Fine needle aspiration cytology of IgG4‐related disease: A potential diagnostic pitfall?

Background IgG4‐related disease (IgG4‐RD) is a tumefactive fibro‐inflammatory lesion that can affect any organ system in the body. Till date, no cytological data on IgG4‐RD are available and this is the first study depicting the cytopathology features of IgG4‐RD. Aim and Objective To describe the cytopathological features and potential diagnostic errors of IgG4‐RD. Materials and Methods The cytological features of 10 histopathology proven IgG4‐RD cases (11 samples) were retrospectively reviewed along with corresponding histopathology. Results The cellularity of the cytology smears was low (36.4%) to moderate (45.4%) to high (18.1%). The low cellularity correlated well with the pattern C in histopathology (predominant fibrosis pattern). The non‐epithelial background showed a preponderance of lymphocytes along with polymorphs and spindle‐shaped fibroblasts. Most of these cases showed the presence of plasma cells and eosinophils. Epithelial atypia was seen in 18.2% cases. Conclusion The causes of misdiagnosis were low cellularity, epithelial atypia, and non‐representative background. The important diagnostic clues to suspect a diagnosis of IgG4‐RD include low cellularity despite adequate effort, inflammatory background rich in lymphocytes and spindle cells admixed with a few plasma cells and eosinophils along with radiological features and raised serum IgG4 Diagn. Cytopathol. 2017;45:14–21. © 2016 Wiley Periodicals, Inc.