Abstract: FR-PO1280
The Vanishing Phosphate: Severe Renal Phosphate Wasting After Dexamethasone in Central Nervous Syndrome (CNS) Lymphoma
Session Information
- Onconephrology: Diagnostic Dilemmas, Therapy-Related Toxicities, and Clinical Cases
October 23, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Onconephrology
- 1600 Onconephrology
Authors
- Joseph, Thomas, Loyola Medicine, Maywood, Illinois, United States
- Iftikhar, Muhammad Ali, Loyola Medicine, Maywood, Illinois, United States
- Barnes IV, Sylvester, Loyola Medicine, Maywood, Illinois, United States
Introduction
Hypophosphatemia in oncology patients is often multifactorial and may result from decreased intake , intracellular shifts, or renal losses. Glucocorticoids are an underrecognized cause of renal phosphate wasting and can significantly disrupt mineral metabolism.
Case Description
72 year old female with diabetes , hypertension , high grade B Cell lymphoma with CNS involvement receiving high dose intravenous dexamethasone and methotrexate presented with lethargy. Laboratory evaluation revealed profound hypophosphatemia(serum phosphorus <1.0mg/dl) Random urine phosphorus(27mg/dl) with urine creatininne(16mg/dl) was inappropriately elevated in the setting of severe hypophosphatemia consistent with renal phosphate wasting.
Discussion
The hypophosphatemia was determined to be multifactorial, with high dose dexamethasone as the primary driver. Glucocorticoids promote proximal tubular phosphate wasting and inhibit renal 1-alpha hydroxylase, reducing calcitriol synthesis and imparing intestinal phosphate absorption . The patient demonstrated inappropriately normal baseline parathyroid hormone level in the setting of profound hypophosphatemia , followed by transient elevation , reflecting dynamic calcium-phosphate shifts. Concomitant hypocalcemia and poor oral intake further exacerbated phosphate depletion. Adjustment of steroid therapy and supportive management, including calcitriol supplementation, were associated with improvement. High dose dexamethasone can cause clinically significant renal phosphate wasting and severe hypophosphatemia in oncology patients. Recognition of this mechanism is critical to ensure timely diagnosis and apporpriate managment,particularly in complex clinical settings.