INTRODUCTION

Warts are viral infections caused by the human papillomavirus (HPV), which may affect both the skin and mucous membranes. They are one of the most common dermatological conditions, frequently prompting patients to seek medical attention. The causative agent, HPV, has over 200 subtypes, with some types being associated with different clinical manifestations of warts [1]. These manifestations are generally classified into four main forms: common, flat, palmoplantar, and corneiform warts. Each type has distinct morphological features influenced by factors such as the patient’s immune status, the site of infection, and the specific HPV subtype involved [2,3].

The variable clinical presentation of cutaneous warts may pose a significant diagnostic challenge. Warts may mimic other dermatologic conditions, including seborrheic keratosis, molluscum pendulum, molluscum contagiosum, and even more serious lesions such as squamous cell carcinoma. This overlap in clinical features makes it essential for clinicians to rely on additional diagnostic tools to arrive at an accurate diagnosis. One such valuable tool is dermoscopy, a non-invasive imaging technique that is able to distinguish cutaneous warts from other diagnoses. The aim of this work was to determine the effectiveness of dermoscopy in the positive diagnosis of cutaneous warts and differentiating them from lesions that may have a similar clinical presentation. Additional mimics were added based on a literature review.

MATERIALS AND METHODS

This was a prospective study conducted over an eighteen-month period from January 2023 to June 2024 at a department of dermatology.

Clinical and dermoscopic images of cutaneous warts from different parts of the body (except the genital area) and clinically wart-like lesions were collected. Mimics were divided according to the clinical form and location of the warts. Patients included in this study were subjects of all ages. For each patient, clinical information was recorded, including age and the anatomical location of the lesion. Images were taken before the beginning of any treatment to ensure accurate documentation of the natural appearance of the lesion. Dermoscopic examination was performed using the DermLite DL4 dermoscope. The dermoscopic features of each lesion were analyzed by two dermatologists to identify features associated with cutaneous warts and distinguish them from potential mimics.

RESULTS

We collected 70 cutaneous warts in a total of 50 patients (15 men, 13 women, 22 children). There were 35 (50%) common warts, 23 (32.8%) palmoplantar warts, 10 (14.3%) flat warts, and 2 (2.9%) corneiform warts. The age of the patients ranged from 3 years to 65 years. Flat warts were more common in children, with an average age of 5 years, while the highest average age was that of common warts, with an average of 45 years. We also collected 40 lesions clinically mimicking cutaneous warts according to the locations, including different diagnoses: molluscum contagiosum (n = 10, 25%), calluses (n = 6), seborrheic keratosis (n = 6, 14%), molluscum pendulum (n = 5, 12.5%), histiocytofibroma (n = 4, 10%), cutaneous corn (n = 3, 7.5%), squamous cell carcinoma (n = 2, 5%), Bowen’s disease (n = 1, 2.5%), lichen planus (n = 1, 2.5%), psoriasis (n = 1, 2.5%), and exostosis (n = 1, 2.5%).

Common warts: Thirty-five cutaneous warts were diagnosed as common warts. They were subdivided into four groups according to clinical presentation and location: dome-shaped warts (n = 17), periungual warts (n = 11), filiform warts (n = 5), and hyperkeratotic warts (n = 2).

Dome-shaped warts presented as slightly keratotic papules and plaques, mainly located on the limbs (n = 15), and more rarely on the face (n = 2). The main common dermoscopic features found were: dotted vessels surrounded by a whitish halo creating a frog’s egg appearance, hemorrhagic pitting, a yellowish papillomatous surface and superficial scales. Two lesions also had linear vessels. Given this clinical presentation, histiocytofibroma, squamous cell carcinoma, and irritated seborrheic keratosis were the various imitators collected; dermoscopy helped to correct the diagnoses (Table 1).

Table 1: Different clinical and dermoscopic forms of the cutaneous warts and their mimickers.

Periungual warts presented as keratotic papules and plaques, mainly located under the nail (n = 8) at the level of the lateral folds and the proximal fold (n = 3). Dermoscopy showed a frog’s egg appearance, dotted vessels, and scales. Five lesions had a papillomatous surface. Nail Bowen’s disease and exostosis were the imitators found (Table 1).

Hyperkeratotic warts presented as hyperkeratotic plaques, located at pressure zones (knees). Dermoscopy showed thick scales with the presence of some hemorrhagic spots. A case of psoriasis localized at the knees and calluses on the knee was the imitator found (Table 1).

Filiform warts presented in the form of papules or plaques with filiform projections located on the face (n = 3) and the scalp (n = 2). Dermoscopy showed filiform projections with linear vascularization surrounded by a whitish halo. This form presented a differential diagnosis with molluscum pendulum (Table 1).

Palmoplantar warts presented in the form of keratotic plaques located in the plantar (n = 15) and palmar (n = 8) areas. Dermoscopy showed a frog’s egg appearance, hemorrhagic spots, scales, and an interruption of the dermatoglyphs. Five lesions had a yellowish papillomatous surface. This location presented a differential diagnosis with calluses (Table 1).

Flat warts presented as flat papules located on the face (n = 5) and limbs (n = 5). Dermoscopy showed vessels in points on a red (n = 5), pale (n = 3), and brown (n = 2) background. Lichen planus, molluscum contagiosum, and seborrheic keratosis were the imitators found (Table 1).

Corneiform warts presented as keratotic papules located on the face (n = 1) and neck (n = 1). Dermoscopy showed linear and hairpin vessels surrounded by a whitish halo. This form clinically mimics cutaneous corns and presents clinical and dermoscopic similarities with squamous cell carcinoma (Table 1). The results found are summarized in Table 1 and presented in Figures 1 – 5.

