Warts are a common dermatological concern that afflicts individuals of all ages. In this article, we will delve into the microscopic details of different types of warts, shedding light on their distinctive characteristics as observed through histopathological examination.
Common Warts (Verruca Vulgaris)
Common warts, or verruca vulgaris, exhibit a range of notable histopathological features. These include hyperkeratosis, papillomatosis, and hypergranulosis, contributing to the classic appearance of these growths.
Parakeratosis, especially over dermal papillae, is a common finding. Intracorneal hemorrhage and vacuolated superficial keratinocytes with pyknotic raisin-like nuclei, known as koilocytes (figure 1), can be observed.
However, it’s important to note that koilocytes may not be present in older lesions and are not a necessity for diagnosis. Another characteristic is the inward bending of rete ridges at the borders of the lesion, creating a “toeing in” effect. Furthermore, dilated capillaries in dermal papillae result in the wart projecting above the plane of the epidermis.
Figure 1: Koilocytes-vacuolated superficial keratinocytes with pyknotic raisin-like nuclei (H and E, 1000x)
Palmar/Plantar Warts (Verruca Palmaris and Verruca Plantaris)
Palmar and plantar warts share similarities with verruca vulgaris in terms of histopathology. The clinical distinction between these warts is primarily based on their location. Notably, these warts exhibit endophytic growth, with a larger portion of the lesion residing beneath the plane of the epidermis (figure 2).
Figure 2: Massive hyperkeratosis, papillomatosis, and hypergranulosis in plantar warts (H and E, 400x)
Myrmecia warts present marked acanthosis and large eosinophilic intracytoplasmic inclusion bodies, setting them apart histopathologically.
Plane Warts (Verrucae Planae)
Plane warts display acanthosis and hyperkeratosis without papillomatosis or parakeratosis. An intriguing feature is the vacuolization of the cells in the upper stratum spinosum and stratum granulosum, along with the presence of dyskeratotic keratinocytes.
Condyloma Acuminatum (Venereal/Genital Warts)
These warts exhibit a more massive acanthosis with bulbous rete ridges. Koilocytes are commonly found in the upper spinous layer, and parakeratosis is often observed in the valleys of the epithelium, known as crypt parakeratosis.
Epidermodysplasia verruciformis is characterized by hyperkeratosis, hypergranulosis, and acanthosis. Small nests of large cells with pale blue-gray cytoplasm, clear nuclei, and perinuclear halos are often present, and in some cases, it may evolve into squamous cell carcinoma.
The most crucial histopathological feature to remember when examining warts is the presence of koilocytes. Koilocytes are vacuolated superficial keratinocytes with pyknotic raisin-like nuclei and are a defining characteristic of many wart types.