Urticaria

Description

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  Urticaria, or hives, is divided into acute and chronic forms based on the duration of the hives.

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  Acute urticaria, by definition, lasts for less than 6 weeks, whereas chronic urticaria lasts more than 6 weeks.

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  Urticaria is a common, pruritic, distinctive reaction pattern.

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  Transient, migratory, edematous, pink to red plaques vary in size and shape. Individual lesions typically last less than 24 hours.

History

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  The etiology or trigger of most cases of urticaria is undetermined.

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  Acute urticaria may occur at any age.

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  It is more common in atopic individuals and is notoriously intensely pruritic.

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  Hives are caused by histamine release induced by allergens or triggers, such as medications, injections, foods, or airborne allergens.

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  Angioedema is a histologically deeper variant of urticaria, is somewhat less pruritic, and more commonly affects mucosa.

Skin Findings

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  The edematous plaques are red or pink to flesh-colored and may be surrounded by a white or pink halo.

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  Individual lesions vary in size, from 2 mm papules to 3 cm or larger wheals.

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  They are typically round or oval in shape and can become polycyclic and confluent.

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  The plaques change size and shape and migrate and regress over time.

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  This is a dynamic process, and new lesions evolve as old ones resolve.

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  Rarely, bullae or purpuric lesions appear with intense swelling.

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  The distribution is usually generalized and haphazard.

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  Linear lesions suggest dermatographism, a type of hive created by scratching.

Laboratory and Testing

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  There are no reliable routine studies for diagnostic confirmation of urticaria.

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  Biopsy is usually not required for diagnosis of acute hives.

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  If urticarial vasculitis is suspected, a biopsy can help confirm this diagnosis.

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  For the most part, urticaria is a clinical diagnosis.

Differential Diagnosis

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  Medication allergy or eruption

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  Viral exanthem

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  Bite reaction (papular urticaria)

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  Bullous pemphigoid (early stages)

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  Urticarial vasculitis

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  Hereditary angioedema (mucosal involvement)

Treatment

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  All suspected triggers, such as medications, food, inhalants, and injections, should be discontinued.

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  Antihistamines are typically administered initially: sedating type 1 histamine receptor antagonists (e.g., hydroxyzine [10 mg, 25 mg, 50 mg, 100 mg] 10 mg/5 mL) can be helpful but are limited by drowsiness. They are administered every 4 or 6 hours.

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  The nonsedating antihistamines (e.g., cetirizine 5 mg, 10 mg) are also helpful but may have to be used in combination with sedating histamine-1 (H ₁ )-blocking antihistamines. They are taken once every 24 hours but may be taken twice a day in difficult cases.

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  Prednisone is rapidly effective and can be given periodically; it may work in patients whose condition is difficult to control with antihistamines.

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  Combinations of H ₁ and H ₂ blockers is another treatment strategy.

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  Doxepin, a tricyclic antidepressant and an antihistamine, can be used in recalcitrant cases.

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  Epinephrine is administered for extensive, severe cases, but the effects are short-lived.

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  Cool, soothing baths can be suggested.

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  Hot showers should be avoided because they worsen the pruritus afterward.

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  Topical steroids are generally not effective.

Pearls

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  The etiology may not be discovered in most cases.

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  By definition, acute urticaria resolves within 6 weeks, with or without treatment.

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  Individual hive or urticarial lesions migrate, change in shape, and typically resolve within 24 hours.

  
  
  

Description

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  Chronic urticaria is defined as urticaria or hives of the skin lasting more than 6 weeks.

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  This variation of hives requires investigation to the etiology of the urticaria, which can require significant workup.

History

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  Chronic urticaria is usually easily diagnosed but presents a treatment and management dilemma.

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  The underlying cause of chronic urticaria is discovered in only 5% to 25% of cases.

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  People of all ages are affected, but the highest incidence is in young adults.

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  The course of the disease is unpredictable, and the disease can last months or years.

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  Patients should be evaluated for the “five I's”:

  • Ingestants (most common): medications, foods, additives.

  • Inhalants: dust, feather, pollen.

  • Injectants: vaccines, drugs, stings, bites.

  • Infections: bacterial, viral, fungal, parasitic.

  • Internal diseases: chronic infections, thyroid disease, lupus erythematosus, occult cancer (rare).

Skin Findings

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  Clinically, chronic and acute urticarias are indistinguishable.

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  The edematous wheals and plaques are pink to red in color, figurate, and annular, with central clearing.

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  Lesions vary in size from just millimeters to areas that can cover an entire hand.

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  These plaques can be coalescing and polycyclic, change in size and shape over time, and migrate.

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  Individual lesions resolve within 24 hours, whereas new lesions continue to appear.

Laboratory and Testing

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  The cause may be unclear after routine history and physical examination.

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  Laboratory tests may be ordered but are rarely helpful.

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  Tests to consider include a complete blood count, sinus radiographs to evaluate for sinusitis, dental radiographs to evaluate for an occult dental abscess, rapid streptococcal test or pharyngeal culture, and a thyroid-stimulating hormone and thyroid microsomal antibody test for autoimmune thyroid disease.

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  Other tests may be acquired slowly based on the physical signs and symptoms of the patient.

Differential Diagnosis

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  Physical urticaria

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  Erythema multiforme

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  Urticarial vasculitis

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  Bullous pemphigoid (early stages)

Treatment

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  Antihistamines (H ₁ type) are prescribed initially, most commonly diphenhydramine and hydroxyzine.

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  They are the backbone of therapy for acute and chronic urticaria.

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  Hydroxyzine 10 to 25 mg or diphenhydramine 25 to 50 mg can be administered every 4 hours, up to 100 mg every 4 hours as needed, but can be sedating.

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  Nonsedating antihistamines (H ₁ type) should be considered for daytime use and include cetirizine, desloratadine, and fexofenadine.

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  H ₁ -blocking antihistamines may be combined with H ₂ -blocking antihistamines, such as cimetidine 400 mg twice daily or ranitidine 150 mg twice daily.

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  Doxepin, a tricyclic antidepressant and antihistamine, can be prescribed in difficult cases.

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  Oral steroids are a second line of treatment for hives; however, their use for chronic urticaria is controversial and sometimes detrimental, especially if high doses are required.

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  Epinephrine is rarely required; the effect is short-lived.

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  Empiric antibiotic therapy may be tried if an occult infection, such as a tooth abscess, or sinusitis is suspected.

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  Despite aggressive therapy, many cases of chronic urticaria persist indefinitely.