oxide (eNO) would correlate with the development of LB and also have a role in monitoring response to treatment. A cohort of 120 lung transplant (LT) recipients attending for review and biopsy had eNO measurements, FEV1, lavage microbiology, and biopsy histology performed prospectively. Wilcoxon signed-rank test was used to assess the significance of changes in eNO and FEV1. The coefficient of reproducibility of eNO measurement in stable recipients was 2.36 ppb. Fourteen developed graft dysfunction owing to isolated LB and were treated with inhaled budesonide 800 microg twice daily. They showed significant increases in eNO at diagnosis, median (range) 10.9 ppb (4.6 to 48) ppb compared with baseline, 4.33 (1.0 to 10.76), p = 0.008, and a decrease in FEV1. After inhaled treatment, both eNO and FEV1 returned to baseline values. Seven developed acute vascular rejection (with or without LB) and were treated with oral corticosteroids; no changes in eNO occurred at diagnosis or after treatment. Serial eNO measurements provide a useful noninvasive method of identifying airway inflammation in LT recipients. Inhaled budesonide may be a useful addition to systemic immunosuppressants in controlling airway inflammation posttransplant.

Constrictive (obliterative) bronchiolitis: diagnosis, etiology, and a critical review of the literature

Constrictive bronchiolitis (CB) (or obliterative bronchiolitis) designates inflammation and fibrosis occurring predominantly in the walls and contiguous tissues of membranous and respiratory bronchioles, with resultant narrowing of their lumens. It differs from bronchiolitis obliterans-organizing pneumonia in its histopathology and clinical course. Most cases of CB occur in the setting of organ transplants, particularly lung and heart-lung transplants, but also in bone marrow transplants. Other bona fide cases are rare: infection, particularly viral infection, appears to be a well-documented precursor to CB in children, but not in immunocompetent adults. Constrictive bronchiolitis also has been reported in the course of rheumatoid arthritis, in certain other autoimmune diseases such as pemphigus vulgaris, after inhalation of toxic gases such as nitrogen oxide, after ingestion of certain drugs or medicinal agents such as Sauropus androgynous, and as a cryptogenic illness. Recent reports suggest that CB, as defined by clinical criteria (that is, bronchiolitis obliterans syndrome), is very common in lung allograft recipients who survive more than 5 years and, although it is associated with significant mortality, it also can be clinically stable. Furthermore, with the current practice of close monitoring of these patients, it appears that CB may now be diagnosed at an earlier stage, at which resolution, or at least stabilization of progression, is possible. A histopathologic diagnosis of CB in lung transplant and other patients may be difficult to make due to the patchy distribution of lesions, the technical difficulty in obtaining tissue in late lesions with extensive fibrosis, and the failure to recognize lesions. With regard to the last of these, in early stages of disease, CB may be subtle and easily missed in routine hematoxylin-eosin-stained specimens, while in advanced stages the disease may be equally difficult to diagnose if the patchy scarring in the lung is interpreted as nonspecific. The relative loss of bronchioles and the relationship of the scars to contiguous arteries should signal the need for elastic stains to look for the residual elastica of the bronchioles amidst the foci of fibrosis. Increasingly, clinical grounds, including pulmonary functions studies and high-resolution computed tomography findings, are proving to be relatively sensitive methods of detecting CB. Finally, the progressive airway destruction in chronic transplantation rejection appears to be a T-cell-mediated process. The "active" form of constrictive bronchiolitis, with attendant lymphocytic inflammation of the airways, likely precedes the "inactive" or scarred form of constrictive bronchiolitis.