DERMOGRAPHISM

 

Dermographism is the most common form of physical urticaria and is the one most likely to be confused with chronic urticaria. A lesion appears as a linear wheal with a flare at a site at which the skin is briskly stroked with a firm object . A transient wheal appears rapidly and usually fades within 30 minutes; however, the patient's normal skin is typically pruritic, so that an itch-scratch sequence may appear. The prevalence of

dermographism in the general population was reported as 1.5 percent and 4.2 percent, respectively, in two studies, and its prevalence in patients with chronic urticaria is 22 percent. It is not associated with atopy. The peak prevalence occurs in the second and third decades. In one study, the duration of dermographism was found to be longer than 5 years in 22 percent of individuals and longer than 10 years in 10 percent.

Elevations in blood histamine levels have been documented in some patients after experimental scratching, and increased levels of histamine, tryptase, SP, and VIP, but not calcitonin gene-related peptide, have been detected in experimental suction-blister aspirates. The dermographic response has been passively transferred to the skin of normal subjects with serum or IgE.

In delayed dermographism lesions develop 3 to 6 hours after stimulation, either with or without an immediate reaction, and last 24 to 48 hours. The eruption is composed of linear red indurated wheals. This condition may be associated with delayed pressure urticaria, and these two may, in fact, represent the same entity. Cold-dependent dermographism is a condition characterized by marked augmentation of the dermatographic response when the skin is chilled.