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Lack of response of severe steroid‐dependent chronic urticaria to rituximab

by complete reactivation of the old lesions with marked violaceous erythema and oedema within 1 h. The provocation reproduced identical cutaneous and mucosal lesions to the original eruption. The lesions healed within 1 week, leaving residual pigmentation. Upon avoidance of etodolac, no other attack was observed during an 8-month followup. Systemic provocation confirmed the diagnosis of etodolac-induced FDE. Etodolac is an indolacetic acid, and together with other indolacetic acids (e.g. indomethacin, acemetacin, benzydamine), and arylacetic acids (e.g. sulindac, diclofenac), it is an acetic acid NSAID derivative. There is only one published report on etodolac-induced nonpigmenting FDE in the Korean literature, and an observational case in Litt’s Drug Eruption Reference Manual. Crossreactivity between chemically related drugs in FDE is well known, pyrazolones being the most frequently reported crossreacting NSAIDs in FDE. Furthermore, NSAIDs are the main reported group of drugs in polysensitivity reactions seen with two or more chemically unrelated drugs in FDE. Crossreactivity among acetic acid derivatives or polysensitivity to other chemically unrelated NSAIDs has been reported sporadically in allergic contact dermatitis but not in FDE. The results indicated the probable role of the acetic acid group in crossreactivity in allergic contact dermatitis. In our case, however, no crossreactivity was found between etodolac and indomethacin or acemetacin (also indolacetic acids), or diclofenac (arylacetic acid), thus making the role of the acetic acid group as a whole in the hypersensitivity reaction of FDE questionable. Moreover, no polysensitivity among a wide list of structurally unrelated groups of NSAIDs was found. In conclusion, this is a rare case of etodolac-induced pigmenting FDE, in which both crossreactivity and polysensitivity were investigated by topical and oral challenge, but yielded negative results. The identification of the allergenic determinants of FDE inducers in future will help in analysing cross-reactivity and polysensitivity in FDE more thoroughly.