Injection site reactions are well recognized in patients treated with etanercept. Previous reports describe histologic findings of a cell-mediated T(H)1 reaction, with CD8+ T cells composing the majority of the dermal infiltrate.
A pruritic, erythematous, edematous patch occurred on the right thigh of a 57-year-old white woman treated for rheumatoid arthritis within 12 to 24 hours after her second dose of subcutaneous etanercept. The patient had a similar reaction to adalimumab injection 2 weeks prior to presentation. While benzyl alcohol is present in the etanercept preparation, and mannitol in both drugs, dermal injection revealed no reaction to these additives. Biopsy specimens from the etanercept injection site demonstrated papillary dermal edema accompanied by a brisk polymorphous infiltrate with a predominance of eosinophils and scattered flame figures.
Histologic features of eosinophilic cellulitis as a response to etanercept have not been reported to date. Although most injection site reactions contain T cells and represent a T(H)1 immune response, the findings we report suggest a T(H)2-mediated phenomenon.