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Page 2 Bronchiolar
Airway Disorders and Bronchiolitis Obliterans
RADIOGRAPHIC ASSESSMENT The chest radiograph in patients with constrictive bronchiolitis may be normal, may show hyperinflation, or a nodular or reticulonodular pattern. The secondary pulmonary lobule visualized by the high-resolution CT scan has become an important diagnostic finding for the assessment of transplantation-related obliterative bronchiolitis. The structure is a polyhedral shaped unit measuring 1.0 to 2.5 centimeters on each side (17). The pulmonary veins and lymphatics are located at the periphery of the lobules. The center of the lobule contains the pulmonary artery and a bronchiole of about one millimeter in diameter. Abnormalities in the periphery can be utilized to diagnose an interstitial process or lymphangitic carcinomatosis while abnormalities in the center of the lobule are utilized for the diagnosis of a bronchiolar disorder. For transplantation ñ related obliterative bronchiolitis, high-resolution CT findings include central bronchodilatation, hyperlucency, mosaic phenomenon, peribronchial, and perivascular infiltrates (18). The CT findings of the bronchiolar disorders can be classified into three major patterns (19). The first pattern consists of centrilobular nodules and branching lines, which usually represents an active, cellular bronchiolitis. The second classification consists of ground-glass attenuation and consolidation, bronchiolitis obliterans organizing pneumonia is typical of this pattern. The third pattern is most appropriate for this patient, areas of low attenuation and mosaic perfusion. The form of bronchiolitis characteristically associated with low attenuation and mosaic perfusion is constrictive bronchiolitis (obliterative bronchiolitis). Additional chest CT findings of constrictive bronchiolitis may be divided into direct and indirect signs. The only direct sign is uncommon and related to thickening of the wall of the bronchioles. Indirect signs of bronchiolar dilatation and mosaic perfusion are commonly seen. Mosaic perfusion is due to decreased perfusion of areas with bronchiolar obstruction and flow redistribution to normal areas. The third indirect sign is air trapping from partial airway obstruction due to constrictive bronchiolitis, best seen on expiratory CT scans. In many patients with constrictive bronchiolitis only one of the indirect signs may be seen. In a study of 15 patients with obliterative bronchiolitis, the majority of patients had irregular patches of radiolucency with ill-defined edges (20). In a report of two patients with bronchiolitis obliterans, the chest roentgenogram was normal in both (21), but the high-resolution CT showed multiple secondary lobules of low attenuation. One patient had lupus erythematosus and the other had 15 years of chronic cough, dyspnea and airflow obstruction. In a study of 18 patients with bronchiolitis obliterans, patchy areas of decreased parenchymal attenuation was the most common finding (22). In a description of the natural history of cryptogenic bronchiolitis obliterans in a patient followed for 24 years, the chest radiograph remained normal while the chest CT showed irregular areas of low attenuation throughout the lungs with Hounsfield numbers typical of emphysema, but no bullae (23). This pattern was a mosaic of polygonal regions of high and low attenuation measuring 2.5 centimeters in diameter. Chest CT scans taking during suspended expiration have currently become useful for detection of bronchiolitis obliterans. In a report of a 65 year-old woman with idiopathic bronchiolitis obliterans, the CT scan showed normal findings during a full inspiration, but during a suspended full expiration, there were multiple, focal, lobule-sized lucencies consistent with extensive lobular air trapping (24). Clinical Classification of the Bronchiolar diseases A clinical classification is developed from information regarding causes or associated systemic disorders, Table 4. BRONCHIOLITIS Adult bronchiolitis may be acute or chronic. Acute bronchiolitis is usually thought of as a disease of infants caused by respiratory syncytial virus (25). For adults, cellular bronchiolitis as suggested by Colby is an appropriate term and is defined as acute or chronic inflammation involving small airways sometimes with mural or peribronchiolar fibrosis (13). There are several causes of bronchiolitis in the adult, infections are probably the most common cause of bronchiolitis, and include such agents as parainfluenza type 1, 2, and 3; mycoplasma pneumoniae and adenoviruses (25). Uncommon infectious agents would include mumps, varicella zoster virus, influenza A and B, rhinoviruses, and