Rosai-Dorfman disease: Ultrasonography and histopathology study of a soft tissue mass in the forearm.

Rosai-Dorfman disease (RDD) is uncommon in daily practice, but needs to be ruled out in rheumatologic conditions to elucidate a wide differential diagnosis. Beside its typical presentation, soft tissue masses can be easily seen in our Rheumatology clinics. Ultrasonography widely extended in our specialty, could also play a role in the diagnosis, to end up with the histological confirmation of the disease.