Diagnosis: Flat warts

Our patient had flat warts, or verruca plana, viral-induced, slightly elevated flat-topped papules, 2-4 mm in diameter, with minimal scale. The warts tend to be flesh-colored or slightly pigmented. Flat warts are most commonly found on the face, hands, and lower legs. Linear grouping of lesions at sites of skin trauma is not uncommon. Trauma to the skin greatly aids in the inoculation and spread of warts.

The human papillomavirus (HPV) includes >90 genotypes that infect human epithelial cells. Most flat warts that have been analyzed by polymerase chain reaction (PCR) studies contain HPV type 3 or 10. Although some forms of HPV infection have been linked to dysplasia and cancer, especially when located on mucosal surfaces, such as the cervix, larynx, and rectum, this is not the case with flat warts.

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Even in the absence of visible warts, one of the HPV types is almost universally found on the skin surface.1 If a wart is present, two or more HPV types are detected by PCR testing.2 This begins to explain the observation of HPV lesions in 88 virgins at the outpatient office of one medical school3 and the detection of genital HPV carriage in prepubertal girls without sexual exposure.4 Thus, detection of HPV in the cervical tissues of a female does not indicate that treatment is needed.1

Considerations for treatment include the patient’s age, immune status, skin integrity, and cosmesis. It is important to remember that warts have their individual spectrum of survival strategies. These include hiding from the immune detection apparatus within the epidermis. Any irritation or inflammation of the skin might secondarily precipitate an immunologic response against the invading virus. 

As for OTC products, keratolytics with salicylic acid are available in the form of solution and pads. These cause chemical debridement of the wart’s keratotic surface and minimal reduction of lesion size (they also cause a white discoloration). Products containing dimethyl ether and propane (e.g., Dr. Scholl’s Freeze Away and Compound W Freeze Off) are available, but they have had limited success clinically. 

Topical cantharidin produces local epidermal necrosis. Responses can vary, and some individuals experience scarring. Podophyllin is another topical modality; however, it tends to be beneficial only for mucosal lesions. Cryotherapy using liquid nitrogen is ablative and, for many patients, offers a good balance of efficacy and side effects. Contact immunology is an effective nonablative modality for warts, but it is greatly limited because the preferred stimulants, dinitrochlorobenzene and diphenylcyclopropenone, have not been approved by the FDA. Imiquimod is a topical immune response modifier approved for warts on mucosal surfaces and probably has little value for warts on thick skin surfaces. Ablation of warts with direct surgery, electrodesiccation, or lasers is effective but has the potential disadvantage of scar formation. Also, wart recurrence in or around the site of treatment is possible because virologic cure of patients is not always achieved by simple removal.

Our patient’s warts were successfully eliminated with two sessions of cryotherapy administered three weeks apart.

Dr. Burkhart is clinical professor of dermatology at Medical University of Ohio at Toledo and clinical assistant professor of dermatology at Ohio University, College of Osteopathic Medicine, in Athens.

1. Burkhart CG. The endogenous, exogenous, and latent infections with human papillomavirus. Int J Dermatol. 2004;43:548-549.
2. Harwood CA, Spink PJ, Surentheran T, et al. Degenerate and nested PCR: a highly sensitive and specific method for detection of human papillomavirus infection in cutaneous warts. J Clin Microbiol. 1999;37:3545-3555.
3. Frega A, Cenci M, Stentella P, et al. Human papillomavirus in virgins and behaviour at risk. Cancer Lett. 2003;194:21-24.
4. Powell J, Strauss S, Gray J, Wojnarowska F. Genital carriage of human papilloma virus (HPV) DNA in prepubertal girls with and without vulval disease. Pediatr Dermatol. 2003;20:191-194.