[Hypophosphatemic osteomalacia caused by urinary mesenchymal tumor: A case report]

This case report concerns a 34-year-old woman who had been diagnosed with ankylosing spondylitis (AS), fibromyalgia syndrome (FMS), osteoarthritis (OA), lumbar disc herniation and the like in different hospitals during the past 18 months. She had progressive osteoarthrosis, significant muscle weakness, gait abnormalities in weightbearing areas, however without typical inflammatory low back pain, while the treatment with non-steroidal anti-inflammatory drugs (NSAIDs) was invalid, with normal inflammation index, negative results for rheumatic factor (RF) and human leukocyte antigen (HLA)-B27, and normal erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). She had hyphosphatemia, normal serum calcium, 1,25-(OH)2-D3 reduction, elevated alkaline phosphatase (ALP) and normal parathyroid hormone (PTH), however with elevated urinary phosphorus. Finally, the medial thigh nodule was found in the subcutaneous of her inner leg by careful examination and imaging scans including B-ultrasound and PET/CT. The final pathology confirmed that the nodule was phosphate urinary mesenchymal tumors. After the tumor was removed, the patient was treated with anti-osteoporosis and phosphorus supplementation. The symptoms of bone pain and muscle weakness were alleviated, and hypophosphatemia was corrected. It was confirmed that the patient had low-phosphorus osteomalacia due to tumor. Tumor-induced hypophosphatemia osteomalacia (TIO) was a rare paraneoplastic syndrome which was caused by excessive phosphorus excretion induced by the tumor, and was thus categorized as an acquired hypophosphatemic osteomalacia. TIO had an occult onset and was associated with a high rate of misdiagnosis, although TIO has some typical clinical features. Early diagnosis, correctly positioning of the tumor, and surgical resection can achieve good outcomes.