Ixekizumab Type I Allergy in a Patient With Psoriasis

ABSTRACT A 52‐year‐old Caucasian woman was referred for an allergy workup of suspected type I allergy to the interleukin (IL)‐17A inhibitor ixekizumab. Five months after ixekizumab initiation, she suddenly developed intense pruritus and three small wheals at the injection site approximately 30 min after injection, lasting up to 3 days. With each additional application, she experienced a crescendo‐like amplification of skin symptoms. Allergy skin tests with ixekizumab, adalimumab (anti‐TNF‐α), brodalumab (anti‐IL17RA), risankizumab (anti‐IL‐23p19) and tildrakizumab (anti‐IL‐23p19) were performed. Skin prick testing showed positive results for ixekizumab with negative results for all other tested biologics. Intradermal testing, confirmed positive reactivity for ixekizumab already at a lower concentration. Intradermal testing was also positive for undiluted brodalumab, risankizumab and tildrakizumab. Allergy skin tests confirmed type I allergy to ixekizumab and suggested cross‐sensitization to brodalumab, risankizumab and tildrakizumab, for which the patient was treatment‐naïve.