Urticaria (hives)
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Introduction
Urticaria is a cutaneous and vascular reaction characterized by well-circumscribed areas of dermal edema and erythema. Angioedema, mediated by subcutaneous or submucosal swelling, often accompanies urticaria.
Fever, arthralgia, and bullae are rarer clinical manifestations.
30-40% of people will develop hives during their lifetime. It occurs most often between ages 20-40. Women are more affected than men.
Individual hives develop and fade within hours, but episodes can last for days or months.
Hives can range from small, pruritic nodules to large edematous plaques.
Areas exposed to pressure, such as the trunk, distal extremties, and ears, are most commonly affected.
Mast cell degranulation releases histamine, kinins, eicosanoids, neuropeptides, and other mediators of vasodilation.
The Case of...
a simple case introducing clincial presentation and calling for a differential diagnosis to get students thinking.
Causes and Risk Factors
In the majority of cases, no underlying cause may be found.
Other causes include:
- foods: nuts, shellfish, strawberries, eggs
- insect bites/stings
- infections: sinusitis, dental abscess
- viruses: hepatitis, mono
- bacteria (strep)
- fungi
- parasites
- spirochetes
- drugs: radiocontrast, NSAIDs, antibiotics
- physical stimuli: pressure, vibration, heat, cold, water
- systemic disease: thyroid, connective tissue disease, hepatitis, malignancy
Allergy testing is not clearly useful in investigation of urticaria.
Chronic urticaria is thought to be autoimmune.
Pathophysiology
Hives result from a final common pathway for a number of imunologic and non-immunologic triggers, leading to mast cell degranulation. These are most often IgE dependent, though degranulation can also happen due to direct chemical activation of mast cells.
Mast cell histamine release leads to cutaneous vasodilation and fluid extravasation, forming the characteristic wheals.
Angioedema is close lrelated to urticaria and is characterized by deeper edema involving both the dermis and subcutaneous fat.
Histologically, collagen bundles are more widely spaced and displaced by lymphatic and blood-filled spaces.
Signs and Symptoms
- history
- physical exam
History
Physical Exam
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
Diagnostic Imaging
Differential Diagnosis
Treatments
Avoid triggers
diphenhydramine (Benadryl) is a helpful first-line agent.
hydroxyzine is effective, including in infants. Use
antihistamines, one or more classes simultaneously
mast cell stabilizers (ie Zaditen)
corticosteroids
Consequences and Course
Resources and References
Topic Development
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