Photo Rounds

Pigmentation on foot

A 72-year-old white woman asked her family physician (FP) to examine her foot, which had been hurting her for 2 months. During his examination, the FP noted a large pigmented area on the bottom of the foot. The patient was unaware of this pigmentation because she had osteoarthritis and her mobility was limited.

What’s your diagnosis?


Pigmentation on foot

The FP suspected that this was an acral lentiginous melanoma (ALM).

The FP considered the various ways to biopsy this lesion. Doing a biopsy of the whole lesion was neither practical, nor desirable, given that the lesion was >2 cm and located on the bottom of the patient’s foot. And while incomplete sampling could result in a false negative result, this lesion was so suspicious for melanoma that any well-performed biopsy would likely produce a diagnosis of melanoma. (Of course if melanoma was not diagnosable with partial sampling, a full excisional biopsy would be needed.)

The FP also debated doing a 6-mm punch biopsy vs a shave biopsy; his intent was to get below some of the deeper pigment. Incisional biopsy done as a small ellipse with suturing was also an option. It would also be the most time consuming.

The FP presented the biopsy options to the patient and explained that the shave biopsy would require a dressing and the punch biopsy would require sutures, which would need to be removed at the next visit. Both biopsy methods would likely cause the foot to be uncomfortable to walk on for several days.

The FP and patient decided to do a deep shave biopsy (saucerization). After administering local anesthesia with lidocaine and epinephrine, the FP performed a deep shave biopsy that included about 1 cm of the darkest and thickest portion of the suspected melanoma.

The biopsy results indicated that the patient had an acral lentiginous melanoma, which measured 0.7 mm at its deepest point in the biopsied portion. The patient was referred to Orthopedics for a wide excision and repair. A sentinel node biopsy was not needed because the lesion was less than 1 mm in depth and there was no ulceration. The surgery and healing time were challenging for the patient, but she did not lose her foot and has remained cancer free.

Photo courtesy of Jonathan Karnes, MD and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Karnes J, Usatine R. Squamous cell carcinoma. In: Usatine R, Smith M, Mayeaux EJ, et al. Color Atlas and Synopsis of Family Medicine. 3rd ed. New York, NY: McGraw-Hill; 2019:1103-1111.

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