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.