Q1. What Is Dermographism and How Does it Differ from Triple Response of Lewis?
Ans - The weal and flare reaction described by Lewis in response to stroking the skin, consists of development of an initial red line (capillary dilatation) followed by an axon reflex flare with broadening erythema (arteriolar dilatation) and formation of linear weal (transudation of edema fluid). Dermographism is also called skin writing, factitious urticaria or dermograhic urticaria. Dermographism is essentially an exaggeration of this triple response [Figure 1]. Dermographism or 'simple' dermographism, is noted in about 1.5%-5% of healthy individuals and is regarded as a normal physiological phenomenon. It has been postulated that it usually develops within five minutes of stroking the skin and persists for 15-30 min in contrast to the normal triple response of Lewis that subsides in less than 5-10 min. Symptomatic dermographism can be differentiated from simple dermographism by the presence of itching and a generally lower urticariogenic threshold.
Q2 - What Is White Dermographism?
Ans - On stroking the skin of atopic individuals, the rubbed area becomes erythematous, but the erythema is replaced in 10-15 seconds by pallor, which may persist for 60 seconds or more [Figure 2]. This phenomenon is called 'white dermographism' and is considered an abnormal vascular response in patients with atopic dermatitis.
Q3 - What Is the Method of Elicitation of Dermatographism?
Ans - Method of elicitation –Conventionally, for eliciting symptomatic dermographism, smooth blunt object (closed ball pen or a wooden spatula) is held perpendicular to the skin and used to apply a light stroking pressure on the volar forearm or upper back (skin should be unbroken and free from signs of infection and inflammation). Development of a pruritic palpable weal within 10 minutes in response to a light stroking stimulus is considered a positive response for development of symptomatic dermographism. A weal response without itch indicates simple dermographism. However the intensity of stroke produced by ballpoint pen can be highly variable. Hence a calibrated instrument that can be used for applying uniform pressure over the skin has been developed. The instrument friction test dermatographometer (FricTest®; Charité Hospital, Berlin, Germany) consists of a disinfectable plastic comb with four tips (which are 3.0, 3.5, 4.0, and 4.5 mm in length, respectively and 3mm width), which applies graded shearing forces to the skin. [Figure 3] This instrument is currently not available in India. An instrument called as Skin writometer is made available in India which although, not validated, can be used as an alternative to the above mentioned FricTest [Figure 4]. A closed ballpoint pen with an empty refill can also be used as a simple bedside alternative to the dermatogrophometer to elicit symptomatic dermographism.
Q4- What Is the Pathogenesis of White Dermographism?
Ans–The precise reason for white dermographism remains to be established.
The small blood vessels in atopic eczema show a tendency to vasoconstriction. This is substantiated clinically by the presence of white dermatographism, lower finger temperature, and pronounced vasoconstriction in response to cold. The same has been demonstrated through in vivo studies as a delayed blanch response to Acetyl choline, white reaction to nicotinic acid esters and abnormal reactions to histamine in affected skin.
There was an initial debate as to the cause of white dermographism – whether it was due to inflammation and oedema in the skin or vasoconstriction but studies with laser Doppler flow measurements have confirmed the latter.
Q5 – What Is the Significance of White Dermographism in Atopic Dermatitis?
Ans - White dermographism is considered as constitutional stigmata of atopic dermatitis. Although it is one of the minor diagnostic criteria according to Hanifin and Rajka, most of the studies have failed to find any statistical significance between its prevalence and atopic dermatitis. This finding is in corroboration with the study conducted in Indian population by Dhar S, et al.
It is often the first sign to appear in the initial stages of atopic dermatitis, and it is the last to disappear when the skin is returning to normal. Although it is known to appear more commonly in atopic dermatitis, it is not specific and is also seen to occur in infiltrative chronic inflammatory conditions, such as, disseminated neurodermatitis, psoriatic erythroderma, mycosis fungoides of the infiltrative type, and lymphoma associated erythroderma.
Q6 – What Are the Factors Influencing Elicitation of White Dermographism?
Ans - Elicitation of white dermographism depends on a number of factors.
1. Duration of atopic eczema
Experimental studies indicate that persistence of mild persistent dermatitis for a certain period of time is essential for the development of white dermographism and presence of severely acute dermatitic changes inhibits the development of white dermographism. This is the possible reason attributable to the high negative results of white dermographism in early infancy in patients with infantile eczema. In addition, it is speculated that the vascular reactivity of skin in early infancy is not mature enough to demonstrate white dermographism since at the time of birth the capillary beds are still disorganised as compared with the final adult pattern and it takes about 14-17 weeks in the post natal period to attain stability. Hence demonstrability of this skin reaction may not have any significant prognostic implications or any diagnostic significance in atopic dermatitis in early infancy and may only reflect chronicity and moderate degree of underlying dermatitic changes.
2. Site of elicitation of white dermographism-
It has been said to occur more easily on lower than on upper half of the body and on arms, legs and neck rather than on abdomen and trunk. Because of reduced turgor and tension on the skin may be difficult to elicit the reaction on these areas. Its occurrence may also be restricted to some localised skin sites.
3. Intensity of stroking
Even slight stroking can elicit white dermographism. The reaction to a stimulus that is too strong may be a red line with a white halo instead.
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