Excerpt from Urticaria, Pressure

Synonyms, Key Words, and Related Terms: vibratory urticaria, delayed pressure urticaria, dermatographism, PU, physical urticaria

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Background: Pressure urticaria (PU) is an uncommon form of physical urticaria. It may occur immediately, within minutes, after a pressure stimulus. More commonly, wheals develop after a delay of 4-6 hours after a pressure stimulus. The lesions may last for 8-72 hours. The hands, the feet, the trunk, the buttocks, the legs, and the face are the most common areas affected. Lesions can be induced by a variety of stimuli, including standing, walking, wearing tight clothes, or sitting on a hard surface.

Pathophysiology: The pathogenesis of PU is unknown. No allergen can usually be found. Mast cells are believed to play a role because injection of a compound "48/80", which causes depletion of mast cell mediators, prevents the induction of lesions in the injected area. Histamine levels are increased in lesional skin, and intracellular histamine levels are decreased in peripheral white blood cells. Despite these findings and the finding of increased stimulated histamine release, histamine is not likely to be the sole mediator in PU, given the relative unresponsiveness of conditions to antihistamine treatment.

Other possible mediators include eosinophils, given the elevated numbers of eosinophils, eosinophil cationic protein (ECP), and interleukin 5 found on the biopsies of some patients with PU, particularly bullous PU. Interleukin 6 has also been found in elevated concentrations in lesional skin.

Frequency:

In the US: PU is considered a rare entity, but some investigators have suggested that PU may be more common but not consistently recognized.

Mortality/Morbidity: PU is a chronic disease, with a mean duration of 9 years (range, 1-40 y). Depending on the severity of the disease and the associated symptoms, PU can be disabling, especially in patients who perform manual labor.

Sex: PU is slightly more common in men than in women.

Age: The peak age of onset is in the 20s and 30s (range, 5-63 y).