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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

ETIOLOGIES

IgE-Mediated, Type I Reaction Direct Mast Cell Activation

Medications Narcotics

Stinging insects Muscle relaxants

Foods and food additives Vancomycin

Aeroallergens Radiocontrast

Contact allergens Tomatoes

Blood products Strawberries

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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