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usually accompanied by enlargement of those organs, although hepatic dysfunction may also be present Bone marrow involvement is rare, but usually presents with cytopenias, which should prompt a bone marrow aspirate and biopsy Diabetes insipidus (DI) due to involvement of the posterior pituitary is the most frequent endocrine abnormality in LCH; some patients may present with an apparent “idiopathic” presentation of DI before other lesions are identified A few patients may present with diarrhea or malabsorption as colitis related to LCH has been described HLH is a very rare but severe and life-threatening systemic disease with rapid progression from presentation to death without appropriate intervention Thus, consideration of this diagnosis in the ED can be critical to outcome For these reasons, it is essential for the emergency clinician to have some familiarity with this disorder Congenital HLH usually presents in infants and very young children Other forms of HLH develop secondary to Epstein–Barr virus (EBV) infection, malignancy, or severe rheumatologic disorders or without a specific trigger Regardless of etiology, HLH presents with fever, hepatosplenomegaly, adenopathy, and rash Clinical Assessment All patients with suspected histiocytic disorders need a thorough history and physical examination as well as a rapid assessment of severity of illness Patients with HLH may have significant systemic illness with organ dysfunction and vital sign instability and will often require management in a critical care setting At the other extreme, patients with suspected localized LCH may require little to no intervention in the ED but need only close oncologic follow-up Pulse oximetry should be checked to screen for hypoxia and a chest x-ray obtained if hypoxia is detected Laboratory evaluation should include CBC, liver function testing, electrolytes to screen for DI, and inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) In HLH, laboratory analysis may reveal a markedly high serum ferritin as well as transaminitis, hypertriglyceridemia, hypofibrinogenemia, and cytopenias Bone marrow evaluation may show characteristic hemophagocytosis Oncologic consultation can guide the evaluation and management of systemically ill patients, as in the case of HLH, or allow for careful follow-up of more stable patients with suspected LCH TUMORS OF THE CENTRAL NERVOUS SYSTEM Goals of Treatment