Is it atopic eczema or contact dermatitis?
It can be difficult to distinguish a flare in atopic eczema from chronic allergic contact dermatitis in individuals who may display both processes concurrently. The primary clue to the diagnosis is the peculiar localization of the rash, as evidenced by the cases we have described.
Patch testing is not required for diagnosis
Nickel contact dermatitis is often suspected when patients present with an acute or sub-acute eruption characterized by erythema, vesicles, and scaling in a distribution corresponding to a metal contact allergen. Nickel allergy is one of the few types of allergic contact dermatitis where the history of exposure along with the signs and symptoms are so distinctive that patch testing is often not required.
Amelioration of the rash associated with the withdrawal of the contactant serves as adequate confirmation of the diagnosis in many cases. A DMG test is a simple, inexpensive way to determine whether the object in question contains nickel. It can be used in the physician’s office or by the patient at home. Therefore, in some clinical situations, as in the presented cases, it is appropriate to make a presumptive diagnosis of nickel dermatitis, confirm the presence of nickel with a DMG test, remove the off ending metal item, treat with topical anti-inflammatory medications, and confirm the diagnosis by monitoring the patient’s response.
When patients do not respond to withdrawal of the suspected allergen and anti-inflammatory treatment, when multiple allergens are suspected, or when a definitive diagnosis is required for legal purposes, patch testing with nickel can confirm the diagnosis. In some cases, when the distribution of the rash is not distinctive, patch test screening may elicit a positive test to nickel that prompts the physician to investigate the source of the exposure.