Id Reaction (Autoeczematization) Workup

Updated: Jul 10, 2018
  • Author: Matthew P Evans, MD; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

Laboratory workup of id reactions is clearly indicated for dermatophytids. Strict criteria include a proven dermatophyte infection and a positive skin test finding for a group-specific trichophytin antigen. Absence of fungi in the dermatophytid lesions and clearing of the dermatophytid after the fungus is eradicated are necessary to confirm a definitive diagnosis of a dermatophytid reaction.

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Other Tests

Patch testing may be needed to exclude primary or secondary allergic contact dermatitis.

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Procedures

Biopsy for routine hematoxylin and eosin staining may be helpful in excluding noneczematous dermatoses, which may appear morphologically similar to an id reaction.

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Histologic Findings

Histopathology of the typical papulovesicular lesion reveals a superficial perivascular lymphohistiocytic infiltrate with a spongiotic epidermis, often with vesiculation. Small numbers of eosinophils may be present in the dermal infiltrate. By definition, infectious agents should not be found in the specimens.

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