CASE #2: Keratoacanthoma

Keratoacanthoma (KA) is an epidermal tumor believed to arise from hair follicles and pilosebaceous units. There is an ongoing controversy as to whether KA should be classified as a benign or a malignant tumor. One school of thought considers this tumor to be a clinical variant of well-differentiated squamous cell carcinoma (SCC) because its histopathology and clinical features are similar.5 Another considers KA a separate and benign tumor, given that most lesions undergo rapid growth and spontaneous regression. The incidence of KA increases with age and peaks between ages 50 and 69 years. The condition is twice as common in men as in women. KA has a predilection for fair-skinned individuals and most often presents on sun-exposed skin. The etiology of this tumor remains unknown, although UV light is a major risk factor in the development of KA. Other known risk factors include exposure to chemical carcinogens (particularly pitch and tar), mineral oil, and cigarette smoking. Human papilloma virus types 9, 16, 25, and 37 have been detected in KA lesions, but its role in pathogenesis of KA remains unclear.6 Like PG, KA may develop following skin trauma or surgical incisions. There have been a few reported cases of KA developing at the site of tattoos.

An initial KA lesion presents as a hyperkeratotic papule or nodule. As the lesion matures, it may appear as a dome-shaped reddish-brown or flesh-colored nodule with a shiny and translucent appearance and keratinized central plug. The keratinized plug may emerge like a cutaneous horn. KA occurs on such sun-exposed areas as the nose, eyelids, ears, cheek, neck, and dorsa of hands. KA-like lesions may occasionally occur on such nonhairy areas as the oral cavity, conjunctiva, and subungual region. A rapid growth—achieving a size of 25 mm within six weeks—followed by slow, spontaneous involution in two to six months leaving behind an atrophic scar, is characteristic of most lesions. Unlike PG, KA is rarely tender.

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Pathology reveals well-differentiated squamous epithelium with a mild degree of pleomorphism, atypical keratinocytes, and a central crater filled with keratin. KA may also demonstrate elastic tissue trapping, microabscesses, and eosinophilic infiltration.5 Occasionally, some KA lesions behave atypically, becoming aggressive by invading perineural and perivascular sites as well as regional lymph nodes.7 This is commonly seen in lesions involving the head and neck. There is some question as to whether these cases were actually keratoacanthomas or keratoacanthoma-like SCCs.

Although most KAs are solitary, some individuals may develop multiple lesions. There are a few reported cases of an atypical variant of KA known as keratoacanthoma centrifugum marginatum, which is characterized by multiple small lesions with continuous centrifugal spread, central scarring, and lack of spontaneous remission.8 Other cases featuring multiple lesions are associated with such rare underlying conditions as familial Ferguson-Smith syndrome, Muir-Torre syndrome, and Grzybowski syndrome.5 KA has also been seen in association with such conditions as xeroderma pigmentosum, stasis dermatitis, psoriasis, and discoid lupus erythematosus, as well as in solid-organ transplant patients.

Biopsy and histology is the standard for diagnosis of KA. A well-performed excisional biopsy that preserves the entire lesion, including the center, both sides, and the subcutaneous fat, is recommended.7 The main differential diagnosis is SCC, which can be ruled out with a thorough history and detailed histologic analysis. Unlike KA, SCC usually presents with ulceration, numerous atypical cells, and marked mitosis. Other differential diagnoses to consider include hypertrophic actinic keratoses, verrucous carcinomas, and molluscum contagiosum.

Mohs micrographic surgery is the treatment of choice for KA. Small, solitary KA lesions are occasionally treated with cryosurgery or curettage. However, excisional surgery is strongly recommended, given the potential for misdiagnosis. In patients with multiple KA tumors, intralesional, topical, or oral treatments may be used. Successful therapies include topical 5-fluorouracil, imiquimod creams, oral isotretinoin, intralesional methotrexate, and interferon alpha-2a. Close follow-up is recommended to detect recurrence and confirm diagnosis of KA. The lesion in this case, which showed no sign of involution, was removed with a simple surgical excision without complication.

Dr. Adegbenro is a family medicine resident at the Riverside Regional Medical Center in Newport News, Va. Dr. Scheinfeld is assistant clinical professor of dermatology at Columbia University in New York City, where he has a private practice. Neither has any relationship to disclose relating to the content of thisarticle.


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All electronic documents accessed July 15, 2010.