Case of the Month

Respiratory bronchiolitis interstitial lung disease (RB-ILD)

Figure 1. Chest x-ray, Lat, and PA views.  A diffuse reticulonodular pattern is seen, there is a lineal band at the LLL.

Figure 2. Axial non-enhanced chest CT image (lung window) Bronchial wall thickening, centrilobular nodules, and ground-glass opacities associated with upper lobe centrilobular emphysema are seen.

Figure 3. Coronal non-enhanced chest CT image (lung window) Note the GGO centrilobular micronodules.

Bronchiolitis is an inflammation and/or fibrosis that involves the bronchioles and the alveolar ducts. This entity is divided into two broad categories at the pathologic examination, cellular bronchiolitis, and constrictive (fibrotic) bronchiolitis. Cellular bronchiolitis includes acute and chronic infectious bronchiolitis that it is usually caused by bacteria, mycobacteria, fungus, and virus and it is the most common type of bronchiolitis; aspiration bronchiolitis that is due to chronic aspiration; respiratory bronchiolitis associated with tobacco smoking; hypersensitivity pneumonitis (allergic); follicular bronchiolitis in immunosuppressed states and panbronchiolitis which cause is unknown. On the other hand, constrictive bronchiolitis can be idiopathic, autoimmune, or post-transplantation (bone marrow and lung) (1).

Respiratory bronchiolitis (RB) is a rare, mild inflammatory pulmonary disorder that occurs in current or former heavy smokers between the third and sixth decades with no gender predilection (2).

RB is a form of smoking-induced interstitial lung disease, it is a histologic marker of smoking status and it is present essentially in all current cigarette smokers and half of the ex-smokers. Although, it can be seen in nonsmokers who have been exposed to environmental insults or secondhand smoke (3,4).

This entity is usually silent and discovered incidentally, but in a subset of patients accounts for clinical interstitial lung disease causing complaints of persistent cough and exertional dyspnea, developing over a course of weeks or months. These patients generally have a mixed pattern in the pulmonary function testing, predominantly obstructive abnormalities, often combined with hyperinflation and impaired diffusion capacity (DLco), with diffuse changes on chest imaging such as ground-glass opacities, centrilobular micronodules, and peribronchiolar thickening, often accompanied by tobacco-related centrilobular emphysema. This disease should be called respiratory bronchiolitis with fibrosis-interstitial lung disease (RB-ILD) (5).

Chest radiographs in patients with RB-ILD typically show fine reticulonodular interstitial opacities, while on HRCT central and peripheral bronchial wall thickening, centrilobular nodules, and ground-glass opacities associated with upper lobe centrilobular emphysema are most frequently reported.

On HRCT imaging, RB is usually characterized by bronchial wall thickening and poorly defined ground glass centrilobular nodules, and sometimes by more extensive ground-glass opacities, which are typically upper zonal and midzonal (2).

The course of RB-ILD is heterogenous, some patients respond favorably to corticosteroids and/or smoking cessation, but often there is no functional improvement and the disease progresses despite smoking cessation and treatment. The indications of treatment are often marginal, but the smoking cessation is considered the most important factor in the management of RB-ILD, although it is not yet completely understood wheter smoking cessation alone con improve outcomes in RB-ILD. The prognosis for these patients is good with a long life expectancy (5).

1. Winningham PJ, Martínez-Jiménez S, Rosado-de-Christenson ML, Betancourt SL, Restrepo CS, Eraso A. Bronchiolitis: A Practical Approach for the General Radiologist. RadioGraphics. 2017;37(3):777-94.
2. Sieminska A, Kuziemski K. Respiratory bronchiolitis-interstitial lung disease. Orphanet J Rare Dis. diciembre de 2014;9(1):106. 3. Konopka KE, Myers JL. A Review of Smoking-Related Interstitial Fibrosis, Respiratory Bronchiolitis, and Desquamative Interstitial Pneumonia: Overlapping Histology and Confusing Terminology. Arch Pathol Lab Med. 2018;142(10):1177-81. 4.
3. Fraig M, Shreesha U, Savici D, Katzenstein A-LA. Respiratory Bronchiolitis: A Clinicopathologic Study in Current Smokers, Ex-Smokers, and Never-Smokers. Am J Surg Pathol. 2002;26(5):647-53. 5.
4. Portnoy J, Veraldi KL, Schwarz MI, Cool CD, Curran-Everett D, Cherniack RM, et al. Respiratory Bronchiolitis-Interstitial Lung Disease. Chest. 2007;131(3):664-71.