Pediatric emergency medicine trisk 2674 2674

Timely recognition of histiocytic diseases can be lifesaving. The most common
histiocytic disease, Langerhans cell histiocytosis (LCH), rarely requires emergency
care, whereas hemophagocytic lymphohistiocytosis (HLH) is a life-threatening
illness that can be rapidly fatal without appropriate intervention.
CLINICAL PEARL AND PITFALLS
Consider HLH in the acutely ill infant or young child as these patients can
deteriorate quickly and require urgent oncologic consultation and critical
care support.

Current Evidence
Histiocytic diseases are a complex and sometimes confusing group of disorders for
two reasons. First, several different disease entities make up this group, although
efforts have been made to simplify the terminology. Second, significant clinical
heterogeneity exists between the major disease entities. Histiocyte is a term referring
to several different cells that are thought to derive from a common CD34+
progenitor in the bone marrow. Depending on the cytokines to which the progenitors
become exposed, the differentiation can yield tissue macrophages, dermal/interstitial
dendritic cells, or Langerhans cells. In general, histiocytic diseases are rare; of the
group, the most common is LCH, which has an incidence of three to five cases per
million children.

Clinical Considerations
Clinical Recognition
LCH has clinical heterogeneity and the locations involved have implications for
therapy and prognosis. Low-risk LCH may present at any age and systemic
symptoms are rare. Skin, bone, lymph nodes, or a combination of these are most
commonly involved. Skin involvement can present as a red papular rash, resembling
a candidal diaper rash, which may appear on the groin, abdomen, back, or chest.
There may also be seborrheic flaking of the scalp, often misdiagnosed as “cradle
cap” in infants, draining otitis externa, or ulcerative lesions behind the ears, on the
scalp, or in the genital region. Bony involvement may be asymptomatic or painful.

A lytic lesion of the skull causing a tender mass is the most common but any bone
may be involved. Loose teeth from involvement of the jaw may occur. Certain sites
of disease have become known as “risk” organs because their involvement implies
more aggressive disease. These patients are often very young with disease that
involves the lung, liver, spleen, and/or bone marrow. Lung involvement is rare but
worrisome and usually manifests first as hypoxia. Liver and spleen involvement is