Introduction:
Co-presentation of perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) and anti-glomerular basement membrane (anti-GBM) antibodies is considered relatively rare. Anti-GBM disease and ANCA-associated vasculitis (AAV) both can present with life-threatening manifestations such as rapidly progressive glomerulonephritis and alveolar haemorrhage. Studies of double-positive cohorts suggest a hybrid phenotype, combining features of AAV – such as older age at presentation, longer prodromal symptoms, chronic histologic changes, and a tendency to relapse – with the severe renal involvement and frequent pulmonary hemorrhage typical of anti-GBM disease.

Case description:
An 82-year-old woman with a history of arterial hypertension, chronic heart failure, asthma, anaemia, and bronchiectasis was admitted to the nephrology unit in July 2025 due to deterioration of her general condition and rapidly progressing chronic kidney disease. Renal function had been normal in June 2024; however, elevated renal parameters were first documented in January 2025. On admission, laboratory tests revealed serum creatinine 4.2 mg/dl and estimated glomerular filtration rate (eGFR) of 10 ml/min/1.73 m², proteinuria, elevated inflammatory markers and positivity for p-ANCA and anti-GBM antibodies. Immunofixation electrophoresis was unremarkable. Imaging studies demonstrated interstitial lung disease and sinonasal polyps. In early August, the patient received three intravenous pulses of methylprednisolone (250 mg each), followed by oral prednisone 40 mg daily. She subsequently underwent four sessions of plasmapheresis until anti-GBM antibody negativity was achieved. Remission-induction therapy with cyclophosphamide was initiated; after eight pulses, until January 2026, serum creatinine decreased to 3 mg/dl, and eGFR increased to 15 ml/min/1.73 m².

Conclusions:
This case shows that despite presenting with advanced chronic renal disease, this double-positive patient may recover renal function after aggressive therapy. These observations highlight the importance of early intensive diagnostics and treatment, including plasma exchange and immunosuppression, followed by careful long-term monitoring and consideration of maintenance immunosuppressive therapy.