Aggressive transformation of a quiescent primary bone lymphoma simulating Paget's disease.

Primary multifocal osseous lymphoma is a rare and poorly recognized entity. Here, we present an instructive case of a young man who, six years after a local contusion of the left ankle, developed a painful polylobulated large soft tissue mass. This mass turned out to have arisen from the transformation of a centro follicular non-Hodgkin's lymphoma into a diffuse large B-cell lymphoma involving the calcaneus, talus, cuboid and navicular bones. The diagnostic difficulties as well as the implications of this aggressive transformation are highlighted here.