Flat Warts
Verruca plana, or flat warts, are virally induced papules caused by the human papillomavirus (HPV) that can mimic a closed comedone or an acneiform papule. This chapter will discuss the etiology, risk factors, diagnosis, and treatment of flat warts. Table
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Flat Warts Ted Rosen and Sara Risner-Rumohr
11.1
Introduction
Verruca plana, or flat warts, are virally induced papules caused by the human papillomavirus (HPV) that can mimic a closed comedone or an acneiform papule. This chapter will discuss the etiology, risk factors, diagnosis, and treatment of flat warts. Table 11.1 summarizes the similarities and differences between flat warts and acne.
11.2
Background
HPV includes greater than 100 genotypes of a double-stranded DNA virus [1]. Cutaneous HPV types comprise a group of viruses that infect the skin and induce common warts, palmar and plantar warts, flat warts, and butcher’s warts. Classification of warts is based upon morphology, anatomic localization, and HPV typing. Common warts are hyperkeratotic, exophytic papules, or nodules typically associated with HPV-1, HPV-2, or HPV-4 [2]. They are most commonly located on fingers, the dorsal surfaces of hands, and other sites prone to trauma. They typically spare the face but can occur at any anatomical location. HPV types 2, 27, and 57 caused the majority of palmoplantar warts [2]. Myrmecia are large, deep burrowing warts on the plantar surface caused by HPV-1. Most commonly, flat warts that have been analyzed by polymerase chain reaction (PCR) studies contain HPV-3 and, less often, types 10, 28, 29, and 41 [2–6].
T. Rosen, M.D. (*) • S. Risner-Rumohr, M.D. Department of Dermatology, Baylor College of Medicine, 1977 Butler Blvd, Suite E6.200, Houston, TX 77030, USA e-mail: [email protected]; [email protected] J.A. Zeichner (ed.), Acneiform Eruptions in Dermatology: A Differential Diagnosis, DOI 10.1007/978-1-4614-8344-1_11, © Springer Science+Business Media New York 2014
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Table 11.1 Similarities and differences between acne and flat warts Features Flat warts Acne Affected age group—childhood and young adult Yes Yes Koebner phenomenon Yes Occasionallya Follicular-based papules No Yes Flat-topped papules Yes No Virally induced Yes No Ultraviolet light influenced Yes—worsened Yes—most often improved Can heal with a scar Occasionallyb Yes Hormonally influenced No Yes Cellular immunity related Yes No Spontaneously resolve Yes Yes Response to retinoid therapy Yes Yes a Acne can be triggered by minor trauma/friction (e.g., acne mechanica) b Treatments can lead to permanent scarring
The papillomavirus species-specific life cycle is completed only in fully differentiated human squamous epithelia. The infection and induction of hyperproliferation are initiated when the virus enters the basal layer [2]. Unlike other viruses, such as herpes simplex or molluscum contagiosum, HPV does not encode the enzymes required for the replication of viral DNA. HPV is dependent on the host’s cellular machinery for replication. HPV proteins can amplify cell replication acting as viral oncoproteins. However, unlike the high-risk HPV infections located on mucosal surfaces, flat warts have not been linked to dysplasia and cancer [4]. Nongenital warts occur in 7–10 % of the general population,
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