Excerpt from Urticaria, Dermographism

Synonyms, Key Words, and Related Terms: dermatographism, urticaria, urticarial dermographism, factitious urticaria, allergy, allergic reaction, anaphylaxis, anaphylactoid reaction, angioedema, triple response of Lewis, linear wheal, whealing, red dermatographism, red urticaria, skin scratch reactions, hives, itching

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Background: Dermographism is a normal physiological response of the skin. The term literally means writing on the skin. Firm stroking of the skin produces an initial red line (capillary dilatation), followed by an axon-reflex flare with broadening erythema (arteriolar dilatation) and the formation of a linear wheal (transudation of fluid/edema) termed the triple response of Lewis. An exaggerated response accompanied by itching to this constitutional whealing tendency is seen in approximately 2-5% of the population and is termed symptomatic dermographism. Dermographism is the most common form of physical urticaria.

Pathophysiology: The exact mechanism of dermographism remains uncertain. Trauma may release an antigen that interacts with the membrane-bound immunoglobulin E of mast cells, which release inflammatory mediators, particularly histamine, into the tissues. This causes small blood vessels to leak, allowing fluid to accumulate in the skin. Other mediators possibly involved are leukotrienes, heparin, bradykinin, kallikrein, and peptides such as substance P.

Frequency:

Internationally: Symptomatic dermographism is the most common of the physical urticarias, affects approximately 2-5% of the population, and can occur with other forms of urticaria. Increased incidence has been reported in pregnancy (especially in second half), at the onset of menopause, in atopic children, and in patients with Behçet disease.

Mortality/Morbidity: Simple dermographism is the most common variant, and patients with this form are asymptomatic. However, other forms are associated with pruritus. Most people with dermographism are otherwise healthy. An association with thyroid disease has been described in some patients but remains controversial.

Race: No racial variance in prevalence is known.

Sex: Whether a sexual variance in prevalence occurs is unclear. None has been consistently reported, although one study on dermographism in children reported a female predominance (Martorell, 2000).

Age: Dermographism can appear in persons of any age but is more common in young adults. Peak incidence is in the second and third decades.