Dermatology · Allergic and Immunologic Skin Disorders
The facts most likely to be tested
Urticaria is characterized by transient, pruritic, erythematous wheals that typically resolve within 24 hours.
The primary pathophysiologic mechanism involves mast cell degranulation and histamine release in the superficial dermis.
Chronic spontaneous urticaria is defined by the presence of symptoms for greater than 6 weeks without an identifiable external trigger.
First-line treatment for symptomatic urticaria is second-generation H1-antihistamines such as cetirizine, loratadine, or fexofenadine.
Dermatographism is the most common form of physical urticaria, characterized by the development of wheals following mechanical stroking of the skin.
Angioedema involves deeper dermal and subcutaneous tissue swelling and must be evaluated for airway compromise if involving the lips, tongue, or pharynx.
ACE inhibitor-induced angioedema is a bradykinin-mediated process that does not typically present with concurrent urticaria or pruritus.
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A 28-year-old female presents to the urgent care clinic complaining of recurrent, intensely itchy skin lesions that have persisted for the past 8 weeks. She reports that individual lesions appear suddenly, last for several hours, and then disappear completely without leaving residual bruising or hyperpigmentation. She denies any recent changes in soaps, detergents, or medications, and she has no history of fever, joint pain, or respiratory distress. Physical examination reveals multiple erythematous, raised, blanching wheals of varying sizes scattered across her trunk and extremities. There is no evidence of mucosal swelling or respiratory compromise.
What is the most appropriate initial management for this patient?
Second-generation H1-antihistamine (e.g., cetirizine)
The patient's presentation of transient, pruritic wheals lasting longer than 6 weeks is diagnostic of chronic spontaneous urticaria, for which second-generation H1-antihistamines are the first-line therapy.
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Etiology / Epidemiology
Commonly triggered by IgE-mediated hypersensitivity to foods, medications, or infections. Atopy is a major risk factor.
Clinical Manifestations
Transient, pruritic wheals with dermatographism. Lesions typically resolve within 24 hours.
Diagnosis
Primarily a clinical diagnosis. Skin biopsy is reserved for lesions lasting >24 hours.
Treatment
First-line is second-generation H1 antihistamines. Avoid systemic corticosteroids for chronic cases.
Prognosis
Acute cases resolve in days; chronic urticaria lasts >6 weeks and often requires long-term management.
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Epidemiology & Etiology
Urticaria affects up to 20% of the population at some point in their lives. Common triggers include NSAIDs, antibiotics, food allergens, and viral infections. Chronic spontaneous urticaria is more common in adult females.
Pertinent Anatomy
The pathology is localized to the superficial dermis. Involvement of the deeper dermis and subcutaneous tissue defines angioedema.
Pathophysiology
Mast cell degranulation releases histamine, bradykinin, and leukotrienes. This increases capillary permeability, leading to localized fluid extravasation. The process is typically IgE-mediated, though non-immunologic pathways exist.
Clinical Manifestations
Patients present with circumscribed, raised, erythematous wheals that are intensely pruritic. Individual lesions are transient and blanch with pressure, often exhibiting dermatographism. Red flags include associated laryngeal edema, wheezing, or hypotension, which indicate anaphylaxis.
Diagnosis
Diagnosis is clinical based on history and physical exam. If lesions persist >24 hours, biopsy is required to rule out urticarial vasculitis. Laboratory testing is generally low-yield unless the history suggests specific systemic disease.
Treatment
Initiate therapy with second-generation H1 antihistamines (e.g., cetirizine, loratadine). If refractory, increase dose up to 4x standard dose or add H2 blockers. Avoid systemic corticosteroids for chronic management due to long-term toxicity. Use epinephrine for acute airway compromise.
Prognosis
Acute urticaria is self-limiting. Chronic urticaria persists for >6 weeks and significantly impacts quality of life. Monitor for anaphylaxis in patients with known triggers.
Differential Diagnosis
Angioedema: deeper tissue swelling without pruritus
Urticarial vasculitis: lesions persist >24 hours and are painful
Contact dermatitis: localized, delayed, eczematous reaction
Erythema multiforme: targetoid lesions, often post-herpetic
Bullous pemphigoid: tense bullae, subepidermal cleavage