The histopathologic specimen demonstrated acanthosis, hyperkeratosis, and mild papillomatosis of the epidermis. A parakeratotic column (cornoid lamella) was noted within the stratum corneum, overlying invagination of the epidermis. The granular layer was absent beneath the column, and focal dyskeratosis was evident. The results of all laboratory investigations, including a complete blood cell count, comprehensive metabolic panels, urinalysis, and tests for human immunodeficiency virus, rapid plasma reagin, and herpes simplex virus, were negative.