Recognizing Amelanotic Melanoma In The Lower Extremity
Due to the potentially dire consequences of amelanotic melanoma, early diagnosis is critical. Accordingly, this author reviews the challenges of the differential diagnosis, discusses a variety of insightful case studies and offers a protocol for facilitating more timely biopsies of suspicious lesions.
In days gone by in the podiatric literature, the reporting of melanoma of any type on the lower extremity, particularly the feet, was a relatively uncommon occurrence. In my experience, most of these reports in the podiatric literature were “surprise” diagnoses. More accurately, treatment for some lesion would begin and based on non-response to treatment, someone decided to do a biopsy, yielding the true nature of the lesion as melanoma.
I have been studying melanoma since 1982 and have been speaking about it since 1995. I am still surprised to hear podiatric clinicians tell me that after 40 years of practice, they have never seen a melanoma. At this point, it is not a matter of not seeing it. It is a matter of missing it.
In the lay and professional literature, it is well documented that melanoma has been skyrocketing in incidence over the last half century. If we only include invasive melanoma, the incidence of developing melanoma in someone born today and living a normal lifespan in the United States is 1 in 50.1 In 1930, the incidence was 1 in 1,500. If we include both non-invasive and invasive presentations of melanoma, the incidence is currently 1 in 32.
In 2009, there were 121,840 new cases of melanoma in the United States with 68,720 being invasive and 53,120 were in-situ. (Researchers have recently noted an explosive increase in the incidence of non-melanoma skin cancers as well.2) Melanoma in-situ is defined as being confined to its origin in the epidermis. Invasive melanoma is defined as having extended into the dermis, thus gaining access to the blood vessels and lymphatics, and the ability to metastasize. In 2009, 8,650 deaths were recorded as a result of melanoma.1
Simply stated, melanoma is occurring in your patients and it is occurring in your area of expertise. Indeed, DPMs have an obligation to survey patients’ skin in their area of expertise and licensure for suspect lesions.
As far as melanomas go, about 30 to 35 percent of all lesions occur on the lower extremities.3 If physicians diagnose melanoma at the non-invasive or in-situ stage, it is thought to be completely curable if one excises it at this stage. Once melanoma becomes invasive, the five-year survival rates decrease in direct proportion to the thickness (depth in millimeters) of the lesion. The pathology report will also note other parameters such as Clark’s levels, the presence of mitotic figures and whether there is vessel or lymphatic invasion. There is 10 times more incidence of melanoma in Caucasians than African-Americans.4
What You Should Know About Diagnosing Pigmented Lesions
Most students and clinicians are well versed in the diagnostic criteria (the ABCDE mnemonic) for pigmented lesions that should give one a high index of suspicion that the lesion might be a melanoma.
Asymmetry. This is defined as a lesion that one is unable to bisect in any way that produces mirror images.
Border irregularity. This is defined as scalloped edges or poor definition as to where the lesion begins or ends.
Color variegation. In early lesions, this refers to varying shades of tan to brown to black. In later stages, this changes to red, white and blue.
Diameter greater than 6 mm. This refers to the fact that most melanomas do not reveal themselves until they are at least 6 mm in the widest dimension.
However, lesion diameter less than 6 mm alone does not rule out melanoma.
Enlargement or elevation. This can be noted by the clinician or related by the patient. In my mind, this by itself is enough to warrant a biopsy.