A 64-year-old woman presented with an enlarging lesion on the back of her right calf. She initially noted a small, raised, white area 2 to 3 months earlier that progressively enlarged. The lesion was not painful or pruritic. The patient had no other skin lesions or history of trauma to the area. Treatment had not been attempted, including nonprescription medications. She had a history of hypertension.

Physical examination revealed a dome-shaped lesion that was 1 cm in diameter and had central hyperkeratosis (Figure 1).

Question

Based on the patient's history and physical examination, which one of the following is the most likely diagnosis?

• A. Amelanotic melanoma.

• B. Keratoacanthoma.

• C. Nodular basal cell carcinoma.

• D. Prurigo nodularis.

Discussion

The answer is B: keratoacanthoma. This is an unpredictable skin tumor that may behave similarly to a squamous cell carcinoma. Keratoacanthomas typically present as a solitary, rapidly growing nodular lesion, often with central hyperkeratosis, on sun-exposed areas in older adults. The mean age at diagnosis is 64 years. Keratoacanthomas often evolve in the three stages of proliferation, maturation, and spontaneous resolution, typically over 4 to 6 months.¹ Risk factors for development of keratoacanthomas include ultraviolet light exposure and skin trauma.²