Browse the corpus

General lnternal Medicine Urticaria Diagnosis The hallmark of urticaria (hives) is the wheal, a superficial, pruritic, erythematous, well-demarcated, intermittently present plaque. In acute urticaria, intermittent hives are present for 6 weeks or less. In chronic urticaria, intermittent hives are present for greater than 6 weeks. Individual lesions usually disappear within hours without residual skin discoloration. Food allergz (shellfish, peanuts, tree nuts), viral infection, and medication reaction are the most common causes of acute urti- caria. Infrequent but important causes of urticaria include autoimmune thyroid disease and malignancies, particularly lym- phoma. Urticaria can also develop with pressure, cold, heat, vibration, water, or sunlight. In most patients with chronic urticaria, a definite cause is not identified. Limited targeted laboratory testing is indicated when clinical suspicion suggests a cause, but routine, extensive testing should not be performed. DO]I'T BE TRICKED . Do not select ANA, patch testing, or specific IgE measurements for acute or chronic urticaria. o Painful lesions persisting >24 hours with purpura/ecch5rmoses on resolution are likely the result ofurticarial vasculitis. Definitive diagnosis is made by skin biopsy. 53iif::' l'*,i;:;"i.; Differential Diaqnosis of Udicaria lf you see this... Select this... 1 ESR, t CRB lesions persisting >24 hours; purpuric papules Vasculitic urticaria; perform skin biopsy Fever, adenopathy, arthralgias, and antigen or drug exposure Serum sickness; measure CRP, ESR, and complement levels Features of anaphylaxis, obvious allergen exposure lmmediate hypersensitivity reaction; treat emergently with epinephrine Marked eosinophilia Parasitic infection, possibly strongyloidiasis, filariasis, or trichinosis (especially with periorbital edema) Treatment Select nonsedating antihistamines as first{ine therapy. DO]I'T BETRISKED . Measurement of Cl inhibitor levels is not indicated in patients with urticaria, because C1 inhibitor deficiency, seen in hereditary angioedema, is not associated with hives.

53iif::' l'*,i;:;"i.; Differential Diaqnosis of Udicaria lf you see this... Select this... 1 ESR, t CRB lesions persisting >24 hours; purpuric papules Vasculitic urticaria; perform skin biopsy Fever, adenopathy, arthralgias, and antigen or drug exposure Serum sickness; measure CRP, ESR, and complement levels Features of anaphylaxis, obvious allergen exposure lmmediate hypersensitivity reaction; treat emergently with epinephrine Marked eosinophilia Parasitic infection, possibly strongyloidiasis, filariasis, or trichinosis (especially with periorbital edema) Treatment Select nonsedating antihistamines as first{ine therapy. DO]I'T BETRISKED . Measurement of Cl inhibitor levels is not indicated in patients with urticaria, because C1 inhibitor deficiency, seen in hereditary angioedema, is not associated with hives. TESTYOURSETF A 3l-year-old man has a 2-week history of hives. Individual lesions persist for less than 24 hours and are not worsened by cold, sunlight, or pressure. AIISWER: For diagnosis, choose acute urticaria. For laboratory evaluation, order no additional diagnostic studies. Fortreatment, select an H,-blocker such as cetirizine. Urtioria: Urticaria is characterized by small white, pink, or flesh-colored pruritic papules. 172