CASE #2: Actinic keratosis
AKs are premalignant lesions that, if not treated, have a potential to evolve into SCC. An extremely common condition,5 AKs are an important finding because of their malignant potential and because they are a marker of individuals that are at a higher risk of such nonmelanoma skin cancers as SCC and basal cell carcinoma (BCC).5
AKs represent proliferations of cytologically aberrant epidermal keratinocytes that develop secondary to UV exposure.5 UV radiation-induced mutations in p53, a tumor-suppressor gene, play an important role in the development of AKs and their subsequent progression to SCC. This mutation is present in more than 90% of SCC.5 Risk factors for AK include cumulative exposure to UV radiation and susceptibility factors such as light-colored skin and eyes as well as immunosuppression.5
AKs are typically found on chronically sun-exposed areas of the body and are most common on the upper limbs. There are clinical variants of AKs, but the most common lesion is a 2- to 6-mm erythematous, scaly papule that is usually more easily felt than seen.5 AKs can also be more hyperkeratotic and may produce a cutaneous horn, manifesting as columns of thick cornified material that protrude above the skin.6 These lesions should be biopsied to rule out SCC, although the most common lesion under a cutaneous horn is an AK.5
The experienced practitioner can accurately make the diagnosis of AK through clinical examination alone. The differential diagnosis includes benign lichenoid keratoses, seborrheic keratoses, SCC, SCC in situ, BCC, and porokeratosis.5 Clinically, the most important distinction to make is between an AK and SCC. Findings that are more concerning for SCC include tenderness,6 induration, larger size, ulceration, bleeding, rapid growth, and recurrence after treatment.5 Any lesions that are suspicious for SCC should be biopsied for definitive diagnosis.
Characteristic histologic findings of AK include foci of atypical, pleomorphic keratinocytes in the basal cell layer. Overlying these foci of abnormal cells, there is irregular acanthosis and hyperkeratotic parakeratosis. There is sparing of the adnexal epithelium with orthokeratosis overlying these stuctures. This gives rise to the so-called “flag sign” of alternating ortho- and parakeratosis.5
AKs are most commonly treated with liquid nitrogen cryotherapy. Other options include topical 5-fluorouracil, topical imiquimod, curettage with or without electrodesiccation, and photodynamic therapy.6
This patient was treated with cryotherapy to the larger lesions on his hands, forearms, and ear helices. The smaller lesions over his scalp, forehead, neck, and nose were treated with three weeks of topical 5-fluorouracil. The patient returned for follow-up examination two months later and described significant erythema and crusting, along with a burning sensation that occurred during the second half of treatment with the 5-fluorouracil and slowly improved after completion of therapy. At his next follow-up appointment, the scaly lesions on his arms had resolved along with the majority of the lesions on his head and neck. Two remaining lesions on his scalp were subsequently treated with cryotherapy.
Dr. Doherty is a resident in the department of dermatology at Baylor College of Medicine in Houston. He has no relationships to disclose relating to the content of this article.
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2. James WD, Berger TG, Elston DM. Genodermatoses and congenital anomalies. In: Andrews’ Diseases of the Skin: Clinical Dermatology. 10th ed. Philadelphia, Pa.: Saunders-Elsevier; 2006:566-567.
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4. Wolff-Schreiner EC. Porokeratosis. In: Fitzpatrick’s Dermatology in General Medicine, 6th ed. New York, N.Y.: McGraw Hill; 2003:532-537.
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6. Rigel DS, Cockerell CJ, Carucci J, Wharton J. Actinic keratosis, basal cell carcinoma and squamous carcinoma. In: Bolognia JL, Jorizzo JL, Rapini RP, eds. Dermatology. 2nd ed. Philadelphia, Pa.: Mosby-Elsevier; 2008:1641-1659.