Rheumatoid Nodule Formation in the Kidney: A Diagnosis of Exclusion and a Rare Manifestation of Rheumatoid Arthritis Involving the Kidney

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by an inflammatory polyarticular arthritis as well as extra-articular manifestations. Although renal involvement of the kidney by RA most often is expressed as an immune complex–mediated glomerulopathy or AA amyloidosis, rheumatoid nodule formation has been rarely described.1 A rheumatoid nodule is characterized by necrotizing granulomatous inflammation, and can be found most commonly subcutaneously in patients with RA over sites prone to pressure or repetitive irritation, but also have been described to involve the deeper connective tissue, lungs, heart, and other tissue sites.2 As the etiology of a necrotizing granuloma can be of an infectious process, this possibility must be excluded particularly for patients with RA. We present a case in which a patient with longstanding RA is found by radiologic imaging to have a kidney mass. Histopathologic review of the subsequent partial nephrectomy revealed a necrotizing granuloma and an immune complex–mediated glomerulopathy predominately with a membranous pattern of injury. After histopathologic, molecular, further laboratory, and clinical evaluation, it was felt that the necrotizing granuloma was not of an infectious etiology and represented a rheumatoid nodule.