Urticaria: Reviewing the basics

December 1, 2005

National report — Categorizing urticaria and following up with effective treatment can prove to be very challenging to the clinician, according to Aniko Kobza Black, M.D., attending physician, St. John's Institute of Dermatology and St. Thomas Hospital, London.

National report - Categorizing urticaria and following up with effective treatment can prove to be very challenging to the clinician, according to Aniko Kobza Black, M.D., attending physician, St. John's Institute of Dermatology and St. Thomas Hospital, London.

Urticaria describes short-lived cutaneous swellings and angioedema, or short-lived deeper swellings in the subcutaneous and submucosal swellings. Most urticarias fluctuate unpredictably and are called "ordinary" urticarias. Some may be caused by allergy, pseudoallergy, autoimmunity or infection, but on investigation most will be idiopathic.

"Urticarias can markedly reduce the quality of life due to itching, unsightliness and unpredictable nature of the condition (which is) similar to that of eczema outpatients or to medical patients waiting for a coronary bypass operation," says Dr. Kobza Black. "In addition," he says, "the resolution of chronic urticaria in any one patient is unpredictable, and it may persist for many years, with up to 50 percent of patients with urticaria associated with angioedema having their symptoms 10 years later."

The pathogenesis of urticaria is dependent on cutaneous mast cell activation. The presence of thyroid autoimmunity in patients with ordinary "idiopathic" urticaria suggests that an autoimmune mechanism also may cause the wealing process. This activity is predominantly due to IgG autoantibodies (of the Ig1 and Ig3 subtype) directed against the a-chain of the high affinity IgE receptor (FceRI) in approximately 33 percent of cases. These antibodies are functional; therefore, an autoimmune mechanism is present in up to 40 percent of patients with ordinary chronic urticaria.

"There are no commercial ways of identifying these patients," Dr. Kobza Black tells Dermatology Times, "but the autologous serum skin test (ASST) can be used as a screening test. The autoimmune urticarias tend to be more severe, though there is overlap, and therefore may respond well to conventional therapy."

History, examination, diagnosis

As some patients present without weals, a comprehensive history is essential for diagnosis, classification and elucidation of causative factors of the urticarias and for instigation of appropriate diagnostic investigations. Investigations are naturally based on the history.

"The location, shapes and sizes of weals, often described in detail by the patient, is rarely useful in diagnosis except the linear weals of dermographism and, sometimes, the small multiple symmetrical weals of cholinergic urticaria," Dr. Kobza Black explains.

If an allergic cause, such as food, is suspected for acute urticaria this can be confirmed by a specific IgE blood test and, if the reaction is not too severe, by prick or intradermal tests. If a predominantly physical cause is suspected, usually when weals last less than one hour (except in delayed pressure urticaria), then confirmation can be made by appropriate physical challenge tests.

Dr. Kobza Black stresses that in his experience, "Performing an extensive panel of investigations in addition to a standardized questionnaire in a patient without any suggestive factor in the history added little to the final diagnosis and is to be discouraged. Patients frequently suspect food allergy, but this is rarely found in chronic urticaria."

In chronic ordinary urticaria, up to 40 percent of patients may have some element of associated delayed pressure urticaria. For ordinary chronic urticaria where there are no clues from the history, only a full blood count and ESR are suggested. In the event of eosinophilia, the presence of parasites can be sought. A high ESR warrants further investigation of a systemic cause - which is rare - or might suggest urticarial vasculitis.

Urticarial vasculitis is suspected when weals persist for 48 hours and are associated with systemic symptoms. It represents only 5 percent of urticarias, and a skin biopsy can confirm the diagnosis. Drugs such as colchicine, dapsone or hydroxychloroquine may be helpful, but sometimes, systemic oral steroids may be necessary.

Treatments

Dr. Kobza Black suggests low-sedation antihistamines as the treatment of choice. The dose can be increased above the recommended dose for some for their anti-allergic effect, but sedation may be enhanced. A potentially promising second-line treatment, usually in addition to an antihistamine, is the class of leukotriene receptor antagonists such as Montelukast 10 mg at night.