Type I Gaucher disease with severe skeletal destruction, extraosseous extension, and monoclonal gammopathy.

Extraosseous extensions of Gaucher-cell deposits simulate malignant diseases. We describe a 65-year-old male with type-I Gaucher disease, confirmed by low leukocyte glucocerebrosidase activity, high plasma chitotriosidase, and N370/L444P gene-mutations, who had severe skeletal involvement, IgG-kappa monoclonal gammopathy, and a soft-tissue mass within the left iliac muscle. Bone marrow biopsy showed heavy infiltration by Gaucher cells, and histopathology of the excised extraosseous mass revealed infiltration by Gaucher cells. Thus, malignant diseases were excluded and the diagnosis of an extraosseous Gaucher-cell extension was well documented. Our case is reported because it is very interesting and unique in the literature.