Granulomatous Interstitial Nephritis Suspected to Be Caused by Adverse Reaction to Metal Debris: A Case Report

Introduction: Adverse reaction to metal debris (ARMD) is a rare complication of metal-on-metal (MoM) joint prostheses, typically presenting as a localized immune response to metallic wear particles. Systemic manifestations, including nephropathy, are exceedingly rare. Granulomatous interstitial nephritis (GIN) induced by ARMD is particularly uncommon, and distinguishing it from systemic granulomatous diseases such as sarcoidosis poses a diagnostic challenge. We present a case of GIN suspected to be associated with cobalt-induced ARMD. Case Description: A 71-year-old man with a history of right total hip arthroplasty 16 years earlier presented with anorexia and progressive renal dysfunction, with serum creatinine (sCr) rising from 0.66 to 1.82 mg/dL over one year. Two months later, at referral, his sCr had further increased to 4.31 mg/dL, with corrected calcium of 14.0 mg/dL and CRP of 4.19 mg/dL. Physical examination revealed right inguinal lymphadenopathy. CT showed multiple enlarged lymph nodes and fluid accumulation in the right inguinal region and along the external iliac vein, without other lymphadenopathy. Lymph node biopsy revealed non-caseating granulomas. Lab tests showed elevated 1,25-dihydroxyvitamin D (143 pg/mL), ACE (52.8 IU/L), and cobalt (2.8 ng/mL; normal <1 ng/mL). Despite IV fluids, renal dysfunction persisted. Kidney biopsy revealed granulomatous interstitial nephritis. No systemic findings suggested sarcoidosis. Steroid therapy (prednisolone 0.8 mg/kg) led to rapid improvement: sCr dropped to 1.32 mg/dL, calcium normalized, and lymphadenopathy regressed. Based on clinical, radiologic, and pathologic findings, GIN secondary to ARMD was suspected. Revision surgery for the MoM prosthesis is planned. Discussion: GIN is a rare renal manifestation of ARMD that can mimic sarcoidosis due to overlapping histologic and biochemical features. In this case, the absence of systemic involvement, elevated cobalt levels, and history of MoM prosthesis support ARMD as the likely cause. Since cobalt is renally excreted, local accumulation may have triggered granulomatous kidney inflammation. Early recognition of ARMD can guide management, including prosthesis revision, and help avoid unnecessary long-term immunosuppression.