Definition

Human papillomaviruses (HPVs) are epitheliotropic double-stranded DNA viruses that infect keratinocytes and induce epithelial proliferation, producing benign and malignant mucocutaneous lesions.

HPV-associated disorders include:

• Common warts (verruca vulgaris)

• Plantar warts

• Flat warts

• Filiform warts

• Genital warts (condyloma acuminatum)

• Epidermodysplasia verruciformis (EV)

• Focal epithelial hyperplasia (Heck disease)

• Verrucous carcinoma / Buschke–Löwenstein tumor

Virology

HPV is:

• Non-enveloped

• Circular double-stranded DNA virus

• Member of Papillomaviridae family

Virus infects:

• Basal keratinocytes

Replication depends on:

• Keratinocyte differentiation

HPV Classification

Over 200 HPV types exist.

Cutaneous Low-Risk Types

Commonly:

• HPV 1, 2, 4, 27, 57

Mucosal Low-Risk Types

• HPV 6, 11

Associated with:

• Condyloma acuminatum

High-Risk Oncogenic Types

• HPV 16, 18, 31, 33

Associated with:

• Squamous cell carcinoma

• Cervical neoplasia

• Anogenital malignancy

• Oropharyngeal carcinoma

FOUNDATIONS (First Principles)

Normal Histology Relevant to HPV

Epidermis

Composed of:

• Basal layer

• Spinous layer

• Granular layer

• Cornified layer

Normal keratinocyte maturation proceeds upward from basal layer to stratum corneum.

Basal Keratinocytes

Basal cells:

• Are mitotically active

• Attach to basement membrane

• Replenish epidermis

HPV specifically infects these cells.

Keratinization

Normal keratinization produces:

• Ordered maturation

• Loss of nuclei in stratum corneum

HPV disrupts normal differentiation.

INITIATING EVENT

The initiating event is:

• HPV inoculation into basal keratinocytes through microtrauma

Virus gains access through:

• Disrupted epidermal barrier

Early viral genes:

• E6

• E7

Alter host cell cycle regulation.

PATHOGENESIS (Cause → Effect Chain)

Step 1: Viral Entry

HPV enters basal keratinocytes through microscopic trauma.

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Step 2: Episomal Viral Persistence

Viral DNA remains episomal in nucleus.

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Step 3: Keratinocyte Proliferation

Viral proteins stimulate cell cycle progression.

E6 and E7 interfere with:

• p53

• Retinoblastoma (Rb) protein

Especially in oncogenic HPV types.

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Step 4: Abnormal Keratinization

As infected keratinocytes differentiate upward:

• Viral replication increases

• Cytopathic changes develop

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Step 5: Papillomatous Epidermal Hyperplasia

Produces:

• Verrucous surface

• Hyperkeratosis

• Acanthosis

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Step 6: Viral Shedding

Mature virions are released from superficial epidermis.

No viremia occurs.

HISTOPATHOLOGY EXPLAINED

Core Histological Pattern of HPV Infection

HPV infection→Keratinocyte proliferation→Papillomatous epidermal hyperplasiaHPV infection→Keratinocyte proliferation→Papillomatous epidermal hyperplasia

Fundamental Histological Features

1. Papillomatosis

Papillomatosis means:

• Upward projection of epidermis forming finger-like undulations

Why?

• HPV stimulates epidermal proliferation

Clinically produces:

• Verrucous surface

2. Hyperkeratosis

Thickened stratum corneum.

Why?

• Increased keratinocyte turnover

3. Acanthosis

Diffuse epidermal hyperplasia.

“Acanthe” = thorn/spinous layer.

Refers mainly to:

• Expansion of stratum spinosum

4. Koilocytosis

Most characteristic cytopathic effect.

Koilocytes are:

• Enlarged keratinocytes

• Perinuclear clearing (halo)

• Irregular hyperchromatic nuclei

Why does halo form?

• Viral cytopathic vacuolization of cytoplasm

Seen mainly in:

• Upper epidermis

Very important in:

• Genital HPV infection

5. Elongated Rete Ridges

Rete ridges may:

• Bend inward

• Converge centrally

Characteristic in common warts.

6. Dilated Capillaries

Capillaries within dermal papillae become enlarged.

Clinically:

• Black dots in warts represent thrombosed capillaries

TEMPORAL EVOLUTION

Early Lesions

• Mild acanthosis

• Subtle koilocytosis

Mature Lesions

• Marked papillomatosis

• Hyperkeratosis

• Viral cytopathic change

Regressing Lesions

• Lymphocytic infiltrate

• Keratinocyte apoptosis

• Reduced viral changes

Spontaneous regression is T-cell mediated.

