日本性感染症学会誌 Journal of Japanese Society for Sexually Transmitted Infections

An 80-year-old Japanese male presented to our department with multiple ulcerous lesions on the buttocks. Prior to the appearance of the lesions on the buttocks, he had been on cetuximab for four months for the treatment of the recurrence of a rectal cancer. We supposed that the lesions were caused by cetuximab, therefore, topical corticosteroid was applied to the lesion. However, there was no improvement. We performed a skin biopsy and the histopathological findings showed multinucleated keratinocytes with inclusion bodies in the epidermis associated with infiltration of lymphoid cells in the dermis. A swab sample of the biopsy of the lesion using the loop-mediated isothermal amplification, was positive for herpes simplex virus-2 DNA. Treatment with cetuximab was discontinued and oral valaciclovir (500 mg twice daily) was administrated for 14 days. The skin lesions of the patient had healed with pigmentation 45 days after the initiation of this treatment. Treatment with cetuximab was then restarted; however, a few months later, the lesions flared up. Oral valaciclovir (500 mg twice daily) was then administrated for 14 days followed by suppressive therapy with oral valaciclovir (500 mg daily). No recurrence was observed after the suppressive therapy.