Symptomatic dermographism, often also called urticaria factitia, belongs to the group of physically inducible urticaria and represents the most common sub-form of physical urticaria. It often occurs with other forms of urticaria. The triggering stimulus for itching and/or burning skin and the stripe-like wheals is the impact of shear forces on the skin, which arise, for instance when rubbing, scratching or chafing (Ill. 10, 11).
The frequency of symptomatic dermographism in the general population, depending on the source of literature, amounts to up 5 %. Particularly young adults between the ages of 20 and 30 are affected. The data on the duration fluctuate between 2 and 5 years, whereby these figures are of purely statistical nature and not applicable to individual patients.
As with other forms of urticaria the main symptoms of symptomatic dermographism are temporary wheals, flaring, itchiness and/or burning skin. Less commonly prickling, stinging and heat sensitivity are described. It is important that: the skin manifestations never occur spontaneously but exclusively at such spots at which shearing forces were applied, this means, for instance, areas where tight clothing rubbed against the skin or which were scratched. The strength of the shearing forces required as trigger varies considerably. Some patients report that the symptoms occur after taking a shower. In such cases the shearing force of the water jet or of following drying sufficed to trigger the symptoms. In other cases strong scratching triggers changes of the skin.
The wheals occur within seconds to but a few minutes on patients with symptomatic dermographism and can last up to several hours. The sequence often observed of the skin reaction is, as summarised briefly: After rubbing or scratching the skin it reddens (through increased blood flow) which is followed by the formation of a reddened aureole extending far beyond the trigger spot at which a wheal develops and itching begins. The wheal is initially still red. It then turns whitish and after a few minutes its full clinical picture appears. The symptoms then disappear in the same order as they appeared: The flare fades after a short time and then itchiness subsides and disappears together with the wheal. The wheals are stripe-like or elongated and their shape corresponds to the preceding stimulant on the skin.
As a rule no cause can be found for symptomatic dermographism. A medical examination, contrary to the cause of spontaneous chronic urticaria, for the underlying causes is therefore not indicated.
Diagnosing dermographic urticaria is relatively simple: most patients are aware that scratching is the trigger for wheals to develop. In the medical examination a wooden spatula or a special instrument with a so-called dermographometer, is stroked across the skin (for instance on the back or forearm) asserting moderate pressure. Almost all people will demonstrate skin reaction, the so-called dermographism (Greek for “writing on the skin”). In the case of healthy people a “red dermographism” which is no more than a short reddening of the skin as reaction to the mechanical stimulation. In patients with symptomatic dermographism, however, wheals develop with the typical itching flare which only disappears latest after several hours without further consequences.
How can the severity of the disease and the effectiveness of the treatment be determined? A dermographometer is used e.g. FricTest® (www.moxie-gmbh.de); this instrument consists of a flat plastic comb with 4 plastic pins of different lengths which are applied vertically to the skin and stroked over the skin under pressure (Ill. 11b). After 10 minutes every single pin is read. The so-called threshold value can be determined, i.e. the slightest shearing force required to trigger a wheal.
Because so little is known about the causes of dermographism, a causal treatment is not possible. All patients are first and foremost advised to avoid the triggering stimuli in as far as possible. This particularly included avoidance of all tight, pinching and scouring clothing and tight belts, to turn T-shirts “inside out” or to use laundry softeners for towels for instance. Ensure sufficiently rehydrating skin care is used to avoid additional itching from dry skin. What steps should be taken in addition? An attempt is made to completely prevent the occurrence with various drugs, indeed until symptomatic dermographism heals on its own. The most recommended drugs are simple dosing of non-sedating antihistamines (also called “antihistamines of the 2nd generation, for instance Loratadin, Cetirizin …). If symptoms continue to occur the dose can be increased up to the fourfold of the simple daily dose. If this does not lead to sufficient protection either, other drugs, e.g. Omalizumab may be of help. You get the best help from a dermatologist or an allergist.