HARDER TO BREATHE: AN UNSUAL CASE OF SEVERE HYPERPHOSPHATURIC HYPOPHOSPHATEMIA AND NORMAL FGF-23 LEVELS IN A YOUNG FEMALE PATIENT

George Vasquez Rios, M.D.1, Eric Marin, M.D.2, Kevin Martin, M.D.3, Adam Merando, M.D.4, 1Department of Internal Medicine, School of Medicine, Saint Louis University, Saint Louis, Missouri, USA, Saint Louis, MO; 2Department of Internal Medicine, School of Medicine, Saint Louis University, Saint Louis, Missouri, USA; 3Nephrology Division, Department of Internal Medicine, Saint Louis University, Missouri, USA; 4Department of Internal Medicine, School of Medicine, Saint Louis University, Saint Louis, Missouri, USA, St. Louis, MO

Meeting: Hospital Medicine 2018; April 8-11; Orlando, Fla.

Abstract number: 899

Categories: Adult, Clinical Vignettes, Hospital Medicine 2018

Keywords: , ,

Case Presentation: A 33-year-old Caucasian woman presented with increasing fatigue, palpitations and shortness of breath for the previous three weeks. She had a history of iron deficiency anemia, gluten sensitivity, and compensated anorexia. One month prior to admission, she received two doses of intravenous ferric carboxymaltose (FCM) supplementation. Upon evaluation, vitals were BP: 134/69 mmHg, HR: 74 bpm, RR: 18 rpm (SaO2: 98%), T: 37 C. Physical examination revealed mild muscle tenderness in the thighs, but otherwise unremarkable.

Discussion: Laboratory findings were relevant for severe hypophosphatemia (serum phosphorus: 1.2mg/dL), sCa: 8.8 mg/dL and alkaline phosphatase: 88 IU/L. Additional studies revealed PTH: 38.7 pg/mL, 25(OH) vitD: 22.0 ng/mL, c-terminal FGF-23: 116 RU/mL (ref: 44 – 215 RU/mL) and TSH: 1.8 uIU/mL. CBC, basic chemistry, hepatic function panel and iron studies were all within normal limits. She was found to have hyperphosphaturia (fractional excretion of PO4-3: 99.76%). Despite intensive replacement with both intravenous phosphorus (90 mmol/L/day) and oral phosphorus (32 mmol/L/day), her serum levels remained critical, dropping as low as 0.7 mg/dL and associated with increased respiratory symptoms. Due to concerns of FCM-induced Na/PO4-3 co-transporter dysfunction, we attempted to replete her calcitriol deposits by prescribing intravenous calcitriol (1 mcg/day) with slow titration up to 3 mcg/day. After two weeks of treatment with high dose calcitriol, her serum phosphorus levels were noted to rise back within normal limits. During follow-up, the patient was noticed to be in good health with a phosphorus level at 4 mg/dL.

Conclusions: Ferric carboxymaltose is an emerging cause of transient severe hypophosphatemia in hospital medicine, which can result in death if not appropriately addressed. Our case highlights the importance of a physiology-driven approach to treating hypophosphatemia including the use of innovative therapies such as calcitriol repletion.

To cite this abstract:

Vasquez Rios, G; Marin, E; Martin, K; Merando, A. HARDER TO BREATHE: AN UNSUAL CASE OF SEVERE HYPERPHOSPHATURIC HYPOPHOSPHATEMIA AND NORMAL FGF-23 LEVELS IN A YOUNG FEMALE PATIENT. Abstract published at Hospital Medicine 2018; April 8-11; Orlando, Fla. Abstract 899. https://www.shmabstracts.com/abstract/harder-to-breathe-an-unsual-case-of-severe-hyperphosphaturic-hypophosphatemia-and-normal-fgf-23-levels-in-a-young-female-patient/. Accessed November 14, 2019.

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