Dermographism or dermatographism is an exaggerated wealing tendency when the skin is stroked. It is the commonest form of physical urticaria.
In 25-50% of normal people firm stroking of the skin produces first a white line, then a red line, then slight swelling down the line of the stroke, and a mild red flare in the surrounding skin. In 5% of the population this response is exaggerated enough to be called dermographism. In only a minority of these does it cause any symptoms.
1. Cause of dermographism
The exact cause of dermographic urticaria is unknown. Histamine is the main chemical released by mast cells when the skin is stroked, but other chemical mediators may also be involved.
Some patients with severe dermographism may have an antibody in their serum.
Occasionally dermographism is triggered by an allergy to some external agent such as penicillin, scabies or a worm infestation.
2. Clinical features
Dermographism can appear at any age but is most common in young adults. The onset is usually gradual, but in some the condition develops over a few days.
People with dermographism are usually otherwise healthy. Occasionally patients may have thyroid disease.
Many authors have noted there is an important nervous factor. Attacks of itching and subsequent weals from scratching occur at intervals and may be related to agitation and worrying situations.
Symptoms are often worse in hot conditions, for example, after a warm bath.
Minor pressure from clothing, chair seats, working with various tools, clapping the hands or energetic kissing, etc., may start up the weals.
They may develop after exercise if it is accompanied by knocks or pressure on the skin such as in rugby, wrestling or boxing.
Towelling after bathing may start weal production.
Once a few weals develop, subsequent scratching readily starts others in the vicinity. The weals are usually on the surface but some deep extension may occur and giant weals develop. However, these swellings die away rapidly and usually clear after half to one hour.
Dermographism can occur with other types of urticaria (hives) including those due to cold or pressure.
Dermographism may last for months or go on indefinitely. In many patients, however, it clears within a year or two, or at least the wealing is reduced to a degree which no longer causes significant symptoms.
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