Joker Sign After Drooling Radioactive Saliva

A 28-year-old man underwent high-dose radioactive iodine therapy after total thyroidectomy due to papillary thyroid carcinomas. After 2 weeks, a linear reddish line was observed extending from the right corner of the mouth to the cheek, resembling the appearance of the Joker. Through a detailed interview, it was determined that the patient had developed radiation dermatitis because of radioactive saliva drooling while sleeping on one side. Although this is expected to be infrequent, educating patients on avoiding saliva contact with the skin during and after radioactive iodine therapy is crucial due to the potential skin damage and cancer risk.