Pediatric emergency medicine trisk 1850 1850

causing degranulation of mast cells (e.g., radiocontrast material). Episodes of
urticaria lasting less than 6 weeks are termed transient or acute. The most
common causes of urticaria are infection, insect bites, drugs, and foods. Chronic
urticaria is defined as that which lasts for more than 6 weeks. No cause is found
in 90% of children. These cases include the physical urticarias or urticarial
vasculitis. The lesion itself follows vasodilation and leakage of fluid and red
blood cells from involved vessels. The vascular damage can be caused by
mediators such as histamine complement and immune complexes. IgE can attach
to and cause degranulation of mast cells in sensitized individuals, with resulting
histamine release.

Clinical Manifestations
The typical urticarial lesions are familiar to all physicians. They can be localized
or generalized (involving the entire body). At times, the lesions are giant with
serpiginous borders. Individual wheals rarely last more than 12 to 24 hours. Most
commonly, the lesions appear in one area for 20 minutes to 3 hours, disappear,
and then reappear in another location. The total duration of an episode is usually
24 to 48 hours; however, the course can last 3 to 6 weeks. In young children,
urticaria may have an annular or polycyclic (coalescent annular) or arcuate
(partially annular) appearance and may be associated with edema of the hands or
feet. Because this is frequently confused with EM (which manifest with more
fixed, targetoid lesions), this annular urticarial hypersensitivity has sometimes
been referred to as urticaria multiforme.

Management
Acute relief can be accomplished by oral diphenhydramine 1 mg/kg (max 50 mg).
Oral antihistamines are useful for maintenance therapy for transient urticaria. H1
antihistamines for 4 to 6 weeks are usually effective for controlling urticaria.
Many recommend combinations of H1 and H2 antihistamines, but there is
currently insufficient evidence to support this as a routine practice. Shorter-acting
agents like hydroxyzine can be used for breakthrough.

Suggested Readings and Key References
General
Eichenfield LF, Esterly NB, Frieden IJ. Textbook of Neonatal Dermatology.
Philadelphia, PA: Elsevier Health Sciences, 2014.
Goldsmith L, Papier A. VisualDx: Essential Pediatric Dermatology. Visual Dx:
The Modern Library of Visual Medicine. Philadelphia, PA: Lippincott Williams