Viral Warts
Summary
Viral Warts are ubiquitous, benign cutaneous proliferations caused by infection of keratinocytes with Human Papillomavirus (HPV). They can affect any epithelial surface but predominantly occur on the hands (Common Warts) and feet (Plantar Warts/Verrucae). Though usually self-limiting, they can be painful (especially plantar) and cosmetically distressing. Treatment is often destructive (Acid, Cryotherapy) and recurrence is common. [1,2]
Clinical Pearls
The "Black Dot" Sign: Pathognomonic for viral warts. If you pare down the hard skin of a plantar lesion with a scalpel, you will see tiny black dots. These are thrombosed capillaries feeding the wart.
- Corns (Clavi): Have a translucent glassy core without black dots.
- Callus: Just thickened skin, no core or dots.
The Transplant Patient: Patients on long-term immunosuppression (organ transplant) are at HUGE risk of warts transforming into Squamous Cell Carcinoma (SCC). Any changing/ulcerated wart in a transplant patient must be biopsied aggressively.
Mosaic Warts: A cluster of many small warts that coalesce into a large plaque on the sole of the foot. notoriously difficult to treat.
Demographics
- Prevalence: 10-20% of school-aged children. 3-5% of adults.
- Transmission: Direct contact or fomites (Swimming pool floors).
- Incubation: Long (1-6 months+).
Etiology (HPV Types)
- Common Warts: HPV 2, 4, 27, 29.
- Plantar Warts: HPV 1.
- Plane Warts: HPV 3, 10.
- Genital Warts: HPV 6, 11 (Low risk), 16, 18 (High risk).
Mechanism
- Innoculation: HPV enters basal keratinocytes through micro-abrasions.
- Proliferation: Virus stimulates rapid cell division (Hyperplasia) and thickening of the stratum corneum (Hyperkeratosis).
- Immune Evasion: The virus lives in the upper epidermis, "hidden" from the host immune system (no blood stream contact). Spontaneous resolution occurs only when the immune system finally recognises viral antigens.
| Condition | Features |
|---|---|
| Viral Wart | Black dots (Thrombosed capillaries). Disappears on stretching skin. |
| Corn (Clavus) | Pressure point. Glassy core. Painful on direct pressure. |
| Callus | Diffuse thickening. |
| Squamous Cell Carcinoma | Ulcerated, rapidly growing, fleshy border. |
| Molluscum Contagiosum | Pearly papules with central umbilication. (Poxvirus). |
Variants
- Common Warts (Verruca Vulgaris): Rough, hyperkeratotic "cauliflower" papules. Hands, knees, fingers.
- Plantar Warts (Verrucas): Soles of feet. Flush with surface (pushed in by weight). Surrounded by callus. Painful on walking.
- Plane Warts (Verruca Plana): Flat-topped, smooth, skin-coloured. Face/shins. Often spread by shaving (Koebner phenomenon).
- Filiform Warts: Spiky, finger-like projections. Face/Eyelids.
Diagnosis
- Clinical: Usually obvious.
- Dermoscopy: Shows thrombosed capillaries (red/black dots) / Frogspawn appearance.
- Paring: Removal of hyperkeratotic layer to reveal dots.
Histology (Biopsy)
- Only needed if diagnostic doubt or suspect malignancy (SCC).
- Shows: Hyperkeratosis, papillomatosis, koilocytes (HPV infected cells).
Management Algorithm
CLINICAL DIAGNOSIS OF WARTS
↓
IS TREATMENT NECESSARY?
(Painful? Embarrassing? Spreading?)
┌─────────┴─────────┐
NO YES
↓ ↓
OBSERVATION FIRST LINE
(Wait & See) Topical Salicylic
Resolves in Acid (Daily)
6-24 months for 12 weeks
(Paint & File)
↓
SECOND LINE
Cryotherapy
(Liquid Nitrogen)
Every 2-3 weeks
↓
THIRD LINE
(Dermatology)
• Immunotherapy
• Curettage
• Laser
1. Topical Therapy (Keratolytics)
- Salicylic Acid (15-50%): E.g., Salactol, Bazuka.
- Regimen: Soak foot -> File down hard skin -> Apply paint. Repeat daily.
- Efficacy: 75% cure rate (equal to or better than cryo for plantar warts).
2. Cryotherapy
- Liquid Nitrogen: Freezes cell water -> Lysis.
- Application: 10-20 seconds freeze (until ice halo). Painful blister forms.
- Repeat: Every 2-3 weeks.
- Note: Less effective on thick plantar skin.
3. Other Treatments
- Duct Tape Occlusion: Evidence is conflicting, but harmless.
- Imiquimod: Immune response modifier (used for genital/plane warts).
- Procedures: Curettage/Cautery (scarring risk), Pulsed Dye Laser.
- Pain: Particularly plantar warts on pressure points.
- Cosmetic: Social stigma ("Wart hands").
- Resolution: Can leave no trace or mild scarring.
- Malignancy: Verrucous Carcinoma (rare low grade SCC).
- Natural History:
- Children: 50% gone in 1 year, 70% in 2 years.
- Adults: Can be persistent/recalcitrant (years).
- Recurrence: Common (latent virus in adjacent skin).
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Cutaneous Warts | BAD (Br. Assoc. Derm) | Salicylic acid is first line. Cryotherapy second. |
Landmark Evidence
1. Cochrane Review (Sterling et al)
- Concluded that Topical Salicylic Acid significantly increases clearance rate compared to placebo.
- Cryotherapy was no more effective than salicylic acid for simple hand warts and less effective for plantar warts, but much more painful/expensive.
What are warts?
They represent a harmless viral infection of the top layer of skin. The virus (HPV) makes the skin grow too fast, forming a rough lump.
Did I catch it from a toad?
No. You caught it from direct contact with someone else's wart, or from a wet floor (like a swimming pool) where the virus can survive.
How do I get rid of it?
Patience is the best medicine. In children, they almost always go away on their own without scarring. If they are painful or annoying, you can use "wart paints" from the pharmacy. You must use them every night for 3 months to work. You have to file the dead skin off first. Freezing (by a doctor) hurts a lot and doesn't always work better than the paint.
Primary Sources
- Sterling JC, et al. British Association of Dermatologists' guidelines for the management of cutaneous warts. Br J Dermatol. 2014.
- Kwok CS, et al. Topical treatments for cutaneous warts. Cochrane Database Syst Rev. 2011.
Common Exam Questions
- Diagnosis: "Child with extensive warts on hands?"
- Answer: Common viral warts. Reassure.
- Safety: "Wart on face - treat?"
- Answer: Do NOT use Salicylic acid or Cryo on face (scarring). Refer (or use mild retinoids).
- Pathology: "Transplant patient with warts?"
- Answer: High suspicion for SCC transformation.
- Differentiation: "Black dots in lesion?"
- Answer: Viral Wart (thrombosed capillaries).
Viva Points
- Structure: Warts distort the skin lines (dermatoglyphics). When a wart heals, the fingerprints return.
- Koebner Phenomenon: Linear spread of warts along a scratch mark or shave line.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.