Epidemiology

Bronchiolitis obliterans (BO) is a rare chronic obstructive lung disease of the bronchioles and smaller airways. An insult to the lower respiratory tract occurs, resulting in fibrosis of the small airways. In the nontransplant patient, BO most commonly occurs in the pediatric population after respiratory infections, particularly adenovirus, but also Mycoplasma, measles, legionella, influenza, and pertussis; other causes include inflammatory diseases (juvenile rheumatoid arthritis, systemic lupus erythematosus [Chapter 152], scleroderma [Chapter 154], Stevens-Johnson syndrome [Chapter 146]), and inhalation of toxin fumes (NO₂, NH₃) (see Table 386-1 on the Nelson Textbook of Pediatrics website at www.expertconsult.com). Bronchiolitis obliterans syndrome (BOS), a clinical entity that relates to graft deterioration after transplantation due to progressive airway, is increasingly recognized as a long-term complication of lung and bone marrow transplantation; more than one third of survivors of lung transplant can develop this disorder. BO occurs in all age groups, and the prevalence in 1 pediatric autopsy series was 2/1,000. BOS appears to be more common among older children and adolescents than infants and toddlers. There is some evidence that postinfectious obliterans may be more common in the southern hemisphere and among persons of Asian descent.

Pathogenesis

After the initial insult, inflammation affecting terminal bronchioles, respiratory bronchioles, and alveolar ducts can result in the obliteration of the airway lumen (Fig. 386-1). Epithelial damage resulting in abnormal repair is characteristic of BO. Complete or partial obstruction of the airway lumen can result in air trapping or atelectasis. Bronchiolitis obliterans organizing pneumonia (BOOP) is a fibrosing lung disease that includes the histologic features of BO with extension of the inflammatory process from distal alveolar ducts into alveoli and proliferation of fibroblasts. BOS appears histologically similar to BO. The etiology of BOS is unclear, however, and may be unrelated to the mechanisms responsible for BO in nontransplant patients.

Figure 386-1 Complete obliteration of airway lumen with fibromyxoid tissue in lung transplant recipient with bronchiolitis obliterans.

(From Kurland G, Michelson P: Bronchiolitis obliterans in children, Pediatr Pulmonol 39:193–208, 2005.)

Clinical Manifestations and Diagnosis