Health

Urticaria (hives) : Causes, Symptoms & Treatment

By Dr Daya

Posted on December 26, 2016

Urticaria

Urticaria (hives) is an outbreak of swollen, pale red bumps or plaques (wheals) on the skin.
Urticaria (hives) is a common disorder mediated by localized mast cell degranulation, which leads to dermal microvascular hyperpermeability. The resulting erythematous, edematous, and pruritic plaques are termed wheals.

In most cases, urticaria stems from an immediate (type 1) hypersensitivity reaction, in which antigens trigger mast cell degranulation by binding to immunoglobulin E (IgE) antibodies displayed on the mast cell surface. The responsible antigens include pollens, foods, drugs, and insect venom.
IgE-independent urticaria may result from exposure to substances that directly incite mast cell degranulation, such as opiates and certain antibiotics.
In the vast majority of cases, no clinical cause is discovered despite extensive searching.
Hereditary angioedema is caused by an inherited deficiency of C1 esterase inhibitor, which results in uncontrolled activation of complement.
The ensuing urticaria affects the lips, throat, eyelids, genitals, and distal extremities.
When the larynx is affected, the condition can be dangerous, since airway patency may be compromised.

The histologic features of hives often are subtle. There is usually a sparse superficial perivenular infiltrate of mononuclear cells, rare neutrophils, and sometimes eosinophils.
Superficial dermal edema creates more widely spaced collagen bundles.
Degranulation of mast cells, which normally reside around superficial dermal venules, is difficult to appreciate
with routine hematoxylin-eosin (H&E) stains but can be highlighted using a Giemsa stain.

Urticaria typically affects persons between 20 and 40 years of age, but no age is immune.
Individual lesions usually develop and fade within hours, but episodes can persist for days or even months. Persistent lesions sometimes are due to urticarial vasculitis, which is often associated with deposition of complement in dermal venules. Lesions range in size and nature from small, pruritic papules to large, edematous, erythematous plaques.
Increased vascular permeability leads to localized dermal edema.
Lesions can be confined to a particular part of the body or generalized. In a specific type of urticaria, termed pressure urticaria, lesions are found only in areas exposed to pressure (such as the feet or the buttocks). Although not life-threatening, hives can compromise quality of life by causing severe pruritus and social embarrassment.