Chapter 29-19: Urticaria

TEXTBOOK PRESENTATION

Urticaria typically presents as an itchy rash with large or small, palpable, red areas over the entire body. The rash is transient, with no 1 lesion lasting very long. Both the rash and the pruritus respond to antihistamines.

DISEASE HIGHLIGHTS

1. Description of the lesion: transient pink to red gently elevated edematous papules and plaques that may coalesce into giant lesions. The lesions often leave purple discoloration or central clearing when they fade (Figure 29-14).

2. Characteristics of the lesion

   1. Individual lesions should resolve within 24 hours while new lesions may continue to develop.

   2. The eruption is typically accompanied by itch, but excoriations are rare.

3. Mucous membranes, eyelids, hands, and feet may develop deeper subcutaneous swelling manifesting as angioedema.

4. Most urticaria is acute, lasting < 6 weeks.

5. Urticaria is a hypersensitivity reaction to numerous insults.

   1. Etiologic factors can be remembered with the mnemonic I-I-I-I-I.

      1. Infection

      2. Infestation

      3. Ingestion (food or drug)

      4. Inhalation

      5. Injection

   2. Idiopathic should be added to this list.

6. Chronic urticaria (lasting > 6 weeks) can also be idiopathic, or associated with systemic disorders such as collagen vascular disease, malignancy, parasitosis, and chronic infection.

EVIDENCE-BASED DIAGNOSIS

1. Clinical findings of typical transient urticaria are diagnostic, and a skin biopsy is rarely indicated.

2. The morphologic differential diagnosis often includes the following:

   1. Erythema multiforme (because of the targetoid appearance of some urticaria)

   2. Insect bite reactions

   3. The early phases of bullous pemphigoid

3. Urticaria can be distinguished from all of the above disorders because it is the only one with lesions that last < 24 hours.

4. A careful history, including review of medications, recent exposures, and food ingestion, is the most important aspect of the evaluation to determine a cause.

5. Laboratory evaluation is sometimes undertaken in cases of chronic urticaria, but studies have shown that relevant results are so rarely found without other symptoms that this approach is discouraged.

TREATMENT

1. Identification of the inciting agent (medication, supplement, infection) is paramount and should be addressed as the first step in management.

2. Antihistamines are the mainstay of therapy. H₁-blockers should be given on a regular dosing schedule until the eruption is suppressed and then tapered gradually to prevent rebound flare.

3. Combinations of different H₁-blockers can be effective when a single agent is inadequate.

4. Addition of H₂-blockers may be helpful in refractory cases.