DermaDiagnosis

Can’t Quite Put My Finger On It …

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Can’t Quite Put My Finger On It … image

For at least 10 years, a now 70-year-old man has had a lesion on his left third finger. It is asymptomatic but gradually growing larger. Various primary care providers have offered diagnoses, the most recent being “fungal infection,” but treatments including nystatin cream have had no good effect.

The oval, pink, scaly lesion is located on the medial aspect of the proximal phalanx of the patient’s left hand; it measures 2.3 cm with well-defined borders. It is barely palpable and is not at all tender. No nodes can be felt in the arm or axilla.

The patient is otherwise healthy and is not immunosuppressed. His skin elsewhere shows evidence of sun damage—including actinic keratosis, solar lentigines, and telangiectasias—and removal of several basal cell carcinomas from his face and arms. His elbows, knees, scalp, and nails are free of any notable skin changes.

The most logical next step is to

Treat with oral terbinafine

Treat with topical steroid cream

Perform a shave biopsy

Treat with cryotherapy

ANSWER

The correct answer is perform a shave biopsy (choice “c”). It is a bedrock principle in dermatology that there is no substitute for a correct diagnosis, because correct diagnosis dictates proper treatment. When practical, biopsy is an excellent way to establish the true nature of a lesion and rule out other possibilities; it cuts through all conjecture.

DISCUSSION

The report showed intraepidermal squamous cell carcinoma, also known as Bowen disease. In this case, overexposure to the sun was the probable cause; however, Bowen disease can also develop from non–UV-related triggers, including human papillomavirus, arsenic (usually in contaminated ground water), and radiation treatment.

The differential includes psoriasis (which waxes and wanes), fungal infection (unlikely to last 10 years with so little growth), and superficial basal cell carcinoma.

Treatment success can be achieved by electrodessication and curettage or by the application of 5-fluorouracil or imiquimod cream for a month or two. Rarely, Bowen lesions can become invasive and metastasize if left untreated.

This patient’s prognosis, however, is excellent—at least, as far as this lesion is concerned. His history of sun exposure and numerous skin cancers means he still needs regular visits to dermatology.

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