rarely the enteroviruses. Protozoal bronchiolitis due to Encephalitozoon hellem has been reported in a patient with HIV infection (26). DIFFUSE PANBRONCHIOLITIS Extensive study of the clinical, pathological, radiographic and treatment of diffuse panbronchiolitis continues. In 1994, Iwata and associates reviewed this disorder and described seven additional patients (12). Diffuse panbronchiolitis is a clinicopathologic entity with symptoms of chronic cough, sputum and dyspnea, crackles and rhonchi by chest examination, radiographic findings of hyperinflation and bilateral, small nodular opacities, and airflow obstruction by a decreased FEV1. Hypercapnia and cor pulmonale occur late. Additional clinical findings include chronic paranasal sinusitis, increased cold hemagglutinin titer, increased CD4/CD8 ratio, increased immunoglobulin A, and HLA-Bw54 antigen occurring in about 63 percent of patients (27). Histologically, there is chronic inflammation of the respiratory bronchioles with distinctive interstitial accumulation of foam cells in the walls of respiratory bronchioles, adjacent alveolar ducts and alveoli. The disorder is largely restricted to Japan, although it has been reported among Chinese and Koreans, in Europe and the United States (28). There has been a report of the disorder occurring in a 47 year-old Hispanic man who had chronic sinusitis since his early twenties (28). Although he had been born in the United States, he had been a merchant marine for three years with extensive travel to Japan, Vietnam and China. Whether the travel history to Japan was a risk factor or coincidental in the development of the disease could not be determined. The disorder is progressive with ten-year survival of only 33 in the 1980's. The development of Pseudomonas infection is a bad prognostic sign, the mean survival is about 3 years. The introduction of low-dose, long-term (200 mg every 8 hours) administration of erythromycin has proven effective and has resulted in improved ten-year survival. It has been suggested that erythromycin impairs pulmonary inflammation by an alteration of neutrophil chemotactic factors leading to reduction of the migration of neutrophils to inflammatory sites (29). A study of 33 patients with diffuse panbronchiolitis showed that after treatment with erythromycin, there was a decrease in the number of lymphocytes and activated CD8 cells, and an increase in the CD4/CD8 ratio in the lavage fluid (30). In a similar study of nine patients (31), it was found that leukotriene B4 was increased in the lavage fluid of patients with diffuse panbronchiolitis and may have a role in the recruitment of neutrophils into the airways. The leukotriene B4 levels were reduced after erythromycin treatment. These authors suggested that erythromycin might inhibit the production of this mediator which would restrict neutrophil accumulation and airway inflammation. In a study of 64 patients with chronic airflow disease and 32 patients with diffuse panbronchiolitis, Koyama and colleagues (32) found that patients with diffuse panbronchiolitis had less airway reactivity to methacholine than those with chronic airflow obstruction. The investigators suggested that the difference was related to the pathogenesis of the two diseases and the nature of bronchiolar inflammation. For example, the inflammation of diffuse panbronchiolitis is associated with chronic lower respiratory tract infection while the inflammation related to chronic obstructive pulmonary disease is related to cigarette smoking. Recurrence of diffuse panbronchiolitis in a newly transplanted lung has been reported in a 38 year-old man (33). The patient developed recurrent episodes of acute sinusitis in early childhood and a chest radiograph at age 13 that showed bilateral reticulonodular opacities. The sputum became colonized with Pseudomonas aeruginosa at 31 years of age. He underwent bilateral sequential lung transplantation and ten weeks later; he developed bronchospasm, hypoxemia and a decrease in FEV1 with lung biopsy showing diffuse panbronchiolitis in the newly transplanted lung. A study of 18 patients with diffuse panbronchiolitis showed that after three months of therapy, there was a decrease in high resolution CT scores for extent of small nodular opacities and bronchiolar inflammation, severity of peri-airway thickening, and extent of mucus plugging (34). There was also a corresponding significant improvement in pulmonary function testing suggesting that these airway lesions were reversible with erythromycin therapy. The severity and extent of airway ectasia showed no response to erythromycin therapy, suggesting an irreversible airway lesion.
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