Hodgkin lymphoma mimicking the IgG4-related disease: A diagnostic pitfall

This is a diagnostically challenging case that concerns a 29-year-old man with an eight-year history of right-sided neck swelling. The magnetic resonance imaging (MRI) of the neck revealed multiple well-encapsulated, lobulated, matted right cervical lymphadenopathy. He reported significant weight loss, but denied shortness of breath, altered bowel habits, or bone pain. His initial investigations revealed a normocytic hypochromic anaemia, mild leukocytosis, and thrombocytosis. The initial histological findings showed many IgG4-positive plasma cells, but lacked stromal fibrosis, granuloma, obliterative phlebitis, or malignant cells. In addition, the IgG4+/IgG plasma cell ratio was only about 20%. The serum IgG4 subclass was raised at 258 mg/dl, along with a raised serum IgG1 subclass at 3630 mg/dl. His bone marrow aspirate findings showed reactive plasmacytosis without marrow infiltration or acute leukaemia. Multiple myeloma was excluded by the absence of paraproteins in the serum and urine electrophoresis. A working diagnosis of probable IgG4-RD was made, and he was treated with glucocorticoids and azathioprine. However, the neck mass did not resolve, and the serum globulin was persistently high, ranging from 75 g/l to 95 g/l. A repeat biopsy of the neck swelling demonstrated Hodgkin lymphoma (HL) with mixed cellularity, and the Epstein-Barr virus (EBV) RNA-in-situ hybridisation was negative. He was started on chemotherapy and achieved complete remission, with an episode of relapse 9 months later. Salvage chemotherapy was initiated and is currently awaiting haematopoietic stem cell transplantation. This case highlights the need for repeated histopathological evaluation and reflects the complexity and overlap between HL and IgG4-RD.