O29 Keeping a watchful eye: IgG4-positive lymphoma masquerading as IgG4-related ocular disease

Abstract Case report - Introduction IgG4-related disease (IgG4-RD) is increasingly recognised in rheumatology practice. We describe a case of orbital swelling initially diagnosed as IgG4-RD. It was exquisitely steroid responsive and she was treated with 6 years of immunosuppression but her symptoms later deteriorated. She developed worsening left eye swelling that required debulking surgery; histopathology demonstrated IgG4-positive lymphoma. She had an excellent response to localised radiotherapy and remains in remission. Although her initial presentation was typical of IgG4-RD, her subsequent lack of response to steroids prompted reconsideration of the initial diagnosis and re-examination of her previous biopsy specimen, confirming IgG4-positive Iymphoma at both timepoints. Case report - Case description A 25-year-old lady presented in 2008 with a swollen left eye. She had a history of childhood eczema, asthma and sinusitis. Diagnostic excision was undertaken; histology was considered to show chronic inflammation, scattered eosinophils, dense fibrosis and no granulomas. She was diagnosed with a ‘granulomatosis with polyangiitis-like’ orbital pseudotumour. It was exquisitely steroid responsive; mycophenolate mofetil was added from an early stage of treatment. The patient was referred to rheumatology 3 years after diagnosis as she was unable to reduce her prednisolone below 5mg daily. Her immunology screen was negative. Although her plasma IgG4 levels were normal at 0.14g/L, the original histology was reviewed and immunostained for IgG4. This demonstrated more than 80% of plasma cells to be IgG4 positive, with the previously noted dense fibrosis and chronic inflammatory infiltrate. Her diagnosis was revised to orbital IgG4-RD. She commenced azathioprine as she was planning a pregnancy. Following an uncomplicated pregnancy in 2014, her symptoms significantly deteriorated, with worsening pain, discharge and swelling in her left eye. A repeat MRI scan showed a new cuff of abnormal tissue within the lateral aspect of the left orbit. She was referred to ophthalmology and underwent left anterior orbitotomy with debulking. Histopathology at this time was consistent with extranodal marginal zone lymphoma (EMZL) of MALT (mucosa-associated lymphoid tissue) type, IgG4 positive. An extraordinary feature was an abundance of crystal-storing histiocytes, presumed to contain ingested IgG4. To investigate whether she had an IgG4-secreting lymphoma from the beginning or whe