Lymph node involvement by Langerhans cell histiocytosis: a clinicopathologic and immunohistochemical study of 20 cases.

Twenty cases of Langerhans cell histiocytosis (LCH) involving lymph nodes with no other sites of disease are presented. The patients were 12 men and 8 women between 3 months and 68 years of age. Seven patients were younger than 11 years; the other 13 patients were older than 16 years. Clinically, all patients presented with lymphadenopathy and underwent excisional biopsy; clinical and imaging studies did not reveal abnormalities in other organs. Cervical lymph nodes were most commonly involved; other lymph nodes involved included axillary, inguinal, and supraclavicular. Histologically, LCH in lymph nodes had 3 main architectural patterns: (1) preserved nodal architecture with subtle involvement, (2) subtotal effacement of nodal architecture, and (3) total effacement of nodal architecture. There was a gradient of involvement by LCH from focal sinus involvement to diffuse sinus involvement and from focal paracortical involvement to diffuse paracortical involvement. In some cases, focal involvement was initially unrecognized because of the subtle nature of the changes in the lymph node, posing difficulties for diagnosis. Langerhans cells in the involved areas showed strong positivity by immunohistochemical studies for S100 protein and CD1a in all 11 cases assessed. In conclusion, LCH can initially manifest clinically with involvement limited to lymph nodes. Recognition of the different patterns of LCH, particularly cases with subtle involvement, is important for recognizing this disease and separating LCH from other more common causes of lymphadenopathy.