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By Azeen Sadeghian, MD
The term eczema can be quite misleading. Sometimes it is used as a category of various eczematous dermatoses (such as asteatotic eczema [xerotic eczema or eczema craquelé], seborrheic dermatitis, contact dermatitis, and stasis dermatitis) and other times it is used as a lay term for atopic dermatitis. Knowing the difference is key in making an accurate diagnosis and treating your patients.
Below are 3 clues that a rash is not atopic dermatitis:
1. The patient doesn't have anything else going on other than a sudden new rash
The Hanifin Rajka diagnostic standard for atopic dermatitis requires 3 major and 3 minor criteria to be met.
The major criteria include:
In my experience, unless they are very young, patients typically have other stigmata of atopy. And although the flare itself may be sudden, the rash itself is usually not. This should prompt you to consider other acute differential diagnoses such as contact dermatitis, infection, drug reaction, or an eruptive component of a new rash altogether.
2. The rash is in double-covered areas in an adult patient
In general, if you're tempted to label an adult patient as having new atopic dermatitis, then you must first consider cutaneous T-cell lymphoma, particularly if the rash involves "double-covered" areas such as beneath the underwear or bra.
Most patients with atopic dermatitis typically have stigmata of it, even in their childhood, and any new diagnosis of atopic dermatitis in adulthood should raise skepticism. If exposed areas are unaffected, then it is even less likely to be eczema.
Remember: typical areas for atopic dermatitis are typical for a reason. Even dermatologists can be stumped by this. There are even times when one biopsies a patient’s lesion multiple times, even over the course of years, to ensure it's not early CTCL.
3. The rash gets worse with proper treatment
A rash worsening with treatment is a clue that it could be an allergic contact dermatitis if localized or a possible drug reaction if more widespread.
If localized or even sometimes widespread, it is wise to consider allergic contact dermatitis. People can become allergic to many ingredients, even the ingredients used in personal care products or topical steroids. Although contact dermatitis is technically categorized under the umbrella term of “eczema,” for conceptual purposes it is best to view allergic contact dermatitis as its own identity. Keep in mind this is a separate diagnosis from irritant contact dermatitis.
When a rash is widespread, also consider drug reactions. A thorough medication and rash history are imperative when considering this diagnosis.
The bottom line:
Atopic dermatitis is just one form of the various diagnoses that fall under the category of “eczema” and can be difficult to manage. An alternative diagnosis should be considered when the rash worsens despite appropriate treatment, the rash is seen in adults in a double-covered area, and required diagnostic criteria are not met.
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