Osteomalacia: A Challenging Diagnosis Adverse Event Associated with Intravenous Ferric Carboxymaltose—A Case Report

Hypophosphatemia resulting from intravenous iron treatment has become an increasingly concerning syndrome in recent years. We report the case of a 66-year-old male patient with a medical history of ankylosing spondylitis (AS), Crohn’s disease, and chronic iron deficiency. Following intravenous iron infusions of ferric carboxymaltose, the patient developed diffuse bone pain and multiple bone fractures. After ruling out that the pain was in the context of spondyloarthritis (SpA), the diagnosis of osteomalacia associated with hypophosphatemia was established based on his clinical history, complementary analytical, and imaging tests. Once the diagnosis was made, intravenous ferric carboxymaltose infusions were discontinued, and oral calcium and vitamin D supplementation were initiated, resulting in clinical improvement with serum phosphate levels’ normalization. This case shows the importance of recognizing the risk factors and clinical findings in selected patients, monitoring phosphate levels in those with high risk factors and considering stopping or switching to another intravenous iron formulation. Furthermore, this case highlights the importance of maintaining clinical suspicion of other possible etiologies of pain in patients with SpA.