Hypophosphatemic osteomalacia induced by intravenous iron therapy: a case report

Abstract

Objective: Osteomalacia is an uncommon, overlooked and debilitating metabolic bone disease with numerous aetiologies. Herein, we report an atypical cause of osteomalacia - intravenous iron therapy.

Methods: Description of a case report of hypophophatemic osteomalacia induced by ferric carboxymaltose infusions.

Results: A 70-year-old male with Rendu-Osler-Weber syndrome requiring repeated infusions of ferric carboxymaltose was admitted for disabling lower limb pain associated with persistent hypophosphatemia (1.6mg/dL) and increased urinary fractional excretion of phosphate (43%, UP04=118.3mg/dL), serum fibroblast growth factor 23 (324UA/mL), intact parathyroid hormone (110pg/mL) and bone alkaline phosphatase (40.1mcg/L). X-ray and CT of the feet showed severe diffuse bone demineralization. Feet MRI displayed a subchondral fracture of the cuneiform-navicular joints. Spine X-ray revealed dorsolumbar vertebral flattening. Somatostatin receptor PET scan excluded an occult tumor. Bone biopsy with histomorphometry confirmed the presence of osteomalacia. After excluding other causes, a diagnosis of hypophosphatemic osteomalacia induced by frequent ferric carboxymaltose infusions was made. The iron formulation was replaced by saccharated ferric oxide infusions and progressive titration of calcitriol up to 1.5mg/day and oral disodium phosphate up to 5740mg/day was started. After 6 months, there was a clear clinical and analytical improvement.

Conclusion: Osteomalacia may be a consequence of prolonged hypophosphatemia induced by recurrent ferric infusions, which is an uncommon and neglected bone adverse event of this therapy. Phosphate levels and bone symptoms should be monitored during repetitive iron infusions, maintaining a high level of suspicion for osteomalacia as it is important to identify and treat it in a timely manner, minimizing its severe morbidity.

Keywords: Ferric carboxymaltose; Osteomalacia; Rendu-Osler-Weber disease.