Infectious Diseases That Mimic Eczema Before Reaching for Biologics

Conclusions

• Before escalating treatment for presumed atopic dermatitis, clinicians should pause and reconsider whether an infectious mimic is actually present.
• Scabies, tinea, HIV-related eruptions, syphilis, and viral infections can all present like eczema and should be actively excluded when the diagnosis is uncertain or treatment fails.
• Syphilis can itch and can masquerade as eczema, so pruritus does not rule it out.
• A positive RPR in a suspicious rash should prompt confirmation with treponemal testing and sexual history rather than dismissal as a false positive.
• Tinea can look like nummular eczema, and a simple KOH exam can prevent unnecessary biologic therapy.
• Exposure history, such as contact with kittens or other animals, may reveal dermatophyte infection as the true cause of a widespread itchy eruption.
• Scabies should remain a routine part of the differential for intensely pruritic eruptions, including in older adults, because it can be mistaken for severe eczema.
• Persistent ‘eczema’ with pustules or poor response to steroids and antibiotics should raise suspicion for eosinophilic pustular folliculitis and possible HIV infection.
• Eczematous eruptions in immunocompromised patients may be a clue to immune deficiency rather than primary atopic dermatitis.
• Travel to tropical regions with mosquito exposure and new arthralgias should prompt consideration of arboviral infections such as chikungunya.
• The key lesson is that infection and atopic dermatitis can mimic one another, so broadening the differential before using biologics or JAK inhibitors improves diagnostic accuracy and patient care.