This specimen from the leg of a 65-year-old man was submitted to rule out basal cell carcinoma. This is a typical presentation and clinical diagnosis for clear cell acanthomas, as they are often red-brown with telangiectasias. The etiology is unclear, with some authors proposing it is a neoplasm while others favor an inflammatory condition. Giant forms have been described. On histology, a collarette is often present, as shown here. The cells are monotonous and bland. They have a clear look to their cytoplasm from the presence of glycogen, which can be demonstrated by a PAS stain (and eliminated with diastase) or electron microscopy. The differential diagnosis includes seborrheic keratosis, Bowen disease, and poroma. The distinguishing features include the sharp demarcation of clear cells with the adjacent epidermis, absence of cytologic atypia, and the typical presence of inflammatory cells.
At higher power of the same lesion, there is an abrupt change in the epidermis at the edge of the lesion. The cells are clearly keratinocytes, as intercellular bridges are evident. Their cytoplasm is pale (glycogenated). Significant atypia is not present. Overlying the lesion is parakeratotic scale, and few inflammatory cells percolate through.