Urticaria, described by the patient as itchy welts, can appear as 2 to 10mm raised papules surrounded by erythema that involve the superficial portion of the dermis. When the mediator release (primarily histamine) from mast cells occurs deeper in the dermis and subcutaneous tissue, the result is angioedema or swelling.

Acute Urticaria and Angioedema

Acute urticaria (and/or angioedema) is very common, occurring at some point during the lifetime of about a quarter of the population. In about a third of the cases, the cause is a food or drug, and the patient makes the obvious connection. One example would be the presentation of hives immediately after eating shrimp or beginning an antibiotic. In the remainder of the cases, no cause is ever found. The problem is usually self-limiting and lasts less than 4 weeks.

• Atarax or Benadryl are the standard symptomatic treatment for urticaria. Unfortunately, sedation often is a side effect with these medications.

• The non-sedating antihistamines Zytec 10 mg QD or Allegra 60 mg BID also work well, as does a short course of oral prednisone, 40 to 60 mg QD in more severe cases. Lab testing or specialty consultation is generally not necessary.

The sudden onset of edema of the lips, face, or tongue is typical of allergic angioedema associated with ACE inhibitors and other medications. Airway management is imperative. See the Anaphylaxis chapter for the management of this condition.

Chronic Urticaria and Angioedema

Chronic urticaria (and/or angioedema) refers to a duration of symptoms longer than 4-6 weeks. In contrast to the acute variety, it is only rarely caused by IgE mechanisms such as food or drug allergy. In fact, more than 90 percent of the cases turn out to be idiopathic, or of unknown cause. The prognosis for eventual spontaneous resolution is good, and most of the patients are healthy adults for whom the symptoms are nothing more than a nuisance.

However, rare cases are associated with underlying malignancy, liver disease, autoimmune disease such as lupus, and inapparent infection, so a careful history, review of systems, and physical exam is recommended. If there is no weight loss, fever, or malaise symptoms, an idiopathic urticaria will probably be the diagnosis, and the patient should probably be told that a cause is unlikely to be found. As screening tests, a complete blood count (CBC), differential, erythrocyte sedimentation rate (ESR), perhaps an antinuclear antibody (ANA), and total hemolytic complement are reasonable.

Cholinergic (heat-induced) and cold urticaria are physical urticarias sometimes confused with the chronic form. Cholinergic hives occur consistently with exercise or hot showers (often like heat rash or prickly heat). Cold urticaria is precipitated by swimming in cold water or by cold weather, and is usually apparent in the history. Treatment of chronic urticaria is the same as for the acute forms.