| Summary: | Immunoglobulin (Ig) G4-related disease is a recently described syndrome characterized by mass forming lymphoplasmacytic tissue infiltration and elevated serum IgG4 concentrations usually affecting middle-aged or older individuals. Lymphadenopathy is frequently observed and is sometimes the first or only manifestation of the disease. We report a case of IgG4-related disease mimicking Hodgkin lymphoma in a 13-year-old girl. The patient presented with progressive unilateral cervical lymphadenopathy of several months duration. Biopsy showed follicular hyperplasia with progressive transformation of germinal centers. Interfollicular areas were expanded by small lymphocytes, histiocytes, eosinophils and fibrosis with occasional CD30 positive cells initially concerning for interfollicular Hodgkin lymphoma. Immunohistochemical analysis revealed an intrafollicular plasmacytosis with an IgG4-positive/IgG-positive plasma cell ratio of 50% supporting a diagnosis of IgG4-related lymphadenopathy, progressively transformed germinal centers type. Laboratory studies were supportive with elevated serum IgG4 (178 mg/dL) and IgE (30.40 kU/L) levels along with an elevated serum IgG4/IgG ratio (0.16). Very few cases of IgG4-related disease have been described in children. Within this age group, there is considerable clinical overlap between IgG4-related disease associated lymphadenopathy and Hodgkin lymphoma. In addition, lymphadenopathy secondary to IgG4-related disease demonstrates substantial histologic diversity with the potential to simulate the inflammatory background and fibrosis of Hodgkin lymphoma. The importance of accurate diagnosis is underscored by the prognostic implications considering the marked response of the syndrome to steroid therapy. In addition, appropriate follow up is critical to monitor for relapse and additional organ involvement.
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