Wart Identification with Dermoscopy: Key Features and Diagnostic Tips

I. Introduction

Warts, caused by the human papillomavirus (HPV), are among the most prevalent benign skin growths encountered in clinical practice. Their presentation can vary widely, from the rough, exophytic common wart to the subtle, flat-topped lesions of verruca plana. This very commonality, however, belies a significant clinical challenge: accurate diagnosis. Many skin lesions can mimic warts, leading to misdiagnosis and, consequently, inappropriate or delayed treatment. For instance, a lesion on the sole of the foot might be mistaken for a simple corn, or a pigmented lesion on the face could be confused with a seborrheic keratosis. This diagnostic uncertainty underscores the need for a more precise, in-office tool to bridge the gap between clinical suspicion and definitive identification.

Enter dermoscopy, a non-invasive imaging technique that has revolutionized clinical dermatology. By using a handheld device with magnification and either polarized or non-polarized light, dermoscopy allows clinicians to visualize subsurface skin structures and vascular patterns invisible to the naked eye. For wart identification, dermoscopy is invaluable. It transforms a seemingly uniform skin bump into a landscape of diagnostic clues. The advent of digital dermoscopy, which involves capturing and storing high-resolution images for comparison over time, has further enhanced this utility, allowing for better documentation and monitoring of lesions. In regions like Hong Kong, where dermatological services are in high demand, a 2022 survey by the Hong Kong Dermatological Society indicated that over 70% of practicing dermatologists now routinely use dermoscopy for evaluating common skin growths, citing a marked improvement in diagnostic confidence for conditions like warts and early seborrheic keratoses. This tool moves diagnosis from a realm of educated guesswork to one of pattern recognition based on specific, reproducible features.

II. Core Dermoscopic Features of Warts

Under dermoscopic examination, warts reveal a constellation of characteristic features that fall into three main categories: vascular patterns, surface architecture, and color/pigmentation. A systematic evaluation of these elements forms the cornerstone of accurate diagnosis.

A. Vascular Patterns:

The vascular patterns are often the most telling signs. Warts, being hyper-proliferative lesions, have an increased and abnormal blood supply.

• Punctate vessels (dots): These appear as tiny, sharply demarcated red or reddish-black dots scattered throughout the lesion. They represent dilated capillaries in the dermal papillae, viewed end-on. This is one of the most frequent and reliable signs of a wart.
• Globular vessels: These present as slightly larger, roundish or looped red structures. They are essentially a variation of the punctate pattern where the capillaries are slightly more tortuous or dilated.
• Hairpin vessels (less common): These are fine, U-shaped or hairpin-like vessels. While more classically associated with seborrheic keratoses, they can occasionally be seen in warts, particularly in more keratotic or older lesions.

B. Surface Architecture:

The surface morphology of a wart under dermoscopy is distinctly irregular.

• Papillary projections: The surface is not smooth but composed of multiple finger-like or mamillated projections, giving it a "cauliflower" or cerebriform appearance. Each papilla often contains a central red dot (the punctate vessel).
• Hyperkeratosis: There is a marked thickening of the stratum corneum, which appears as yellowish-white, amorphous, or scaly areas that can partially obscure the underlying structures.
• Fissures: Cracks or clefts are commonly seen on the surface, especially in older or weight-bearing warts like plantar warts. These fissures can be deep and may sometimes bleed.

C. Color and Pigmentation:

The color palette of a wart is typically a mix of non-pigmented hues.

• Yellowish hue: A background yellowish or yellow-white color is very common, resulting from the compact hyperkeratosis.
• Black dots (thrombosed capillaries): These are a pathognomonic feature. They appear as small, sharply outlined black dots or "pepper-like" granules. They represent capillaries that have thrombosed due to the pressure of the overlying hyperkeratosis. Their presence is a strong indicator of a viral wart.
• Whitish scales: Loose, whitish scales are often scattered across the surface, contributing to the overall irregular and "dirty" appearance of the lesion.

Examining a wart under dermoscopy thus involves piecing together these features: looking for the papillary structures dotted with red or black points, set against a yellowish, scaly background with fissures.

III. Dermoscopic Signs by Wart Type

While the core features are shared, different clinical types of warts can have subtle dermoscopic variations that aid in their specific identification.

A. Common Warts (Verruca vulgaris):

Typically found on the hands, fingers, and knees, common warts are the archetype. Dermoscopically, they exhibit pronounced papillary projections, creating a highly irregular, exophytic surface. The vascular pattern is dominated by clustered punctate vessels, often with one red dot crowning each papilla. Thrombosed capillaries (black dots) are frequently interspersed. The hyperkeratosis is significant, giving a thick, yellowish cloak to the lesion.

B. Plantar Warts (Verruca plantaris):

Located on the soles of the feet, these warts are pressed inward by body weight (endophytic). Their dermoscopic appearance is distinctive. The surface often has a thick, homogenous, callus-like (tylotic) appearance of compact yellow keratin. Upon careful inspection, especially after paring down the hyperkeratosis, the classic feature emerges: multiple black dots (thrombosed capillaries) arranged in a linear or scattered pattern. Red punctate vessels may be seen at the periphery. Fissures are very common due to the pressure and shear forces.

