A clue in the toe: Unveiling the sinister diagnosis

ABSTRACT We present the case of a young adult female who developed multiple fragility fractures, starting with the left femoral neck and later the right hip, along with persistent musculoskeletal pain and proximal muscle weakness. Initial treatment with calcium and cholecalciferol had ineffective results. Laboratory findings indicated severe hypophosphatemia, elevated alkaline phosphatase, normal calcium and parathyroid hormone levels, and a low tubular maximum for phosphate reabsorption, indicating renal phosphate wasting. Elevated fibroblast growth factor 23 (FGF23) levels suggested an FGF23-secreting tumor, localized via imaging to the right great toe. The patient was treated with phosphate, elemental calcium, and 1,25-dihydroxy vitamin D supplementation. Following surgical excision of the tumor, her phosphate and FGF23 levels normalized. Three months post-surgery, she showed significant improvement in mobility and pain reduction. This case underscores the importance of considering tumor-induced osteomalacia in patients with unexplained fractures and persistent musculoskeletal symptoms.