In some patients, an increase in blood histamine levels is seen after experimental scratching. Usually, make the diagnosis by observing the clinical response after using moderate pressure to stroke or gently scratch the skin. The site is important, since areas protected from regular pressure and environmental influences, such as the back, are more reactive than buttocks and limbs. Biopsy specimens show dermal edema with a few perivascular mononuclear cells. Antihistamines almost always provide good relief from symptoms.
Nonsedative antihistamines are the drugs of choice.
In some patients, several antihistamines may need to be tried or a combination of two may need to be used simultaneously. Sedative antihistamines such as hydroxyzine occasionally may help. Regular treatment may need to be continued for several months. Occasionally, surprisingly small quantities may achieve relief. The symptomatic benefit of the addition of H2-receptor antagonists to treatment remains controversial, although studies have shown a further small reduction in whealing response.