Diagnostic Considerations
Systemic mastocytosis and urticaria pigmentosa are associated with a positive Darier sign.
Forms of false dermographism (superficially similar conditions that are not associated with urticaria) must be ruled out. These include the following:
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White dermographism – This is a blanching response resulting from capillary vasoconstriction after skin stroking and is more pronounced in persons with atopy
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Black dermographism – This is a black or greenish discoloration of the skin occurring after contact with certain metallic objects
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Yellow dermographism – This probably results from bile pigment deposits in the skin
Also consider latex allergy. Golberg et al presented a case series of 15 patients with symptomatic dermographism mimicking the symptoms of latex allergy, most commonly on the hands and genitalia. [12] Young atopic females and those in occupations involving regular use of gloves were more likely affected. Additionally, a flowchart has been devised to help guide clinicians in assessing patients with glove-related hand urticaria. [13]
Differential Diagnoses
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Dermographism or skin writing on forearm.
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Appearance of the word "Dermatographia" on a human arm 15 minutes after the letters have been traced with a blunt object on the skin. A type of urticaria or "hives", also known as dermatographic urticaria, dermatographism, or "skin writing".
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Dermographism urticaria. Courtesy of Professor Raimo Suhonen and DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/s/dermographism2.jpg).
