AIM: Transbronchial cryobiopsies are increasingly used for the diagnosis of interstitial lung disease (ILD), but there is a lack of published information on the features of specific ILD in cryobiopsies. Here we attempt to provide pathological guidelines for separating usual interstitial pneumonia (UIP) of idiopathic pulmonary fibrosis (IPF), fibrotic hypersensitivity pneumonitis (FHP) and connective tissue disease-associated ILD (CTD-ILD) in cryobiopsies. METHODS: We examined 120 cryobiopsies from patients with multidisciplinary discussion (MDD)-established CTD-ILD and compared them to a prior series of 121 biopsies from patients with MDD-established IPF or FHP. RESULTS: A non-specific interstitial pneumonia (NSIP) pattern alone was seen in 36 of 120 (30%) CTD-ILD, three of 83 (3.6%) FHP and two of 38 (5.2%) IPF cases, statistically favouring a diagnosis of CTD-ILD. The combination of NSIP + OP was present in 29 of 120 (24%) CTD-ILD, two of 83 (2.4%) FHP and none of 38 (0%) IPF cases, favouring a diagnosis of CTD-ILD. A UIP pattern, defined as fibroblast foci plus any of patchy old fibrosis/fibrosis with architectural distortion/honeycombing, was identified in 28 of 120 (23%) CTD-ILD, 45 of 83 (54%) FHP and 27 of 38 (71%) IPF cases and supported a diagnosis of FHP or IPF. The number of lymphoid aggregates/mm2 and fibroblast foci/mm2 was not different in IPF, CTD-ILD or FHP cases with a UIP pattern. Interstitial giant cells supported a diagnosis of FHP or CTD-ILD over IPF, but were infrequent. CONCLUSIONS: In the correct clinical/radiological context the pathological findings of NSIP, and particularly NSIP plus OP, favour a diagnosis of CTD-ILD in a cryobiopsy, but CTD-ILD with a UIP pattern, FHP with a UIP pattern and IPF generally cannot be distinguished.

Carolinas Pathology Group Atrium Health System Gainesville FL USA

Department of Laboratory Medicine and Pathology Mayo Clinic Phoenix AZ USA

Department of Medicine Division of Pulmonary Medicine Mayo Clinic Phoenix AZ USA

Department of Pathology and Molecular Medicine 3rd Faculty of Medicine of Charles University and Thomayer University Hospital Prague Czech Republic

Department of Pathology Immunology and Laboratory Medicine University of Florida Gainesville FL USA

Department of Pathology St Paul's Hospital University of British Columbia Vancouver BC Canada

Department of Pathology University of British Columbia and Vancouver General Hospital Vancouver BC Canada

Department of Respiratory Medicine 1st Faculty of Medicine of Charles University and Thomayer University Hospital Prague Czech Republic

Division of Pulmonary Critical Care and Sleep Medicine University of Florida Gainesville FL USA

GB Morgagni Hospital and DIMEC University of Bologna Forli Bologna Forli Italy

The Fingerland Department of Pathology Faculty of Medicine in Hradec Králové and University Hospital Hradec Kralove Charles University Hradec Králové Czech Republic

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