Pathologic Criteria for the Diagnosis of Usual Interstitial Pneumonia vs Fibrotic Hypersensitivity Pneumonitis in Transbronchial Cryobiopsies
Abstract
Transbronchial cryobiopsy (TBCB) is increasingly used for the diagnosis of fibrosing interstitial pneumonias, but there are few detailed descriptions of the pathologic findings in such cases. It has been proposed that a combination of patchy fibrosis and fibroblast foci with an absence of alternative features is diagnostic of usual interstitial pneumonia (UIP; i.e., idiopathic pulmonary fibrosis, IPF) in TBCB.
Here we reviewed 121 TBCB in which a diagnosis of fibrotic hypersensitivity pneumonitis (FHP, N=83) or IPF (N=38) was made by multidisciplinary discussion and evaluated a range of pathologic features. Patchy fibrosis was found in 65/83 (78%) biopsies from FHP and 32/38 (84%) biopsies from UIP/IPF cases.
Fibroblast foci were present in 47/83 (57%) FHP and 27/38 (71%) UIP/IPF cases. Fibroblast foci/patchy fibrosis combined did not favor either diagnosis.
Architectural distortion was seen in 54/83 (65%) FHP and 32/38 (84%) UIP/IPF cases (odds ratio (OR) for FHP 0.35, p=0.036) and honeycombing in 18/83 (22%) and17/38 (45%) respectively (OR 0.37, p=0.014). Airspace giant cells/granulomas were present in 13/83 (20%) FHP and 1/38 (2.6%) UIP/IPF cases (OR for FHP 6.87, p=0.068), and interstitial giant cells/granulomas in 20/83 (24%) FHP and 0/38 (0%) UIP/IPF (OR 6.7x10(6), p=0.000).
We conclude that patchy fibrosis plus fibroblast foci can be found in TBCB from both FHP and UIP/IPF. The complete absence of architectural distortion/honeycombing favors a diagnosis of FHP as does the presence of airspace or interstitial giant cells/granulomas, but these measures are insensitive, and many cases of FHP cannot be separated from UIP/IPF on TBCB.