IgG-related disease: an atypical presentation of steroid-responsive renal mass.

IgG-related disease (IgG-RD) is a systemic fibroinflammatory disease characterised by dense lymphoplasmacytic infiltration rich in IgG-positive plasma cells, storiform fibrosis and obliterative phlebitis. Serum IgG levels are typically elevated but half of the patients had normal serum IgG levels. IgG-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 IgG-RD has been reported. Thus, differentiating malignancy from IgG-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 IgG-RD with renal mass in a young man that resolved with glucocorticoid therapy alone.