The term eczema can be ambiguous. Primarily, it is used as a lay term for atopic dermatitis, a type of eczema that is chronic, relapsing, pruritic, inflammatory, and often associated with allergic rhinitis and/or asthma. However, it can also be used to characterize a broad range of eczematous dermatoses with varying etiologies and treatments. Distinguishing atopic dermatitis from other eczematous conditions is essential for accurate diagnosis and management.
Eczematous dermatoses include:
When It’s Not Atopic Dermatitis
Isolated acute rash without atopic history: Atopic dermatitis typically presents with chronic or relapsing features and is associated with a personal or family history of atopy. If the patient presents with a sudden rash and no other atopic features (allergic rhinitis, asthma), consider acute differentials such as:
- Allergic contact dermatitis
- Eczematous drug eruption
- Infections (eg, tinea corporis)
- New-onset dermatoses (eg, psoriasis)
Rash in “double-covered” areas in adults: New adult-onset “eczema” in areas covered by clothing and undergarments (such as beneath the underwear or bra) should raise suspicion for mycosis fungoides, a type of cutaneous T-cell lymphoma (CTCL).
Key considerations:
- Atopic dermatitis rarely begins in adulthood without prior history.
- CTCL often mimics eczema and may require serial biopsies for diagnosis.
- Sparing of exposed areas further argues against atopic dermatitis.
Rash worsens with appropriate treatment: Treatment failure may indicate allergic contact dermatitis (even to ingredients in topical steroids or personal care products) or a drug reaction (especially if rash is widespread). Take a detailed history of exposures and medications.
Bottom Line
Atopic dermatitis is just one subset of eczematous dermatoses. Reconsider the diagnosis when:
- The rash is acute and isolated.
- It appears in atypical adult distributions.
- It worsens with standard treatment.
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