Tumor-Induced Osteomalacia Caused by a Phosphaturic Mesenchymal Tumor of the Sole Presenting as a Crippling Illness in a Postmenopausal Woman

Tumor-induced osteomalacia, a rare and intriguing paraneoplastic syndrome that is usually caused by a phosphaturic mesenchymal tumor, leads to severe pain and hypophosphatemia. However, during clinical practice, most patients suffer from significant delay of diagnosis and treatment because the symptoms are similar to those of some very common diseases, such as osteoporosis and osteoarthritis. Moreover, physical complaints from postmenopausal women usually exacerbate the possibility of such delays. We describe a case of a postmenopausal woman with crippling bone pain and weakness, who had been diagnosed with a case of simple osteoporosis and osteoarthritis for 3 years, even with fine-needle aspiration biopsy of the offending phosphaturic mesenchymal tumor. After surgical removal of the 2 × 3-cm² tumor in her sole, we observed immediate relief of her systemic symptoms, with visual analogue scale improvement from 5 of 10 preoperatively to 2 of 10 5 days after surgery. There were no signs of recurrence during 2-year follow-up. This case highlights the significance of thorough history-taking as a fundamental tool for diagnosis even in the era of advanced technology, and that the awareness of tumor-induced osteomalacia should be raised. Otherwise, such a small localized soft tissue mass would seldom be associated with the severe systemic symptoms.