Clear Cell Acanthoma on Top of Pre-Existing Psoriatic Plaque: A Rare Case Report

摘要

Clear cell acanthoma (CCA) is an uncommon benign tumour of epithelial cells of the epidermis that usually develops slowly over a period of years. Herein, we present a 50 year old Saudi male who is a known case of psoriasis vulgaris presented with asymptomatic solitary skin lesion on top of one of his psoriatic skin lesions for 18 months. Skin examination showed solitary non scaly blackish soft nodule on top of psoriatic plaque on the right side of the trunk. Punch skin biopsy showed psoriasiform acanthosis that is composed of enlarged pale keratinocytes with presence of melanin pigmentation within the keratinocyes. Periodic-acid–Schiff (PAS) staining was positive. On the basis of the above clinicopathological features, the diagnosis of pigmented variant of CCA was made. The lesion was removed by surgical excision. The pigmented variant of CCA and its occurrence on the trunk as well as its occurrence on top of pre-existing psoriatic plaque are unusual presentation of CCA.