What is dermographism?
Dermographism is an exaggerated wealing tendency when the skin is stroked. It is the commonest form of physical urticaria. It is also called dermatographism, dermatographia and dermatographic 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.
What is the 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 carry an autoantibody to some unknown cutaneous protein.
Who gets dermographism?
Dermographism can appear at any age but is most common in young adults.
- Dermographism can occur with other types of urticaria (hives) including those due to cold or pressure.
- An association with thyroid disease has been noted, but is likely a reflection of an underlying tendency to autoimmune disease and does not appear to have a causative relationship.
People with dermographism are usually otherwise healthy.
Clinical features of dermographism
The onset of dermographism is usually gradual, but in some the condition develops over a few days. Aggravating factors may include:
- Hot conditions, for example, a warm bath, shower or bed
- Towelling after bathing
- After exercise, especially if it is accompanied by knocks, such as occur in rugby, wrestling or boxing
- Minor pressure from clothing, chair seats, working with tools, clapping the hands, and other minor forms of pressure on the skin
- Nervousness, agitation and worrying situations.
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.
- The weals die away rapidly and usually clear after half to one hour.
Treatment of dermographism
General measures include avoiding the stimuli that set off bouts of itch, where possible. For example:
- Choose comfortable, loose clothing
- Avoid exposure to very hot water
- Pat dry gently after bathing
- If suspicious of a drug cause, consider stopping it if safe to do so.
Antihistamines usually give good relief from symptoms. Non-sedating options include:
Antihistamines may need to be continued daily for at least several months; intermittent therapy is of less value.
Resistant cases may find phototherapy helpful.
What is the outcome of dermographism?
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.