Fanconi syndrome secondary to deferasirox with severe and prolonged urinary potassium loss in a β-thalassemia major patient

Abstract

The patient is a 16-year-old female with β-thalassemia major treated with hematopoietic stem cell transplantation, having received deferasirox (Def) therapy for 3 years for transfusional iron overload. At the age of 13 years, she was started on Def. After 5 months, she was found to have hypokalemia, hypophosphatemia, and hypouricemia and required phosphate supplementation. At 16 years, she developed gastroenteritis. Laboratory data showed hypokalemia, hypophosphatemia, hypouricemia, glycosuria, and low-molecular weight proteinuria. She was diagnosed as Fanconi syndrome related to Def and required potassium supplementation in addition to phosphate. In spite of reducing the dose of Def, Fanconi syndrome worsened 4 months later, which necessitated the discontinuation of Def. While hypophosphatemia, hypouricemia, glycosuria, and low-molecular weight proteinuria resolved after 1 month, urinary potassium loss persisted. She needed potassium supplementation for 1 year. In addition to hypokalemia, natriuresis and polyuria, recognized subsequently, also persisted. Enhanced NaCl intake along with an aldosterone blocker helped to reduce urinary potassium loss. It was considered that hypokalemia was attributable to decreased proximal reabsorption of sodium, increased distal delivery, and aldosterone-driven sodium-potassium exchange leading to urinary potassium loss.