Immune Complex-Mediated Membranoproliferative Glomerulonephritis Mimicking ANCA: Kidney Involvement in a Patient with Sjogren Syndrome and Antiphospholipid Syndrome Without Histologic Evidence of Vasculitis

Introduction: Sjogren’s syndrome (SS) and antiphospholipid syndrome (APS) may sumultaneously occur but rarely present with overlapping renal involvement. Both conditions independently cause distinct kidney pathologies—immune complex glomerulonephritis in SS and thrombotic microangiopathy (TMA) in APS. We present a case in which misleading immunofluorescence mimicking ANCA vasculitis led to the diagnosis of this rare overlap. Case Description: A 69-year-old female with hypertension and remote breast cancer in remission presented with exertional dyspnea and bilateral lower extremity edema. Laboratory findings revealed nephrotic-range proteinuria (UPCR 16 g/day), hematuria, hypocomplementemia, and elevated serum creatinine and was initiated on hemodialysis. ANCA testing showed an atypical immunofluorescence pattern without clear correlation to c-ANCA or p-ANCA. Serologies revealed positive SSA/SSB and high-titer antiphospholipid antibodies (lupus anticoagulant, β2-glycoprotein I IgG, anticardiolipin IgG).Patient declined immunosuppressive therapy and continued to require hemodialysis.Kidney biopsy demonstrated immune complex–mediated membranoproliferative glomerulonephritis (MPGN) with no necrotizing lesions or crescents. Additional findings included acute tubular injury, focal chronic interstitial nephritis, and severe arteriosclerosis. There were no features of thrombotic microangiopathy. Of 43 glomeruli, 60% were globally sclerotic, with 35–40% interstitial fibrosis and tubular atrophy. Discussion: This case underscores the importance of histologic confirmation when atypical ANCA patterns are reported. In this overlap syndrome, SS likely contributed to immune-mediated injury while APS introduced thrombotic risk though TMA was not observed. Management of this patient required both immunologic and thrombotic sequelae.Overlapping autoimmune syndromes need to be recognized that they may mimic ANCA associated vasculitis under immunofluorescence studies. Kidney biopsy is of paramount importance for distinguishing immune-complex GN from vasculitis or thrombotic processes to guide effective therapy.