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Dermatophytid Reaction

by Denise M. Aaron, MD

Dermatophytid reaction is an inflammatory reaction to dermatophytosis at a cutaneous site distant from the primary infection.

Dermatophytid (identity or id) reactions are protean; they are not related to localized growth of the fungus but rather are an inflammatory reaction to a dermatophytosis (see Overview of Dermatophytoses) elsewhere on the body. Lesions are typically pruritic but may manifest as

  • Vesicular eruptions on the hands and feet

  • Follicular papules

  • Erysipelas-like plaques

  • Erythema nodosum

  • Erythema annulare centrifugum

  • Urticaria

Distribution may be extensive.

Diagnosis is by potassium hydroxide wet mounts that are negative at the site of the id reaction and positive at the distant site of dermatophyte infection.

Treatment of the primary infection cures dermatophytid; pending cure, topical corticosteroids and/or antipruritics (eg, hydroxyzine 25 mg po qid) can be used to relieve symptoms.

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