Atypical Cellular Disorders

Abstract
Some immunologic diseases are characterized by profound loss or primary dysfunction of a given population of cells. The atypical cellular disorders discussed here all bear some similarities in that abnormal proliferations of lymphocytes and macrophages or dendritic cells result in lymphadenopathy, skin rashes, bone lesions and infiltrations of nearly any other organ system. What are the similarities and the differences between Langerhans cell histiocytosis (LCH), sinus histiocytosis with massive lymphadenopathy (SHML) or Rosai-Dorfman disease, and Castleman’s disease (CD)? Studies on LCH have some advantages since it was described before the others, and organized clinical trials have been done since the 1980s. The understanding of SHML benefited from a registry maintained by Drs. Rosai and Dorfman. CD was described fifty years ago and for one subtype has the most clearly defined etiology (HHV-8 infection) of the three atypical cellular disorders discussed here.