OCTOBER 27, 2011 GOOD MORNING! WELCOME APPLICANTS!

Differential Diagnosis of Urticaria Viral exanthem Atopic dermatitis Contact dermatitis Toxic drug eruption Insect bites Bullous pemphigoid Erythema multiforme Plant induced reactions Cutaneous small vessel vasculitis Pityriasis rosea (early lesions) Mastocytosis

URTICARIA Urticaria – intensely pruritic, erythematous plaques that appear over the course of minutes, enlarge and coalesce with other lesions, then disappear within a few hours Acute = new onset; present less than 6 weeks Chronic = occurring most days of the week for >6 weeks; 1/3 of acute will become chronic Papular Physical (cholinergic, dermatographism) Angioedema – can accompany urticaria Swelling deeper in the skin

EPIDEMIOLOGY Affects 20% of people at some point in life 3% of preschool children 2% of older children Fever than 5% have documented IgE-mediated allergic urticaria 15% have physical urticaria Most fall into “idiopathic” group No specific cause is found in most cases

PATHOGENESIS Histamine is the primary mediator Released directly from cutaneous mast cells in response to certain foods or drugs Complement fragments (activated by immune complexes) may activate mast cells to release histamine or exert direct vasoactive effects on cutaneous blood vessels Papular urticaria – basophilic infiltrate; delayed hypersensitivity Physical urticarias – neuropeptide mediated

ETIOLOGIES *80% of cases due to infection in some pediatric series

ETIOLOGIES

IgE-Mediated, Type I ReactionDirect Mast Cell Activation MedicationsNarcotics Stinging insectsMuscle relaxants Foods and food additivesVancomycin AeroallergensRadiocontrast Contact allergensTomatoes Blood productsStrawberries Stinging nettle plant

CLINICAL MANIFESTATIONS Sudden in onset, pruritic, characterized by red raised 2- to 15-mm flat-topped wheals scattered over the body

CLINICAL MANIFESTATIONS Wheals commonly last from 20 minutes to 3 hours and then disappear, and reappear in other areas An entire episode of transient urticaria often lasts 24 to 48 hours Rarely as long as 3 weeks Labs are typically normal Consider CBC, UA, ESR, LFTs to detect underlying disorder in the 30% of pts. that will progress to chronic

ANGIOEDEMA Subcutaneous extension of lesions Large swellings that have indistinct borders around the eyelids and lips May also appear on the face, trunk, genitalia, and extremities Face, hands, and feet in 85% 50% of children with urticaria will have angioedema

PAPULAR URTICARIA Grouped on exposed areas Last for 10 to 14 days 10- to 20-mm wheal surrounding a 2- to 4- mm red papule Usually the result of an encounter with animal fleas or mites Difficult to convince parents of etiology when whole family exposed

MANAGEMENT 2/3 cases are self-limited and resolve spontaneously H1 antihistamines Second generation agents Minimally sedating, free of anticholinergic effects *First line therapy Cetirizine, Levocetirizine, Loratadine, Desloratadine, Fexofenadine First generation agents More sedating, anticholinergic side effects Helpful at bedtime Diphenhydramine, hydroxyzine

MANAGEMENT H2 antihistamines Combined with H1 may be more effective for acute urticaria Ranitidine, nizatidine, famotidine, cimetidine Glucocorticoids A brief course (a week or less) added to antihistamines may help gain control of symptoms Do not inhibit mast cell degranulation, but suppress a variety of inflammatory mechanisms Appears to be helpful, but may not be necessary

PROGNOSIS An extensive allergy evaluation is not indicated for children with acute urticaria An evaluation of chronic urticaria should be guided by history Papular urticaria Hypersensitivity to ectoparasites declines after 6 to 12 months, and the child may no longer be sensitive, even while still exposed Physical urticarias are more persistent Last 2 to 4 years, or into adulthood

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