RBILDRespiratory Bronchiolitis Interstitial Lung Disease
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In patients with RBILD, smoking cessation is a mainstay of therapy, and frequently results in stabilization or resolution of symptoms.
It is worth reemphasizing that RBILD is histologically indistinguishable from incidental RB, and a diagnosis of RBILD relies on incorporation of clinical and radiologic data.
(19) There is significant clinical overlap between DIP and RBILD, with both patient populations similarly presenting with exertional dyspnea, cough, and diffuse ground-glass opacities on chest imaging studies; however, the degree of physiologic impairment tends to be worse in DIP, with those patients suffering from more severely reduced diffusing capacity of the lungs for carbon monoxide.
Some authors still use the extent of fibrosis as at least a partial criterion for morphologic separation of RB from RBILD. (9) However, studies based on lung cancer resection specimens have shown that fine fibrosis in the alveolar walls around respiratory bronchioles is in fact very common in the lungs of cigarette smokers who have no clinical evidence of an ILD.
The HRCT findings in RBILD are fairly similar to those of RB, but they often show a greater extent of ground glass opacities extending to the lower zones, and sometimes mild reticulation in the lower zones.
Because the essence of RBF is a focal form of interstitial fibrosis caused by cigarette smoke, one could adopt the Katzenstein et al (3) usage and label these cases as "smoking-related interstitial fibrosis," but "smoking-related interstitial fibrosis"/"smoking-related ILD" is a term that gets used informally for a variety of forms of ILD in cigarette smokers, (11) including RBILD, DIP, Langerhans cell histiocytosis, and sometimes even combined pulmonary fibrosis and emphysema.
Differential diagnosis also includes usual interstitial pneumonia and RBILD. (29,312-314)
The authors designated this finding peribronchiolar metaplasia-related interstitial lung disease because of the analogy with respiratory bronchiolitis and RBILD, in which respiratory bronchiolitis is a common incidental finding in smokers and RBILD is the smoking-associated clinically significant interstitial lung disease.
Although uncommon conditions such as diffuse idiopathic neuroendocrine cell hyperplasia and diffuse panbronchiolitis have histologic features that allow for relatively specific diagnoses, and although some conditions such as mineral dust-associated small airways disease, RBILD, granulomatous bronchiolitis, eosinophilic bronchiolitis, and fol licular bronchiolitis have histologic features that may be diagnostic in the appropriate clinical and radiologic setting, most cellular and fibrotic changes found in small airways disease are nonspecific.
We were asked to specifically address the issue of fibrosis and its significance in RBILD in this brief review, but in doing so, it has become apparent that there are 2 pools of knowledge: 1 related to interstitial lung diseases and their pathologic correlates, and the other related to COPD and its pathologic correlates.
Myers et al (1) suggested that extension of the fibrosing and inflammatory process into adjacent alveolar walls separated RBILD from RB.
Subsequent pathologic descriptions of RBILD have reported largely similar findings (Table 1; Figures 1 through 4), albeit with some variation from report to report and also with incorporation of the changing definitions of RB (see below).