Nongenital Warts Workup

Updated: Sep 25, 2020
  • Author: Philip D Shenefelt, MD, MS; Chief Editor: William D James, MD  more...
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Laboratory Studies

The diagnosis of warts is made primarily on the basis of clinical findings. Immunohistochemical detection of HPV structural proteins may confirm the presence of virus in a lesion, but this has a low sensitivity. Viral DNA identification using Southern blot hybridization is a more sensitive and specific technique used to identify the specific HPV type present in tissue. Polymerase chain reaction may be used to amplify viral DNA for testing. Although HPV may be detected in younger lesions, it may not be present in older lesions.



Paring of warts may reveal minute black dots, which represent thrombosed capillaries. Obtain a biopsy if doubt exists regarding the diagnosis.


Histologic Findings

Common warts

Histopathologic features of common warts include digitated epidermal hyperplasia, acanthosis, papillomatosis, compact orthokeratosis, hypergranulosis, dilated tortuous capillaries within the dermal papillae, and vertical tiers of parakeratotic cells with entrapped red blood cells above the tips of the digitations. Elongated rete ridges may point radially toward the center of the lesion. In the granular layer, HPV-infected cells may have coarse keratohyaline granules and vacuoles surrounding wrinkled-appearing nuclei. Koilocytic (vacuolated) cells are pathognomonic for warts.

Deep palmoplantar warts (myrmecia)

Deep palmoplantar warts appear similar to common warts except that most of the lesion lies deep to the plane of the skin surface. This endophytic epidermal growth often has the distinctive feature of polygonal, refractile-appearing, eosinophilic, cytoplasmic inclusions composed of keratin filaments, forming ringlike structures. Basophilic nuclear inclusions and basophilic parakeratotic cells loaded with virions may be in the upper layers of the epidermis.

Flat warts

Flat warts resemble common warts on light microscopy; however, the features tend to be muted. Cells with prominent perinuclear vacuolization around pyknotic, strongly basophilic, centrally located nuclei may be in the granular layer. These may be referred to as "owl's eye cells."

Butcher's warts

Butcher's warts have prominent acanthosis, hyperkeratosis, and papillomatosis. Small vacuolized cells with centrally located shrunken nuclei may be seen in clusters within the granular layer rete ridges.

Filiform warts

Filiform warts may appear similar to common warts but tend to have prominent papillomatosis.

Focal epithelial hyperplasia (Heck disease)

Focal epithelial hyperplasia is characterized by a hyperplastic mucosa with thin parakeratotic stratum corneum, acanthosis, blunting and anastomosis of rete ridges, and pallor of epidermal cells as a result of intracellular edema. Some areas may have prominent keratohyaline granules, and some vacuolated cells may be present.

Cystic warts

A cyst filled with horny material characterizes cystic warts. The wall is composed of basal, squamous, and granular cells. Many of the epithelial cells may have large nuclei and clear cytoplasm with eosinophilic inclusion bodies. The cyst may rupture, resulting in a foreign body granuloma.