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Patient Story
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A 16-year-old girl presents with multiple flat lesions on her forehead (Figure 117-1). It started with just a few lesions but has spread over the past 3 months. She is diagnosed with flat warts and topical imiquimod is prescribed as the initial treatment.

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FIGURE 117-1

Flat warts on a patient’s forehead. (Used with permission from Richard P. Usatine, MD.)

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Introduction
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Flat warts are characterized as flat or slightly elevated flesh-colored papules. They may be smooth or slightly hyperkeratotic. They range in size from 1 to 5 mm or more, and numbers range from a few to hundreds of lesions, which may become grouped or confluent. They occur most commonly on the face, hands, and shins. They may appear in a linear distribution as a result of scratching, shaving, or trauma (Koebner phenomenon) (Figures 117-2 and 117-3).

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FIGURE 117-2

Flat warts just above the knee of a young woman. Notice the linear distribution probably resulting from spread by shaving (Koebner phenomenon). (Used with permission from Richard P. Usatine, MD.)

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FIGURE 117-3

Flat warts on the hand of a child. Note the linear distribution, which is probably the result of scratching or minor trauma (Koebner phenomenon). (Used with permission from Richard P. Usatine, MD.)

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Synonyms
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Plane warts, verruca plana, verruca plana juvenilis, plane warts.

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Epidemiology
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  • Flat warts (verruca plana) are most commonly found in children and young adults (Figures 117-1 to 117-3).

  • Flat warts are the least common variety of wart, but are generally numerous on an individual.1

  • Flat warts are usually caused by human papillomavirus (HPV) types 3, 10, 28, and 29.2

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Etiology and Pathophysiology
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  • Like all warts, flat warts are caused by HPV.2

  • Flat warts may spread in a linear pattern secondary to spread by scratching or trauma, such as shaving (Figure 117-2 and 117-3).

  • Flat warts present a special treatment problem because they persist for a long time, they are generally located in cosmetically important areas, and they are resistant to therapy.

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Risk Factors
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  • Shaving next to infected areas (Figures 117-2 and 117-3).

  • HIV infection or other types of immunosuppression.

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Diagnosis
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Clinical Features
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  • Multiple small, flat-topped papules that may be pink, light brown, or light yellow colored. They may be polygonal in shape (Figure 117-4).

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FIGURE 117-4

Close-up of a flat wart. Note typical small, flat-topped ...

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