Xanthogranulomatous osteomyelitis (XO) is a peculiar aspect of osteomyelitis characterized by prevalent histiocytic infiltrate and foamy macrophage clustering.
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Clinical picture
As of 2011 five cases had been reported, involving rib, tibial epiphysis, ulna, distal tibia and femur. Young individuals are prevalently affected but one case involved a 50-year-old woman. Pain, swelling of possibly long duration, fever and increased ESR are some of the main clinical findings. X-ray examination shows lytic foci with sclerotic margins. A neoplastic process can be suspected.
Pathology
The granulomatous tissue largely comprises foam cells of monocyte/macrophage origin positive for KP1, HAM56, CD11b and CD68. Neutrophils, hemorrhagic foci and numerous plasma cells are additional findings. Staphylococcus aureus was isolated in the case reported by Kamat et al. A delayed type hypersensitivity reaction in cell-mediated immunity has been suggested in this type of infiltrate that is composed of macrophages and T cells. T cells are represented by a mixture of CD4+ and CD8+ lymphocytes. Macrophages and lymphocytes show marked expression of HLA-DR antigen. Arguably XO is the bone localization of the xanthogranulomatous process occurring in several other locations.