Double Trouble: A Rare Case of Cephalosporin-Induced Myeloperoxidase Glomerulonephritis with Acute Interstitial Nephritis

Introduction: Myeloperoxidase (MPO) glomerulonephritis and acute interstitial nephritis (AIN) are distinct pathological entities that have rarely been reported to occur concurrently. Case Description: A 76-year-old female with PMH HTN and HLD presented to the ED with worsening bilateral lower extremity edema and a non-pruritic rash which started on her arms and spread to the trunk, back and groin. Of note, she was hospitalized 12 days prior for a UTI and received ceftriaxone and later cefpodoxime. On exam, vitals were stable and she was afebrile; she had bilateral lower extremity pitting edema and a maculopapular rash on the upper extremities, torso, and groin. Labs revealed WBC 31.7, Hb 9.9, absolute eosinophil count 1.4, BUN 49, and Cr 3.5. She was admitted for acute kidney injury due to possible AIN given diffuse rash, elevated eosinophils, and recent cephalosporin use. Further studies revealed positive MPO-ANCA antibodies, negative PR3-ANCA antibodies, low C4, positive ANA, positive RF, and negative GBM. A subsequent renal biopsy demonstrated MPO-positive, pauci-immune type, subacute crescentic glomerulonephritis, active necrotizing vasculitis involving two small arteries and global glomerulosclerosis, and active interstitial inflammation. Her clinical condition improved with hemodialysis, steroids, and rituximab. Discussion: MPO glomerulonephritis is a form of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis, characterized by immune complex deposition and inflammation within the glomeruli [1]. AIN is an immune-mediated renal injury primarily affecting the renal interstitium, often induced by medications such as antibiotics [2]. To date, there have been four cases in medical literature reporting concurrent MPO glomerulonephritis and drug-induced AIN [3-6]. The pathophysiological mechanisms underlying this dual renal insult from cephalosporin use remain unclear but may involve a combination of immune-mediated processes and drug-induced hypersensitivity reactions. The simultaneous manifestation of both conditions poses diagnostic and therapeutic challenges that require further research regarding the optimal management strategy.