A masquerading mass: an unusual presentation of IgG4-related systemic disease with tubulointerstitial nephritis.

IgG4 tubulointerstitial nephritis (IgG4-TIN) is the most common form of IgG4 renal disease. When IgG4-TIN is accompanied by other systemic manifestations the disease is known as IgG4-related systemic disease (IgG4-RSD). IgG4-RSD is well recognised in the form of tubulointerstitial nephritis (IgG4-related TIN) and may present with renal failure by mimicking neoplasms (tumefactive lesions) or with both features. We describe a case of IgG4-RSD initially presenting as a submandibular mass and subsequently presenting two years later with secondary infiltration of the kidney causing tubulointerstitial nephritis. This case highlights the importance of recognising IgG4-RSD as a non-malignant disease with presentations having commonly shared features including tumour-like swelling of involved organs and its ability to mimic many systemic diseases. In the majority of patients it can be treated successfully with corticosteroids.