NAMING LOGIC & TERMINOLOGY

“Koilocyte”

Derived from Greek “koilos” meaning hollow.

Refers to:

• Perinuclear vacuolated appearance.

“Papillomatosis”

Refers to:

• Papillary epidermal projections.

“Verruca”

Means wart.

“Condyloma”

Means knuckle-like growth.

STAINING & MARKERS

H&E

Usually sufficient for diagnosis.

Shows:

• Koilocytosis

• Papillomatosis

• Hyperkeratosis

HPV Detection

PCR

Most sensitive method for HPV typing.

In Situ Hybridization

Localizes viral DNA in tissue.

p16 Immunostaining

Surrogate marker for high-risk HPV.

Why positive?

• High-risk E7 inactivates Rb

• Causes p16 overexpression

Important in:

• HPV-associated dysplasia/carcinoma

COMMON WARTS (VERRUCA VULGARIS)

Clinical Features

Usually caused by:

• HPV 2, 4

Appear as:

• Hyperkeratotic papules

• Rough surface

• Black puncta

Common sites:

• Hands

• Fingers

• Periungual skin

Histopathology

Features:

• Hyperkeratosis

• Papillomatosis

• Hypergranulosis

• Inward bending rete ridges

Characteristic:

• Coarse keratohyalin granules

Koilocytosis present.

Differential Diagnosis

• Seborrheic keratosis

• Corn/callus

• Verrucous carcinoma

PLANTAR WARTS

Clinical Features

Usually caused by:

• HPV 1

Occur on:

• Soles

Pressure forces lesion inward.

Features:

• Pain on lateral pressure

• Thrombosed capillaries

Histology

Endophytic growth pattern common.

May show:

• Massive hyperkeratosis

• Hemorrhage within stratum corneum

FLAT WARTS (VERRUCA PLANA)

Clinical Features

Usually caused by:

• HPV 3, 10

Appear as:

• Flat-topped smooth papules

• Skin-colored or brown

Common on:

• Face

• Dorsal hands

• Shins

Koebner phenomenon may occur.

Histopathology

Subtle changes:

• Mild acanthosis

• Basket-weave hyperkeratosis

• Koilocytosis

“Bird’s-eye cells” may be seen:

• Vacuolated keratinocytes with central basophilic nucleus

FILIFORM WARTS

Clinical Features

Finger-like projections.

Common on:

• Face

• Eyelids

• Beard area

Histopathology

Marked papillomatosis with thin elongated projections.

GENITAL WARTS (CONDYLOMA ACUMINATUM)

Etiology

Usually:

• HPV 6, 11

Clinical Features

Soft verrucous papules or plaques involving:

• Vulva

• Penis

• Perianal skin

• Perineum

Can coalesce into large masses.

Histopathology

Features:

• Papillomatosis

• Acanthosis

• Koilocytosis

Koilocytosis is especially prominent.

Differential Diagnosis

• Condyloma lata (syphilis)

• Bowenoid papulosis

• SCC

EPIDERMODYSPLASIA VERRUCIFORMIS (EV)

Definition

Rare inherited disorder characterized by abnormal susceptibility to specific HPV types.

Associated HPV types:

• HPV 5

• HPV 8

High risk of cutaneous SCC.

Genetics

Usually due to mutations in:

• EVER1/TMC6

• EVER2/TMC8

Defective cellular immunity against HPV.

Clinical Features

Childhood onset.

Features:

• Flat wart-like lesions

• Pityriasis versicolor-like macules

Sun-exposed areas affected.

Histopathology

Characteristic enlarged keratinocytes with:

• Pale blue-gray cytoplasm

• Large nuclei

Prominent in upper epidermis.

Malignant Transformation

High risk of SCC in sun-exposed skin.

Especially with HPV 5 and 8.

FOCAL EPITHELIAL HYPERPLASIA (HECK DISEASE)

Etiology

Associated with:

• HPV 13

• HPV 32

Clinical Features

Multiple soft papules in oral cavity.

Common in:

• Children

• Certain ethnic groups

Sites:

• Lips

• Buccal mucosa

• Tongue

Histopathology

Features:

• Acanthosis

• Broad rete ridges

• Mitosoid cells

“Mitosoid cells”:

• Altered nuclei resembling mitotic figures

Characteristic feature.

VERRUCOUS CARCINOMA / BUSCHKE–LÖWENSTEIN TUMOR

Definition

Low-grade well-differentiated SCC with pushing invasion and verrucous architecture.

