Tinea versicolor often manifests with tan, slightly scaly patches on the trunk and extremities. On histologic examination, tinea versicolor demonstrates multiple hyphae and spores in the stratum corneum, which can be highlighted with PAS staining.
Epidermodysplasia verruciformis is a genetic disorder that predisposes to human papillomavirus (HPV) infection by multiple strains, including HPV-3, HPV-5, and HPV-8. Epidermodysplasia verruciformis usually demonstrates large cells in the granular and spinous layers. The cells have a blue-gray cytoplasm, a clear nucleoplasm, and a perinuclear halo.
Although lichen planus can have multiple flat-topped papules, the papules are usually violaceous in color and pruritic. On biopsy, lichen planus demonstrates a bandlike lymphocytic inflammatory infiltrate in the superficial dermis, associated with epidermal hyperkeratosis, wedge-shaped hypergranulosis, and peg-shaped rete ridges. There is basal layer vacuolar alteration and colloid body formation owing to degenerated keratinocytes.
Verrucae plana (flat warts) are caused by HPV infection, usually HPV-3 and HPV-10. They demonstrate basket-weave hyperkeratosis and acanthosis, with diffuse vacuolization of the cells of the granular and upper spinous layers and pyknotic nuclei, creating a “bird’s eye” appearance of the cells. Hypergranulosis is common.
Verrucae vulgaris are also caused by HPV infection. However, in contrast to verrucae plana, verrucae vulgaris classically demonstrate marked epidermal acanthosis and hyperkeratosis, with columns of parakeratosis overlying papillomatous projections. The valleys of the projections show vacuolated, koilocytic cells with pyknotic nuclei and clumping of keratohyaline granules.