A 16-year-old girl presents with multiple flat lesions on her forehead (Figure 138-1). 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.
Flat warts on a patient's forehead. (Reproduced with permission from Richard P. Usatine, MD.)
Flat warts are one of the three cutaneous manifestations of warts caused by human papillomavirus (HPV). Flat warts are characterized as flat or slightly elevated flesh-colored papules. Ranging from a few to hundreds of lesions, these warts occur most commonly on the face, hands, and shins and can cause significant patient distress (Figure 138-2).
Flat warts just above the knee of a young woman. Probably spread by shaving. (Reproduced with permission from Richard P. Usatine, MD.)
Plane warts, verruca plana, verruca plana juvenilis.
Flat warts (verruca plana) are most commonly found in children and young adults (Figures 138-1, 138-2, 138-3, 138-4, 138-5).
Flat warts are the least common variety of wart but are generally numerous on an individual.1 They represent up to 4% of all cutaneous warts, while common and plantar warts represent 71% and 34%, respectively.2
Flat warts are usually caused by HPV types 3, 10, 28, and 29.3
Flat warts on the neck of an HIV-positive man. The warts have been spread by shaving. Cryotherapy and imiquimod were not successful, but intralesional Candida antigen injections cleared all the warts. (Reproduced with permission from Richard P. Usatine, MD.)
Flat warts and the common warts on the arm of a young boy. Note how the flat warts are truly flatter and follow a linear pattern due to Koebnerization. (Reproduced with permission from Richard P. Usatine, MD.)
Flat warts around the mouth and cheeks of a 5-year-old boy. (Reproduced with permission from Richard P. Usatine, MD.)
ETIOLOGY AND PATHOPHYSIOLOGY
Like all warts, flat warts are caused by HPV.3 Infection with HPV can occur by coming in direct contact with intact, macerated, or traumatized skin.
Flat warts may spread in a linear pattern secondary to spread by scratching or trauma, such as shaving (Koebner phenomenon) (...