A 24-year-old man with a six-year history of psoriasis vulgaris was referred to the dermatological outpatient clinic of the Complejo Hospitalario de Granada, Granada, Spain, in 2016 with multiple brownish cutaneous lesions of different sizes in the right gluteal region. No previous injuries, comorbid conditions or use of concomitant medications were reported. The patient had been undergoing treatment for psoriasis vulgaris with 45 mg of ustekinumab every three months over the previous eight months after other methods of treatment had failed, including methotrexate, cyclosporine and narrowband ultraviolet B phototherapy. The ustekinumab treatment had since resulted in good control of the psoriasis vulgaris (Psoriasis Area and Severity Index score: 0.8; body surface area: 1; Physician Global Assessment score: 1). However, the gluteal lesions had begun to appear one month after ustekinumab treatment was initiated