Black Dermographism: An Uncommon Cause of Skin Discoloration.

A 24-year-old newly married Indian housewife presented with recent onset of asymptomatic symmetrical blackish discoloration over medial sides of her third toes. She was looking distressed by progressive discoloration, which could not be completely wiped off with a wet cloth. On further enquiry, she stated that the alteration in the color of her toes appeared after she started wearing silver toe rings following her marriage. The silver rings constantly rubbed against the affected skin on the medial aspect of third toes. She had no similar pigmentation in the past, nor did she have hyperhidrosis. There was no history of intake of any systemic medications or application of topical medications. She was otherwise healthy.

On examination there was irregular black smudge measuring 2 cm × 1 cm over medial aspect of bilateral third toes [Figure 1]. Plantar hyperkeratosis was also seen in the surrounding skin.

Figure 1

Black discoloration over medial side of third toe and a traditional silver toe ring in second toe of left foot. Plantar hyperkeratosis is also seen on surrounding skin

A black marking over skin by certain metals is called as black dermographism (BD). It is a misnomer as this is not a physiologic phenomenon.[1] BD has been demonstrated by various metals such as gold, silver, nickel, zinc, lead, and aluminum under certain conditions.[2] It is commonly observed with jewelry like rings, necklaces, metallic wrist bands, etc.[3] Urbach and Pillsbury stated that pigmentation of BD could be demonstrated over skin, paper, cloth, or wood with certain inorganic powders.[4] There are two mechanisms suggested for formation of BD. The physical mechanism states that metals in the presence of certain powders which are hard in nature, abrade the metals, and deposit the metal particles over the skin. These very small metal particles absorb light and do not reflect it, hence appear as dark black.[5] We believe, in our case household detergents, environmental dust, or application of talcum powder after wet work may have played a role in the induction of BD. In general, it is difficult to produce BD on naturally oily skin than dry skin. When slight pressure is exerted on rough dry skin, the metals are more easily rubbed off to produce fine particles which induce the reaction. We believe in our patient when her wet work was over, stratum corneum of hyperkeratotic plantar skin of her toes dried off, and a similar mechanism might have come into play.[4] Another mechanism suggests the role of chemicals from body sweat which react with salts of jewelry metals. Rapson demonstrated that body sweat which contains sulfur containing amino acids such as L-cysteine, glutathione, and D-penicillamine react with the gold, producing black deposits.[2]

Pigmentation due to BD may be alarming, especially in those who are unaware of it. It could be cosmetically unacceptable, as it happened in our patient. In certain communities of India, there is a tradition of wearing silver rings in the toes following marriage and it is said to be a symbol of married status, especially in Hindu women. The patient should be reassured and explained the benign nature of condition. BD can be prevented by avoiding contact of powders with metals. We discouraged our patient from using talcum powder. The usage of protective footwear and socks may be useful. Normally, pigmentation of BD can be removed with repeated washing the area with soap and water. Ethyl alcohol or benzene also can be used to remove BD.[4]

Our case illustrates a distinct morphological presentation due to silver ornaments and its relevance. It also illustrates that the knowledge of cultural practices is important in making a dermatological diagnosis.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that name and initial will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

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Nil.

Conflicts of interest

There are no conflicts of interest.