Suspected upadacitinib-associated drug hypersensitivity mimicking disease exacerbation in ulcerative colitis

A woman in her 40s with ulcerative colitis experienced suspected drug hypersensitivity to upadacitinib, which mimicked disease exacerbation. Despite treatment with upadacitinib, her symptoms worsened, and a drug-induced lymphocyte stimulation test showed a 230% stimulation index for upadacitinib. After discontinuing upadacitinib and starting tacrolimus, she achieved rapid remission. This case highlights that drug hypersensitivity to Janus kinase inhibitors like upadacitinib should be considered when clinical deterioration occurs during therapy for ulcerative colitis.