CASE #2: Myrmecia

Our patient had deep-seated warts, also known as myrmecia. The warts, which are caused by the type 1 human papillomavirus (HPV), manifest as delled (centrally depressed) hyperkeratotic lesions thought by some to resemble an anthill. (Bulldog ants belonging to the species <em>Myrmecia</em> and endemic to Australia inhabit delled mounds, lending their name to the disorder.) On histology, myrmecia can have an endophytic epidermal growth pattern and possess virion-loaded basophilic nuclear inclusions and basophilic parakeratotic cells in the upper epidermis. Abundant polygonal, refractile-appearing eosinophilic inclusions (ring forma- tions of keratin filaments) associated with HPV 1 E4 gene products (a 17-kDa E1-E4 fusion protein and a 16-kDa species lacking the five E1 amino acids and a few E4 residues) are also apparent.

The body areas most commonly affected by warts are the hands and feet. Some studies suggest that HPV types 2, 27, and 57 cause the majority of palmoplantar warts. HPV types 1, 2, 3, 4, 27, 29, and 57 have been noted to be a significant cause of warts elsewhere on the body.

One of the most common skin infections, warts are estimated to occur in at least 10% of the population and account for approximately 10% of visits to physicians by patients seeking dermatologic care. The morbidity associated with warts is not insignificant because of the pain they induce when they occur on the feet and the emotional distress they engender when they occur on the hands, as they are visible to others during hand shaking.

Besides myrmecia, other types of warts occur on the feet. HPV 4, 60, 63, and 65 induce plantar cysts that form inclusion warts of the sole. Any type of plantar wart can coalesce into large plaques termed mosaic warts.

When a patient presents with a verrucous lesion, the most common misdiagnosis for a wart is a callus. Three clinical findings distinguish warts from calluses: (1) Warts commonly possess visible black dots, which represent thrombosed capillaries. Skin cells affected by warts secrete a factor that induces the formation of additional but not necessarily functional blood vessels. Calluses do not exhibit black dots. (2) Warts often break the continuity of the skin lines (dermatoglyphics), while calluses do not. (3) Warts are frequently painful when subjected to direct and lateral pressure, but calluses are often painful only to direct pressure.

The ideal treatment for palmoplantar warts has yet to be devised. Warts can disappear spontaneously. The larger their size and the longer they have been present, the less likely warts are to disappear without treatment. Cyrotherapy and keratolytic topical agents (salicylic acid in the form of poultices or a liquid) are the mainstay of treatment. A 10-second exposure to liquid nitrogen has been found to be more effective, albeit with a higher incidence of side effects, than shorter durations of liquid nitrogen exposure.

Some interesting differences in treatment efficacy between plantar and hand warts have emerged, based on clinical trials and other therapeutic approaches. One open, randomized, parallel-group study found that two freeze-thaw cycles were more effective than cryotherapy at three-week intervals for plantar but not hand warts.1 Paring improves the cure rate for plantar warts but not for hand warts.2 Bleomycin in solution is a useful treatment for recalcitrant warts (I think particularly for plantar warts), but it has a variety of side effects, including possible pain during and after treatment, pigment changes, purple digit, Raynaud phenomenon, necrotic eschar, scarring, and nail damage.3

Dr. Scheinfeld is assistant clinical professor of dermatology at Columbia University in New York City, where he has a private practice.

 

References

1. Berth-Jones J, Bourke J, Eglitis H, et al. Value of a second freeze-thaw cycle in cryotherapy of common warts. Br J Dermatol. 1994;131:883-886.

2. Berth-Jones J, Hutchinson PE. Modern treatment of warts: cure rates at 3 and 6 months. Br J Dermatol. 1992;127:262-265.

3. Hayes ME, O’Keefe EJ. Reduced dose of bleomycin in the treatment of recalcitrant warts. J Am Acad Dermatol. 1986;15(5 Pt 1):1002-1006.