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Contact Dermatitis

»	Name the two pathogenic types of contact dermatitis.
»	Name the two subtypes of irritant contact dermatitis, and describe them.
»	Explain the pathogenesis of allergic contact dermatitis (ACD).
»	Can urticarial reactions occur from contact with a substance?
»	Why is the distribution of a contact dermatitis rash important?
»	List three common misperceptions regarding the location of a contact dermatitis.
»	How is patch testing done?
»	What substances are tested in the standard “screening” patch test?
»	An astute physician should not need to patch test. Right?
»	What is a repeated open application test (ROAT)?
»	What is the differential diagnosis of contact dermatitis?
»	Which is the most common allergen on the standard tray?
»	Is nickel the most common allergen overall?
»	If a change in a skin care product does not lead to clearing of a patient’s rash, does this mean that the original product was not the culprit?
»	How is contact dermatitis managed?

What is the differential diagnosis of contact dermatitis?

Contact dermatitis, with its scaling, erythema, lichenification, and/or vesicles, belongs in the group of eczematous disorders. Other such conditions—atopic dermatitis, nummular eczema, neurodermatitis, stasis dermatitis, seborrheic dermatitis, photodermatoses, dermatophyte infections, drug eruptions, and dyshidrotic eczema (pompholyx)—should always be considered when evaluating a prospective patient for contact dermatitis. A complete history including previous skin diseases, drug and exposure histories, location and course of the eruption, patch testing, and potassium hydroxide tests should help point to the diagnosis of contact dermatitis.

Marks JG, Elsner P, DeLeo VA: Contact and occupational dermatology, ed 3, St Louis, 2002, Mosby, pp 20–25.