	Figure 1: (a) 15-year-old patient with a dome-shaped papule with a slightly scaly surface on the forearm. (b) 20-year-old patient with a dome-shaped erythematous papule on the forearm. (c) Dermoscopy showing dotted vessels surrounded by a whitish halo creating a frog’s egg appearance and papillomatous surface suggesting a common wart. (d) Dermoscopy showing a peripheral whitish network with a central amorphous zone suggesting an histiocytofibroma.
	Figure 2: (a) 15-year-old patient with an erythematous filiform papule on the nose. (b) 30-year-old female patient with a filiform pigmented papule on the free edge of the lower eyelid. (c) Dermoscopy showing filiform projections with linear vessels surrounded by a whitish halo suggesting a filiform wart. (d) Dermoscopy showing filiform projections without vascularization related to the molluscum pendulum.
	Figure 3: (a) 50-year-old patient with subungual hyperkeratosis evolving for six months. (b) 45-year-old patient with distal onycholysis with subungual hyperkeratosis evolving for one year. (c) Dermoscopy showing a papillomatous surface, a frog’s egg appearance, and hemorrhagic pitting suggesting a wart. (d) Dermoscopy showing distal onycholysis, subungual hyperkeratosis, and multiple glomerular vessels in favor of Bowen disease confirmed histologically.
	Figure 4: (a) 10-year-old child with flat papules on the back of the hands and forearms. (b) 10-year-old child with flat, millimetric, slightly keratotic papules on the two upper limbs. (c) Dermoscopy showing pointed vessels on a red background, suggesting a flat wart. (d) Dermoscopy showing Wickham’s streaks, dotted vessels, and an erythematous background suggesting lichen planus confirmed histologically.
	Figure 5: (a) 30-year-old patient with a plantar keratotic plaque. (b) 40-year-old patient with a plantar hyperkeratotic plaque. (c) Dermoscopy showing hemorrhagic spots and the interruption of the plantar lines in favor of plantar wart. (d) Dermoscopy showing a central nucleus, the absence of vascularization, and the persistence of the plantar lines in favor of a callus.

DISCUSSION

The clinical and dermoscopic features of cutaneous warts differ depending on the shape and location.

Common warts may appear clinically in different forms: dome-shaped, hypertrophic, periungual, and filiform. Common warts are mainly characterized by the presence of dotted vessels surrounded by a whitish halo creating a frog’s egg appearance. This is associated with the presence of hemorrhagic pitting related to thrombosis of the dermal vessels and a papillomatous surface. Filiform projections and linear vascularization surrounded by a whitish halo are found in filiform warts. Our results were similar to those in the literature [4,5].

In addition to the mimics found in our study, other lesions that may appear as common warts are reported in the literature [6–10].

Adult xanthogranuloma, a form of non-Langerhans cell histiocytosis, presents as a yellow to reddish, dome-shaped papule or nodule. This clinical presentation may mimic dome-shaped warts. However, dermoscopy shows a sunset profile that helps establish the diagnosis [6].

Squamous cell carcinoma of the nail may present clinically as a wart. Dermoscopy shows hairpin vascularization, polymorphic vessels, onycholysis, and a verrucous surface [7]. In our series, we found one case of subungual Bowen’s disease whose diagnosis was suspected by dermoscopy and confirmed by histology.

Flat warts appear clinically as smooth-surfaced papules, often multiple, that occur primarily on the face and back of the hands. Dermoscopy shows vascularization; mainly dotted vessels, on a red, light brown, or pale background [4,5].

Our study found the following imitators of flat warts: seborrheic keratosis, lichen planus, and molluscum contagiosum.

Kim et al. published a comparative study between seborrheic keratosis type flat warts and flat warts. They suggested a diagnostic algorithm using the Koebner phenomenon, dermoscopic findings, distribution of each lesion and a biopsy for multiple lesions in adults [8].

Gurioli reported the case of a 29-year-old patient who presented with keratotic papules on the back of the hands mimicking cutaneous warts that had been evolving for four years. Dermoscopy showed linear and irregular dotted vessels on a pink to whitish background, given the resistance to conventional treatments and the chronic evolution, a biopsy was done confirming the diagnosis of granuloma annulare [9].

Palmoplantar warts present clinically as single or multiple keratotic papules. Dermoscopy shows a frog’s egg appearance, hemorrhagic pitting, and the interruption of the palmoplantar lines [4,5]. In our series, the clinical presentation mainly mimicked calluses, yet dermoscopy helped to correct the diagnosis. Other mimickers have been reported in the literature [11–14]. Lee et al. reported four patients who underwent hematopoietic stem cell transplantation and presented with keratotic papules at the palmoplantar level mimicking cutaneous warts. Histology confirmed the diagnosis of chronic lichenoid graft-versus-host disease [11]. Diani et al. reported a case of acquired lymphangioma of the hallux initially treated as a wart, yet a biopsy allowed the diagnosis to be made [12].

The corneiform wart is an entity rarely reported in the literature. Dermoscopy mainly finds linear and hairpin vessels surrounded by a whitish halo, posing a diagnostic challenge with corneiform squamous cell carcinoma [15], hence the importance of histological confirmation in doubtful cases, especially if it appears late in life.

CONCLUSION

The variability of clinical presentations of cutaneous warts, as observed in our study, underlines the need to use dermoscopy to improve diagnostic accuracy and help distinguish them from their imitators. Indeed, dermoscopic analysis revealed characteristic patterns, including a frog-egg appearance, a yellowish papillomatous surface, and hemorrhagic pitting, which allowed the diagnosis to be made in the majority of cases. However, when doubt persists, histological confirmation remains essential to ensure an accurate diagnosis and appropriate management. This approach minimizes diagnostic errors and avoids unnecessary interventions.

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