AN ITCHY LOCALIZED ERUPTION

These lesions are best described as chronic and eczematous. Such a localized problem suggests an exogenous aetiology (the photograph that is Fig. 7.1 provides a clue). The most likely diagnosis is allergic contact dermatitis (ACD), although it can be very diffi-cult to differentiate clinically between ACD and irritant contact dermatitis. Occasionally, psoriasis may present with a single plaque, particularly at a site of trauma (Koebner’s effect); however, it is rarely as pruritic as this eruption. Atopic dermatitis is usually a more generalized and diffuse eruption; however discoid or nummular eczema is characterized by fairly well defined, coin-shaped, intensely pruritic inflamed areas of lichenified skin. An inflammatory tinea corporis particularly associated with a zoophilic organism might also be considered. The presentation of contact dermatitis can be varied, including dyspigmentation, pustular lesions, urticaria, atrophy, phototoxic reactions and eczema. It would be appropriate to obtain a skin scraping for mycology investigations. Patch testing (Fig. 7.2) is the diagnostic test to detect sensitization to contact allergens. (Although patch testing is not required for diagnosis; nickel allergy is one of the few types of allergic contact dermatitis where the history of exposure along with the signs and symptoms are quite distinctive.) In fact many patients do not present to medical practitioners as they may well work out the association themselves. If a patch test series confirms the presence of nickel allergy, its relevance to the current eruption should be confirmed. A dimethylglyoxime (DMG) test is a simple, inexpen-sive way to determine whether the object in question contains nickel by a pink colour change. Chromate, palladium and cobalt are commonly found together with nickel and concomitant allergy may coexist. Nickel is a leading cause of allergic contact dermatitis and is responsible for more cases than all other metals combined. Certain occupations with high exposure to nickel, such as cashiers, hairdressers, metal workers, domestic cleaners, food handlers, bar work-ers, and painters, are also at risk for acquiring nickel dermatitis. Patients with atopic eczema are also at increased risk. Sweating may increase the severity of the dermati-tis. Sodium chloride in the sweat causes corrosion of the metal and increases nickel exposure.The management of this case includes removal of the offending nickel-containing belt buckle or trouser rivet and application of topical corticosteroid creams until the erup-tion has resolved. The patient also requires information about his allergy, that is he will always remain allergic to nickel and to both the common and unexpected sources of nickel. Nickel allergy is commonly associated with earrings and jewellery or other body piercing. Nickel can be found in many everyday items – from coins to necklace clasps, from watchbands to eyeglass frames, and tools and utensils used in the workplace and home.

KEY POINTS

• Nickel is the most common allergen detected in patch test clinics worldwide. It is a strong silver-coloured metal that is commonly used in buckles, utensils and coins. It should no longer be present in jewellery purchased within the European Union.

• A useful test to confirm whether a particular item contains nickel is the dimethylglyoxime (DMG) test.

• The management includes treatment of the manifestation and avoidance of direct cutaneous contact with nickel.