Churg, Muller and Wright published a superb update on RB/ILD in the January 2010 Arch Pathol Lab Med which is essential background to Katzenstein's article in Human Pathology on "occult interstitial fibrosis in smokers." Do yourself a favor and just read my summary of the Katzenstein paper (skip the original) in light of the excellent update by Dr. Churg.
RB/ILD can be described as a clinicopathologic entity characterized by clinically evident interstitial lung disease (originally described by Myers et al. as restrictive pattern of changes by PFTs and/or bilateral, poorly defined centrilobular nodules and ground-glass opacities mainly involving lower lung fields by HRCT) and histologic changes listed below with specific exclusion other forms of ILD. Morphologic changes include:
- clusters of pigmented alveolar macrophages in respiratory bronchiolar lumens--the fundamental requirement for diagnosis
- mild chronic interstitial inflammation, mild interstitial fibrosis and type 2 pneumocyte hyperplasia in bronchioles and adjacent alveolar walls
But since RB/ILD is a disease of cigarette smokers (and heavy smokers at that--reported mean pack-years between 29 to 54), these patients also are at risk for COPD--"a process that potentially confounds the diagnois of RBILD pathologically, radiologically, and on pulmonary function testing."
Can we separate RBILD from RB? Based on their review, the authors find that there are no histologic features that separate RBILD from RB. Moreover, although some authors have contended that clinical RBILD is associated with a greater degree of fibrosis histologically, this point is in doubt since many lungs from smokers also show some (usually mild) alveolar wall fibrosis (thus see comments about the Katzenstein article below).
What is the relationship between RB/RBILD and centrilobular emphysema? The authors note that emphysematous foci are (as one would expect) a common finding in patients with RB/RBILD and that foci of centrilobular emphysema can be associated with fibrosis. Which begs the question "whether some of the descriptions of alveolar wall fibrosis associated with RB/RBILD may really be misclassifications of fibrotic emphysematous foci." In addition, previous studies including careful evaluation and grading of fibrosis and grading respiratory and membranous bronchioles and correlation with PFTs showed a correlation with obstructive PFT abnormalities related to COPD.
Since many of these patients have clinical, functional and histologic features of COPD, the authors argue that "only restrictive or mixed restrictive/obstructive patterns, or (less certainly) a markedly reduced diffusing capacity in the absence of significant airflow obstruction, allow the diagnosis of RBILD." (with the presence of RB histologic features described above on biopsy).
Churg A, Muller NL, Wright JL. Respiratory bronchiolitis/interstitial lung disease. Arch Pathol Lab Med 2010;134:27-32.
Which leads to the paper by Katzenstein et al.
This study consisted of 23 consecutive lobectomy specimens for malignant neoplasms with extensive and systematic sampling of non-neoplastic lung (27 sections per case!). None of the patients had clinical evidence of ILD. Also, all patients had CT scans but none showed radiographic evidence of diffuse ILD. 20/23 patients were smokers, 10 current. One interesting point in this article is the proportion of women to men: 15 subjects were women versus 8 men. This seems unusual both in terms of a series of lobectomies for malignancy as well as a study of ILD since men are usually more common to both. The authors evaluated the specimens for interstitial fibrosis (recognized at low power), fibroblast foci, peribrochiolar metaplasia, honeycomb change, emphysema, and respiratory bronchiolitis.
Based on the review by Churg et al. above, I have a hard time buying the authors' description of smoking-related interstitial fibrosis (SRIF) as a distinctive entity. They do note the similarity of their findings with the study of Yousem (which was also cited by Churg et al) which he termed "RBILD with fibrosis." All 12 cases with "significant" fibrosis and/or emphysema occurred in patients with a smoking history and, moreover, all of these cases had associated emphysema and RB. Furthermore, in 8 of 9 patients with "SRIF" with PFTs, 6 showed mild-to-moderate obstructive defects and 2 were normal!
I'm not sure why this was published. It doesn't seem to add much to existing knowledge about smoking-related lung disease and, basically, the authors have reported a group of patients with a history of smoking and morphologic and functional changes of RB and COPD in the background of lung cancer. Why this was "surprising" to them (as in the title) is surprising to me. I'd like to know the authors' opinion why obstructive PFT defects are present in their patients with significant (but clinically occult) interstitial fibrosis. Finally, Dr. Yousem already did this study in 2006 (and as a "proposal" for "a lesion distinct from fibrotic nonspecific interstitial pneumonia" it wasn't convincing then too).
Katzenstein A-L A, Mukhopadhyay S, Zanardi C, Dexter E. Clinically occult interstitial fibrosis in smokers: classification and significance of a surprisingly common finding in lobectomy specimens. Hum Pathol 2010;41:316-325.