A "Blistering" Case of Primary FSGS When Skin and Kidneys Collide

Introduction: While both FSGS and BP are independently well-described, their co-occurrence is exceedingly rare. Associations between autoimmune blistering diseases and glomerular pathologies, most commonly membranous nephropathy, suggest potential immune dysregulation or antigenic mimicry. We presents a case of simultaneous primary FSGS and bullous pemphigoid, exploring possible immunopathogenic links and clinical implications Case Description: 65-year-old female with hypertension, initially presented in 10/2020 with proteinuria on routine testing, normal kidney function, and slightly reduced albumin. Serologic workup was unremarkable. Biopsy showed mild glomerular ischemic changes, negative IF, and EM findings of extensive foot process effacement consistent with minimal change disease. No monoclonal deposits or amyloidosis were identified. She was treated with prednisone and achieved remission. patient reported allergy to Bactrim and had intermittent skin lesions evaluated by dermatology In 5/2022, had worsening proteinuria 7.8g, albumin 2.8 g/dl, and creatinine 0.8 mg/dl. Repeat biopsy and clinical presentation consistent with primary FSGS. Tacrolimus was initiated, leading to significant improvement. It was gradually weaned and discontinued. However, in 2024 relapsed again, and treated with Tacrolimus. Rituximab offered, however, patient refused In 2/2025, she developed blistering skin lesions and oral mucosa fragility. Dermatologic evaluation revealed positive BP180 IgG, negative BP230 IgG, and biopsy confirmed bullous pemphigoid. Treatment included a steroid taper and initiation of mycophenolate 500 mg BID, with plans to wean off tacrolimus Discussion: Both FSGS and BP involve immune dysregulation—FSGS via circulating permeability factors or T-cell-mediated injury, and BP via autoantibody-mediated complement activation at the basement membrane. A potential unifying mechanism could involve cross-reactivity of autoantibodies affecting both glomerular and dermoepidermal membranes The dual presence also raises the possibility of a broader systemic autoimmune process or a paraneoplastic syndrome, although no definitive link has been established. Recognizing such presentations is crucial, as a unifying treatment strategy might be possible. AS nephrologists, we need to be more proactive about skin lesions and evaluation in autoimmunity