A 93-year-old man had had multiple brown spots with keratinization on his face, trunk, and extremities for 30 years and was diagnosed with porokeratosis. Some erosions appeared on his brown spots 3 years ago. He was referred to our hospital because of nodular lesions that arose on the erosions. There were multiple brown keratotic plaques on his skin throughout the body with some erosions on the abdomen and two red nodules on the left forearm and the right leg. A histological examination of the brown plaques revealed the formation of cornoid lamellae. At the sites of the erosions and red nodules, the proliferation of atypical keratinocytes in the epidermis and their invasion into the upper dermis were observed. We diagnosed this patient as disseminated superficial porokeratosis with multiple squamous cell carcinoma and Bowen's disease. Some cases of porokeratosis show autosomal-dominant inheritance; however, most cases are sporadic. When we examine a patient with porokeratosis, it is necessary to follow them up regularly and carefully observe them for malignant skin lesions throughout the whole body.
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