Langerhans cell histiocytosis (LCH) is a systemic disease associated with the proliferation and accumulation (usually in granulomas) of Langerhans cells in various tissues.

Chronic active Epstein-Barr virus (EBV) infection is an uncommon outcome of EBV infection and may present as a waxing and waning or fulminant syndrome. Unlike acute infectious mononucleosis, wherein EBV establishes lifelong infection and survives by maintaining a delicate balance with the host as a latent infection, in chronic active EBV infection the host-virus balance is disturbed.