Chapter 7. Dermatology

Clinical Features

Urticaria, or hives, are pruritic raised erythematous superficial skin wheals that arise in response to histamine, leukotrienes, prostaglandins, and other substances released by stimulated mast cells. Lesions develop and resolve quickly; individual lesions should resolve in < 24 hours. Urticaria is often associated with hypersensitivity reactions, including anaphylaxis. Symptoms are characterized as acute if they occur daily for < 6 weeks, and chronic if they occur for longer. Triggers can include allergic reactions to drugs, foods, insect stings, and rarely aeroallergens. Urticaria can also be caused by physical stimuli including cold, heat or exercise (cholinergic), pressure, vibration, and sun exposure. Infections including hepatitis, EBV, helminthes, and fungi have been associated with urticaria. Patients with collagen vascular diseases often develop urticaria. Differential diagnosis includes mastocytosis/urticaria pigmentosa, erythema multiforme, bullous skin disorders, or dermatitis herpetiformis. Obtaining a detailed history can help find an etiology. Urticaria that has been occurring for < 6 weeks usually does not require any laboratory workup. Laboratory tests may be done as indicated for chronic urticaria. Helminth infections would be associated with very high eosinophilia.

Emergency Department Treatment and Disposition

Attempt to identify the trigger based on a thorough history. Advise patients to discontinue or avoid the offending agent, if known. The main form of treatment includes H1 blockers (eg, diphenhydramine) given intravenously (IV) or orally. Second-generation antihistamines (eg, cetirizine) can be used once or twice a day until symptoms resolve. H2 blockers (eg, cimetidine, ranitidine) may be combined with H1 blockers. For patients with severe urticaria, interventions may include epinephrine given subcutaneously, corticosteroids given IV as hydrocortisone or methylprednisolone, or oral prednisone given first bolus followed by once-daily dose. Suspected anaphylaxis should be treated accordingly. Patients should be educated and sent home with injectable epinephrine. Urticaria can be very frustrating for the patient, and referral to an allergist can often help with management and investigation for the trigger.

Pearls

1. Urticaria is characterized by erythematosus, edematous lesions that are pruritic and evanescent.

2. If the lesions last longer than 24 hours, leave a mark, or are painful rather than pruritic, refer the patient for skin biopsy to rule out urticarial vasculitis.

3. The underlying cause for chronic urticaria is rarely found.

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