Acute Generalized Exanthematous Pustulosis With Negative Patch Test and Drug-Induced Lymphocyte Stimulation Test (DLST) Results: A Case Report.

Acute generalized exanthematous pustulosis (AGEP) is a rapid-onset skin disorder characterized by edematous erythema, mainly affecting intertriginous areas and the face, along with sterile, non-follicular pustules. It is most often drug-induced, commonly triggered by antibiotics, anticancer agents, or hydroxychloroquine. Symptoms typically appear within a few days of drug exposure. Histologically, AGEP features spongiform pustules in or beneath the stratum corneum, papillary dermal edema, and perivascular neutrophilic infiltration. Patch testing and drug-induced lymphocyte stimulation test (DLST) are used to identify the causative agent, although both may yield false-negative results. We report a case of AGEP occurring two days after administration of paclitaxel, oral iron, and vonoprazan. All three drugs were discontinued, and the patient responded well to topical corticosteroids and oral prednisolone. Patch tests for all agents were negative. However, based on previous reports of severe vonoprazan-induced drug eruptions and the lack of evidence linking paclitaxel or oral iron to AGEP, vonoprazan was considered the most likely culprit. Since the patient wished to continue cancer treatment, paclitaxel and oral iron were cautiously reintroduced with informed consent and close monitoring. No recurrence occurred, further supporting vonoprazan as the causative agent. This case highlights the limitations of patch testing and DLST in AGEP diagnosis and emphasizes the importance of clinical context and therapeutic priorities in evaluating drug causality. Further studies are needed to standardize AGEP testing protocols and improve diagnostic accuracy.