[IgG4-associated disease in differential diagnosis of inflammatory orbitopathy]

IgG4-associated disease (IgG4-RD) is a systemic inflammatory disease characterized by tumorlike sclerosing masses in different organs. Differential diagnosis in orbital IgG4-RD includes majority of conditions, such as thyroid eye disease (TED), sarcoidosis, granulomatosis with polyangiitis, idiopatic orbital inflammation, limphoproliferative diseases and others. A case of IgG4-RD with different organs involvement and complicated differential diagnosis is presented. This case demonstrates very uncommon manifestation of IgG4-RD, when orbital involvement was very similar with TED. Systemic process was not recognized during a long period of time and diagnosis of IgG4-RD was established only after biopsy of abnormally increased lacrimal gland. Differential diagnosis included other systemic diseases, first of all sarcoidosis, GPA, and lymphoma. Biopsy results were consistent with the gold standard of diagnosis, e. g. more than 40% of plasma cells were IgG4 positive. This case demonstrates the necessity of orbital biopsy before starting immunosuppression to avoid inappropriate treatment strategy.