EVIDENCE FOR A POLYCLONAL NATURE OF THE CELL INFILTRATE IN SINUS HISTIOCYTOSIS WITH MASSIVE LYMPHADENOPATHY (ROSAI-DORFMAN DISEASE)

Sinus histiocytic with massive lymphadenopathy (SHML), or Rosai-Dorfman disease, is rare histiocytic disorder of known origin which shares several cell markers with Langerhans' cell histiocytosis (LCK). Although Rosai-Dorfman cells exhibit an aberrant immunophenotype, the indolent clinical course of SHML suggests a reactive disorder rather than a neoplastic process. Until recently this was prevailing opinion concerning LCH also, but recent studies have detected clonal histiocytes in all forms of this latter condition, which is therefore considered a clonal neoplastic disorder with highly variable biological behaviour. To determine whether the histiocytic proliferation in SHML is polyclonal or clonal we used X-linked polymorphic loci to assess clonality in lesional tissues in two women. Polymorpic regions of the human androgen receptor (HUMARA) locus were amplified by polymerase chain reaction (PCR) analysis. The HUMARA locus was informative in both cases and, following digestion with methylation-sensitive enzymes, typical polyclonal X-inactivation patterns were observed. Since abnormal cells accounted for >90% lesional tissue cells, we conclude that Rosai-Dorfman histiocytic proliferation was polyclonal in the women studied.