Severe hypophosphatemia following ferric carboxymaltose in a patient presenting with a focal seizure: a case report

Background

Ferric carboxymaltose can cause fibroblast growth factor 23-mediated renal phosphate wasting; neurological presentations may delay recognition. Case Presentation: A 76-year-old woman presented after a 2-minute focal seizure one month after receiving a single 1 g intravenous ferric carboxymaltose infusion for iron-deficiency anemia. Computed tomography of the head and electroencephalography showed no acute intracranial or epileptiform cause. Extended testing demonstrated severe hypophosphatemia (0.23 mmol/L) and hypomagnesemia (0.52 mmol/L), with recurrent phosphate decline despite replacement. Fibroblast growth factor 23 was inappropriately normal (35 pg/mL) for the preceding severe hypophosphatemia, supporting ferric carboxymaltose-associated phosphate wasting. Concurrent pantoprazole use likely contributed to hypomagnesemia. After phosphate and magnesium replacement and pantoprazole discontinuation, electrolytes stabilized by day 12 and no further seizure occurred.