Buschke–Löwenstein tumor:

• Giant condyloma acuminatum variant

Associated with:

• HPV 6, 11

Clinical Features

Large:

• Exophytic

• Cauliflower-like

• Locally destructive masses

Usually anogenital.

Histopathology

Features:

• Massive papillomatosis

• Hyperkeratosis

• Broad pushing rete ridges

Minimal cytologic atypia despite invasive growth.

Important distinction:

• Pushing rather than infiltrative invasion

Differential Diagnosis

Condyloma Acuminatum

Smaller and non-invasive.

Conventional SCC

Shows:

• Marked atypia

• Infiltrative growth

CLINICO-PATHOLOGICAL CORRELATION

Why do warts feel rough?

Due to:

• Hyperkeratosis

• Papillomatosis

Why do plantar warts hurt?

Pressure forces lesion inward against dermal nerves.

Why are black dots seen?

Thrombosed capillaries in dermal papillae.

Why do genital warts appear soft?

Less compact keratinization in moist mucosal sites.

Why does EV predispose to SCC?

Defective HPV immunity permits persistent oncogenic infection.

UV radiation synergizes with HPV-mediated carcinogenesis.

Differential Diagnosis of Viral Warts

• Seborrheic keratosis

• Corn/callus

• Molluscum contagiosum

• Hypertrophic lichen planus

• Verrucous carcinoma

• Condyloma lata

Management

General Principles

Many warts regress spontaneously due to cell-mediated immunity.

Treatment depends on:

• Site

• Number

• Symptoms

• Immunosuppression

Destructive Therapies

Cryotherapy

Most commonly used.

Causes:

• Cellular destruction

• Immune activation

Salicylic Acid

Keratolytic.

Useful for:

• Common warts

• Plantar warts

Curettage & Electrocautery

Useful for isolated lesions.

Laser Therapy

For resistant lesions.

Immunomodulatory Therapies

Imiquimod

Stimulates:

• Toll-like receptor 7

• Interferon production

Especially useful in genital warts.

Intralesional Immunotherapy

Examples:

• Candida antigen

• MMR vaccine

Stimulates cell-mediated immunity.

Antiviral/Cytotoxic Agents

Podophyllotoxin

For genital warts.

Inhibits mitosis.

Trichloroacetic Acid

Chemical destruction.

HPV Vaccination

Prevents infection with major oncogenic and low-risk types.

Vaccines cover:

• HPV 6/11

• HPV 16/18

• Additional high-risk strains

Prognosis

Common Warts

Often regress spontaneously.

Genital HPV

Recurrence common.

EV

High risk of cutaneous SCC.

Buschke–Löwenstein Tumor

Locally aggressive with recurrence tendency.

EXAM-FOCUSED INSIGHTS

• Koilocytosis is the hallmark cytopathic effect of HPV.

• HPV infects basal keratinocytes through microtrauma.

• Common warts show inward bending rete ridges.

• Plantar warts are painful on lateral compression.

• Flat warts are associated with HPV 3 and 10.

• Condyloma acuminatum is usually caused by HPV 6 and 11.

• High-risk HPV types include 16 and 18.

• EV predisposes to SCC due to defective HPV immunity.

• Heck disease shows mitosoid cells.

• Verrucous carcinoma shows pushing invasion with minimal atypia.

• p16 positivity suggests high-risk HPV-associated neoplasia.

MUST-KNOW BOARD EXAM QUESTIONS

1. What is the hallmark cytopathic effect of HPV infection?

Koilocytosis.

2. Which cells are initially infected by HPV?

Basal keratinocytes.

3. Which HPV types commonly cause common warts?

HPV 2 and 4.

4. Which HPV type commonly causes plantar warts?

HPV 1.

5. Which HPV types commonly cause genital warts?

HPV 6 and 11.

6. Which HPV types are high-risk oncogenic strains?

HPV 16 and 18.

7. What are koilocytes?

Keratinocytes with perinuclear halo and hyperchromatic irregular nuclei.

8. What causes black dots in warts?

Thrombosed capillaries.

9. Which disorder predisposes to widespread HPV infection and SCC?

Epidermodysplasia verruciformis.

10. Which genes are mutated in epidermodysplasia verruciformis?

EVER1/TMC6 and EVER2/TMC8.

11. What are mitosoid cells characteristic of?

Heck disease.

12. Which marker is overexpressed in high-risk HPV-associated lesions?

p16.

13. What is Buschke–Löwenstein tumor?

Giant condyloma acuminatum/verrucous carcinoma.

14. What type of invasion is seen in verrucous carcinoma?

Broad pushing invasion.

15. Why do warts regress spontaneously?

Cell-mediated immune response against HPV-infected keratinocytes.