A 55‐year‐old white male presented with a lesion on the dorsal aspect of his left forearm where his dog had scratched him 5 to 6 weeks prior. Rapid growth of the lesion had followed, and the area became mildly erythematous. The patient denied any pain, itching, or bleeding. Personal history included smoking and sun exposure; he had no personal or family history of skin cancer. A 2.2‐ × 1.6‐cm, firm, raised, pink plaque with heaped up borders and a central verruciform appearance was noted on the dorsal, left, mid forearm. Scattered, thin, yellow keratotic and hemorrhagic crusts were present on the surface superficially (Figure 1).
>WHAT IS YOUR DIAGNOSIS?
* Basal cell carcinoma
* Irritated seborrheic keratosis
The lesion was a keratoacanthoma (KA), a common skin tumor that can develop as a solitary lesion or less commonly at multiple sites. A rapid growth phase is usually followed by spontaneous involution. A case can be made for rapid growth being almost pathognomonic for KA. In rare cases, metastasis has occurred. A KA may start at the site of a minor injury and often is referred to as a volcanic eruption on the skin.1 Hair‐bearing, sun‐exposed skin is commonly affected on middleaged and elderly fair‐skinned individuals. 2 A history of chronic overexposure to the sun is almost always found. Incidence is difficult to estimate, as many KAs will spontaneously resolve without being reported and those that are documented often have pathology that classifies them as a subtype of squamous cell carcinoma (SCC).2–5 During the growth phase, significant tissue destruction may occur, and involution may take many months. In consideration of these factors and because definitive differentiation from aggressive SCC can be challenging, most KAs are treated rather than observed for spontaneous resolution.5
Differential diagnosis Most basal cell carcinomas manifest as a slowgrowing, raised, pearly papule or nodule with telangiectasias and a central ulceration. Irritated seborrheic keratoses are common benign skin lesions with a stuck‐on appearance that occur on hair‐bearing skin and are sometimes itchy or mildly uncomfortable. A biopsy is often required for definitive diagnosis.
Treatment KAs are commonly managed with excisional or Mohs surgery (reserved for larger lesions and those in anatomically sensitive areas). Smaller solitary or early multiple KAs may respond well to simple curettage with electrodessication.4 Additional treatment options include cryotherapy with liquid nitrogen, radiotherapy, laser surgery, intralesional steroid injections, or topical and intralesional chemotherapy; however, the rate of reoccurrence with these modalities has not been widely studied.4 Topical imiquimod has documented benefits in inducing regression.6 Systemic therapies with retinoids, methotrexate, and 5‐fluorouracil have been used for multiple eruptive KAs.4 Strict sun avoidance is strongly recommended for prevention. JAAPA
1. Pattee SF, Silvis NG. Keratoacanthoma developing in sites of previous trauma: a report of two cases and review of the literature. J Am Acad Dermatol.
2. Karaa A, Khachemoune A. Keratoacanthoma: a tumor in search of a classification. Int J Dermatol.
3. Ko CJ, McNiff JM, Bosenberg M, Choate KA. Keratoacanthoma: clinical and histopathologic features of regression. J Am Acad Dermatol.
4. Schwartz RA. Keratoacanthoma: a clinico-pathologic enigma. Dermatol Surg.
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5. Ko CJ. Keratoacanthoma: facts and controversies. Clin Dermatol.
6. Dendorfer M, Oppel T, Wollenberg A, Prinz JC. Topical treatment with imiquimod may induce regression of facial keratoacanthoma. Eur J Dermatol.