Diagnosing And Treating A Pigmented Lesion On The Hallux

Naohiro Shibuya, DPM, MS, FACFAS

   Verruca. There are many instances in which clinicians may misdiagnose a malignant lesion as verruca. A high index of suspicion is necessary when a verruca lesion appears to be atypical or does not respond to typical treatments.

   Melanoma. The patient went to surgery for an excisional biopsy. Since we were suspicious of melanoma, we decided to obtain a full-thickness specimen with at least 1 mm border around the lesion. Due to the location of the lesion, we anticipated that a circular open wound of approximately 5 mm in diameter would not close primarily without tension. Therefore, a complex skin closure was necessary. Since elliptical incisions with wedge resection would create tension in this tight area, we performed a double S-plasty.

   The specimen came back as a “benign vascular lesion, consistent with cavernous hemangioma.” There was no evidence of malignancy or a melanocytic lesion.

A Closer Look At Melanoma In The Foot

According to the U.S. Central Cancer Registry, the incidence of invasive melanoma in the United States is 59,695 per year.1 Of those, only 0.02 percent happen in the foot.1 Other population studies agree that the incidence and prevalence of melanoma in feet are very small.2-5 However, some smaller studies, conducted in a population with majority of the people having pigmented skin, show a much higher proportion of melanoma in the foot.6-8 It is therefore important to have a higher index of suspicion when a patient has darker skin tone.

   While typical risk factors for melanoma for rest of the body include sun/UV exposure and light skin, these are not risk factors for foot melanoma. Rather, pigmented skin and a history of foot trauma are the major risk factors for foot melanoma. It has been documented that people with a history of puncture wounds to the foot are five to 40 times as likely to develop foot melanoma in comparison to those without a history of trauma.9 Besides these risk factors, a family history of melanoma and a high nevus count are associated with development of foot melanoma. Unlike the rest of the body, the acral lentiginous type of melanoma is more common in the foot than the superficial spreading type.

Key Insights On Prevention And Treatment

Physicians often use the ABCD screening tool to screen melanoma in the rest of the body. Asymmetry, irregular Border, Color and Diameter of more than 6 mm are good indicators for melanoma. The “E” criteria, which stands for “Evolving over time,” has been added in recent years to improve the specificity of diagnosis.10 Having more than one of these five criteria provides up to 97 percent sensitivity while having all five criteria indicates almost 100 percent specificity for melanoma.10 While these criteria are not foot and ankle specific, they are useful for patients to self-screen.

   Screening recommendations of melanoma, however, are not consistent among different organizations. The American Academy of Dermatology recommends frequent self-screening and once a year professional screening.11 The Institute of Medicine simply recommends to “be alert” without any specific guideline.12 On the other hand, the United States Preventive Services Task Force states that there is no evidence to support the need for periodic checkups.13

   Some of the screening guidelines are based on few randomized clinical trials comparing populations with or without periodic melanoma screening. Though the results showed that more melanomas were detected in those who were routinely screened, there was no difference in survival or mortality between the groups.14 Therefore, the need for routine screening was under question.

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