Miositis proliferativa con metaplasia ósea. Reporte de un caso

An ill-defined, 2 × 1 cm whitish lesion was found in the deltoid muscle. A proliferation of spindle cells, pseudoganglion cells and calcified osteoid was observed. Immunohistochemistry showed positivity for vimentin, β-catenin (cytoplasmic), Ki 67 (6%) and focal positivity for actin and myosin smooth muscle in spindle cells, negativity for MYO-D1, myogenin, CD34, desmin, caldesmon. A diagnosis of proliferative myositis with foci of osseous metaplasia was made.