Bone histomorphometric and immunohistological analysis for hyperostosis in a patient with SAPHO syndrome: A case report

A 56-year-old Japanese woman with a history of palmoplantar pustulosis was admitted for examination due to left femur pain. Radiography and computed tomography showed thickening of the bone on the outer portion of the left femur. Bone scintigraphy of the left femur showed intense radioactive uptake. Consequently, the patient was diagnosed with SAPHO syndrome. Bone histomorphometric analysis of the left femur showed cancellous bone with thickened cortical bone. Whilst normal bone shows cancellous bone with double labeling (normal turn over), and cortical bone with no labeling (low turn over, adynamic state), this case presented with both cancellous and cortical bone with marked double labeling (indicating high turn over), abundant osteoid and woven bone. Immunohistological analysis showed that cells lining the bone surface consisted of osteoblasts and were positive for alkaline phosphatase (ALP). Few to little of these cells were positive for tartrate-resistant acid phosphatase (TRAP)-5B, cathepsin K and matrix metallopeptidase 9 (MMP-9). These results indicate that, in this case study, excessive production of osteoblasts contributed to hyperostosis of the left femur, with abundant osteoid and woven bone. This type of bone formation in SAPHO syndrome is not lamellar bone seen in normal bone, but rather fragile and mechanically weak bone, resulting in bone pain. Doxycycline may be a therapeutic option for bone pain in this patient.