X-linked Hypophosphatemia (XLH) Mimicking Rheumatic Disease

A 38-year-old woman, who had been genetically diagnosed with X-linked hypophosphatemia (XLH) in childhood, was referred to our hospital due to persistent back pain and bilateral heel pain. She had visited an orthopedic surgeon and had been treated with adalimumab under a diagnosis of ankylosing spondylitis. A detailed interview revealed that she had ceased taking phosphorus and vitamin D. An X-ray showed enthesopathy, ligament calcification (Picture A), ver-