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IgG IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disease characterised by dense lymphoplasmacytic infiltration rich in IgG4-positive plasma cells, storiform fibrosis and obliterative phlebitis. Serum IgG4 levels are typically elevated but half of the patients had normal serum IgG4 levels. IgG4-RD represents a spectrum of diseases that involve various organs such as the pancreas, liver, kidneys, and salivary glands often manifesting as diffuse organ enlargement or a mass-like lesion mimicking cancer. An increased incidence of malignancy among patients with IgG4-RD has been reported. Thus, differentiating malignancy from IgG4-RD manifestation is important as the treatment differs. Glucocorticoids are considered first-line therapy and should be started early to prevent fibrosis. Patients usually have an excellent clinical response to steroids, and poor steroid response is indicative of an alternative diagnoses such as malignancy. This case report describes a case of IgG4-RD with renal mass in a young man that resolved with glucocorticoid therapy alone.

IgG IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder affecting multiple organ systems. The awareness of this disease has tremendously increased over the last decade leading to effective treatment and decreased morbidity to the patients. Histopathology plays an important role in the diagnosis of IgG4-RD, and definite histologic criteria are proposed in clinically suspected patients. We report a patient with multiple organ system involvements of the salivary gland, lymph node and kidney. IgG4-related lymphadenopathy (IgG4-RL) in this patient was misdiagnosed as nodular lymphocyte predominant Hodgkin's lymphoma (NLPHL). Refractoriness to treatment for NLPHL and subsequent manifestations of renal involvement lead us to the correct diagnosis of this potentially treatable condition. IgG4-RL can mimic reactive proliferation as well as lymphomas. We report the clinical presentation and discuss the problems faced by pathologists in diagnosing IgG4-RL. We believe that awareness of this rare presentation will enhance the knowledge in diagnosing IgG4-RD.