Distal toxic acral erythema and mucositis secondary to 6-mercaptopurine in a thiopurine methyltransferase "super shunter"

Toxic erythema of chemotherapy is a broad but useful diagnosis used to summate the non-infectious, non-allergic, and reproducible reaction of certain chemotherapeutics. Due to overlapping chemotherapy side effects and often multiple drug exposures, identification of a singular culprit drug is challenging for dermatologists. Herein, we report a patient with 6-mercaptopurine (6-MP) toxic erythema confirmed via toxic metabolite markers secondary to increased levels of thiopurine methyltransferase activity, or so called "super shunting." Consulting dermatologists should be aware of "super shunting" in pediatric patients and consider testing for metabolites in patients with toxic acral erythema and mucositis in the setting of 6-MP.