To report a clinical case of tumor-induced hypophosphorus osteomalacia ( TIO ) ，and to improve clinicians’understanding of the disease

The clinical manifestations，laboratory，imaging，pathological and treatment follow-up of a TIO patient were analyzed and summarized．

A middle-aged male has been suffering from progressive bone pain for two years, significantly affecting his daily life. He has repeatedly sought outpatient and inpatient care dozens of times, with diagnoses including cervical and lumbar disc herniation, piriformis syndrome, and sciatica. Treatments such as cervical spine surgery, rehabilitation therapy, and neurotrophic therapy were administered, but his symptoms showed no improvement. Multiple tests revealed decreased blood phosphorus levels, elevated alkaline phosphatase, severe osteoporosis, and bilateral femoral head necrosis. A mass was also discovered in the anterior right tibia, but it was not given adequate attention and remained untreated. Over the two-year course of the illness, the patient experienced a reduction in both height and weight. There is no family history of similar diseases. Physical examination revealed that the patient could barely walk with crutches due to pain, and prolonged standing caused unbearable pain in both lower limbs. 

The patient was referred to our hospital through a multidisciplinary team (MDT) outpatient consultation and was admitted. Blood tests confirmed low phosphorus levels and elevated alkaline phosphatase, leading to a consideration of hypophosphatemic osteomalacia. A whole-body PET-CT scan with octreotide imaging revealed an irregular low-density shadow in the anterior right tibial muscle space with high OC uptake, suggesting a tumor. Further MRI of the right lower limb indicated a mass within the anterior tibial muscle.

This case supported the diagnosis of adult hypophosphorus osteomalacia and the right lower limb mass was removed by surgical operation．The pathological diagnosis accorded with phosphaturic mesenchymal tumor．After operation，the levels of blood phosphorus returned to normal quickly and ALP decreased．The patient was treated with appropriate calcium and vitamin D preparations．The pain was partially relieved．At the one-month follow-up, the patient reported mild relief of bone pain, with blood phosphorus levels at the lower limit of normal and alkaline phosphatase remaining slightly levated. 

An adult patient with hypophosphatemic osteomalacia without family history should be suspected as tumor-induced osteomalacia． Surgical resection of the tumor is the first of choice of treatment．