Unusual presentation of Rosai-Dorfman disease (RDD) in the bone in adolescents.

Rosai-Dorfman disease (RDD), or sinus histiocytosis with massive lymphadenopathy (SHML), is a rare idiopathic histiocytic disorder. The usual presentation of RDD is painless bilateral cervical lymphadenopathy. Extranodal RDD with lymphadenopathy occurs in almost 50% of patients but extranodal RDD, without lymphadenopathy, is very rare. Isolated RDD in the bone occurs in only 2% of patients but it is histologically similar to its nodal counterpart. There are only 14 previously reported cases of RDD in the bone without lymph node involvement in children. Here we describe two new patients--one with rib and lung involvement and the other with multi-osseous involvement.