An ulcerated plaque with erythematous indurated borders

This young man had several month history of developing a non healing ulcerated lesion with erythematous, indurated borders on the left arm. What would be the differential diagnosis?

Sunburn and psoriasiform plaques

This young man developed a severe sunburn. In addition to erythema of the sun-exposed areas, physical examination also revealed psoriasiform plaques on the upper back, shoulders, and arms. There was no personal or family history of psoriasis. Please take a look at these images and share your comments.