The Case ∣ A 42-year-old male with 3-year bone pain and a soft tissue mass

A 42-year-old man was referred for the evaluation of diffuse bone pain and newly found hypophosphatemia. He had progressive bone pain over the lower back, pelvis, and bilateral hips, muscle weakness and difficult ambulation since 3 years ago. Initially, he was diagnosed to have ankylosing spondylitis but failed to respond with non-steroidal anti-inflammatory drugs, etoxicomab and etanercept therapy. One month ago, he was admitted at orthopedic ward for L-spine compression fracture. Radiography revealed a Looser zone at right proximal femur. 99mTc-bone scintigraphy showed diffuse skeletal uptake including axial bone, ribs, and proximal femurs. The detailed searches including computed tomography of the chest and abdomen, immune disorders, and malignancy were unrevealing. The pertinent laboratory results are shown in Table 1. He was put on oral calcitriol 2 μg and phosphorous salt containing phosphate 2 g daily. Nevertheless, his hypophosphatemia persisted and diffuse bone pain was only partially alleviated.