Sinus histiocytosis with massive lymphadenopathy. Occurrence in identical twins with retroperitoneal disease.

Sinus histiocytosis with massive lymphadenopathy (SHML) was originally defined as a relatively specific benign pseudolymphomatous disorder. Although the etiology remains unknown, the spectrum of SHML has been expanded to include predominance of extranodal disease in some patients, clinically significant immunologic abnormalities in 10% of patients, and fatal outcome in 7% of patients. We report the rare occurrence of SHML in identical twins; to our knowledge, SHML in identical twins has been reported only once previously. The two patients described are also unusual because of the predominance of retroperitoneal disease with minimal peripheral adenopathy. After a seven-year clinical course, one twin died of extensive retroperitoneal disease, liver failure, bleeding diathesis, and seizure disorder. The other twin is alive after a six-year course of progressive retroperitoneal disease.