RANKL and cathepsin K in diffuse sclerosing osteomyelitis of the mandible

Background: Diffuse sclerosing osteomyelitis (DSO) of the mandible is characterized by mixed bone resorption and formation. Methods: Immunohistopathology of DSO in the clinically acute and subacute phases was compared with healthy bone. Results: Receptor activator of nuclear factor kappa B ligand (RANKL) was found in DSO lesions. When it was used in vitro to stimulate monocytes, cathepsin K expression was observed in mononuclear prefusion precursors and in multinuclear giant cells. Similarly, exacerbations of DSO were characterized by RANKL and induction of cathepsin K in mononuclear precursor cells, which subsequently seem to differentiate into osteoclasts or foreign body giant cells. The proportion of bone to soft tissue increased with the duration of disease. Conclusions: RANKL-driven osteoclastogenesis and acidic cysteine endoproteinase cathepsin K seem to play important roles in DSO as osteoclast-mediated bone resorption may represent the primary disease process later followed by new bone formation.