C. Flat Warts (Verruca plana):

These are smaller, smoother, and often numerous, appearing on the face, neck, or hands. Their dermoscopic features are more subtle. The surface is only slightly elevated and lacks the coarse papillations of common warts. Vascular patterns are faint; one might see only a few, barely visible red dots or short, linear vessels. The color is often a uniform light brown or skin-colored, sometimes with a faint yellowish tinge. The diagnosis often relies more on the clinical context of multiple, flat-topped papules and the absence of features seen in mimics like seborrheic keratoses.

IV. Dermoscopic Mimics: What Else Could It Be?

The true test of dermoscopic proficiency is not just recognizing a wart, but confidently distinguishing it from its look-alikes. Several common conditions can mimic warts dermoscopically, and a careful comparison is crucial.

A. Seborrheic Keratoses

This is one of the most frequent mimics. Early, non-pigmented seborrheic keratoses can look remarkably like warts. Key differentiating dermoscopic features of early seborrheic keratosis dermoscopy include:
- Comedo-like openings (pseudocomedones): Round, yellowish or brownish, sharply demarcated pits or cysts, which are absent in warts.
- Milia-like cysts: White or yellowish, round, opaque globules scattered throughout the lesion.
- Fissures and ridges (brain-like or cerebriform pattern): While warts have fissures, seborrheic keratoses often show a more organized network of fissures separating flat-topped, island-like structures.
- Hairpin vessels: More common and prominent in seborrheic keratoses than in warts.
The absence of clustered red dots and thrombosed black dots, combined with the presence of milia-like cysts and comedo-like openings, strongly favors a seborrheic keratosis.

B. Corns and Calluses

These are areas of reactive hyperkeratosis without a viral cause. Dermoscopy of a corn reveals a dense, central, translucent, or yellowish core of compact keratin, often with a surrounding erythematous halo. Crucially, they lack the vascular patterns (red dots) and thrombosed capillaries (black dots) that are hallmark features of plantar warts. The surface is more homogenous and lacks the papillary projections.

C. Squamous Cell Carcinoma in situ (Bowen's disease)

This is a more serious mimic that must not be missed. It can present as a scaly, slowly enlarging plaque. Dermoscopy reveals a very different pattern: glomerular vessels (coiled, grouped red dots resembling renal glomeruli) arranged in clusters or scattered on a background that is often pinkish and scaly. It may also have a superficial, brownish, dotted or globular pigmentation. The chaotic, glomerular vascular pattern is distinct from the more orderly punctate or globular vessels of a wart.

V. Practical Tips for Dermoscopy of Warts

To maximize the diagnostic yield of dermoscopy for warts, attention to technique is paramount.

A. Using polarized vs. non-polarized dermoscopy

Most modern dermoscopes offer both modes. Non-polarized dermoscopy (often requiring contact with the skin and a fluid interface) provides excellent visualization of surface features like hyperkeratosis, scales, and fissures. Polarized dermoscopy (which can be contact or non-contact) penetrates deeper and is superior for visualizing vascular patterns (red dots, globules) without the need for fluid. For warts, starting with polarized light to assess the vascular pattern and black dots, then switching to non-polarized to evaluate surface architecture, can provide a comprehensive view. Digital dermoscopy systems often allow easy switching between these modes and are invaluable for capturing both aspects in high resolution for records or teledermatology consultations.

B. Importance of good lighting and magnification

Consistent, bright, white light is essential to avoid color distortion. A magnification of at least 10x is standard, allowing clear visualization of the tiny red and black dots. For plantar warts, gently paring down the thick overlying callus with a scalpel is often necessary to reveal the diagnostic black dots and vessels that lie beneath; attempting dermoscopy without this step can lead to a false-negative assessment.

C. Systematic approach to evaluation

Develop a mental checklist. First, assess the overall pattern and colors (yellowish, scaly). Then, meticulously scan for vascular patterns: look for the characteristic red punctate dots. Next, search for the pathognomonic black dots of thrombosed capillaries. Finally, evaluate the surface for papillations and fissures. Always correlate the dermoscopic findings with the clinical context—the patient's age, the lesion's location, duration, and symptoms. This systematic integration of dermoscopic and clinical data is the essence of accurate diagnosis.

VI. Conclusion

Dermoscopy has firmly established itself as an indispensable adjunct in the diagnosis of common skin lesions like warts. By revealing subsurface vascular patterns and architectural details, it significantly enhances diagnostic accuracy, reducing the rate of misdiagnosis between warts and their common mimics such as corns or early seborrheic keratoses. The key to its effective use lies in recognizing the core dermoscopic triad: the papillary surface dotted with red punctate vessels, the presence of thrombosed black capillaries, and the yellowish hyperkeratotic background. However, it is vital to remember that dermoscopy is a powerful tool, not a standalone test. Its findings must always be integrated with the full clinical picture. A lesion with atypical features, rapid growth, or bleeding should prompt a biopsy regardless of dermoscopic appearance. When used judiciously as part of a comprehensive clinical assessment, dermoscopy empowers clinicians to diagnose warts with greater confidence, leading to more appropriate and timely management for patients.

Warts Dermoscopy Skin Lesions

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