This is a spectrum of disease that encompasses Letterer-Siwe disease, Hand-Schüller-Christian disease, and eosinophilic granuloma. The disorder is characterized by the proliferation of Langerhans' histiocytes in the skin and other organ systems. Figure 21-7 shows the characteristic seborrheic-like, scaly, erythematous eruption on the scalp, face, and ears. Figure 21-8 shows a more popular presentation in a similar location. The presence of petechiae is a particularly helpful sign. Diagnosis is confirmed by skin biopsy and electron microscopy. More rapid confirmation is sometimes possible if one observes the presence of histiocytes in a lesion that has been scraped onto a microscopic slide and stained. Langerhans' cell histiocytosis may be accompanied by hepatosplenomegaly, lymphadenopathy, anemia, and thrombocytopenia.