Recognizing Amelanotic Melanoma In The Lower Extremity

Author(s): 
Bryan C. Markinson, DPM, FASPD

   Therefore, for most melanomas, clinicians will be alerted by the fact that the lesion produces melanin and thereby becomes a different color (usually tan to brown to black) to the surrounding skin. This allows for assessment according to the aforementioned established criteria.

Navigating The Potential Pitfalls Of Diagnosing Amelanotic Melanoma

As if this is not difficult enough, there is a variant of melanoma that is deficient in pigment or produces no pigment at all. This is amelanotic melanoma. Specifically because of the lack of pigment, these lesions are commonly diagnosed at later stages and deeper levels, especially on the feet. They are more commonly associated with the nodular subtype of melanoma and represent less than 5 percent of all melanomas. Due to the lack of pigment, we do not have repeatable criteria for diagnosis such as the aforementioned ABCDE mnemonic for pigmented lesions of the skin.

   Theoretically, amelanotic presentations can occur in any type of melanoma. There are case reports of amelanotic acral lentiginous melanoma, amelanotic lentigo maligna melanoma and amelanotic superficial spreading melanoma.5-7 In addition to the difficulty of diagnosing these lesions due to the lack of pigment, other misdiagnoses include eczema, edema, Bowen’s disease and actinic keratoses.6 Physicians have also reported nail bed papulosquamous disease and resulting nail plate dystrophy without pigmentation. This includes nail plate striations, thinning, lysis and splinter hemorrhages.5

   Other nail unit disturbances include nail bed granulation tissue, loss of the nail plate, furrows in the nail plate and drainage. In my experience, chronic paronychia is by far the most common misdiagnosis of subungual amelanotic melanoma, most commonly the nodular type.

   When appearing on skin, amelanotic melanomas typically present as pink, reddish or flesh colored. Due to the lack of the tip-off of pigment, the lesions are commonly not diagnosed until growth occurs and/or the lesions begin to become symptomatic (itching or pain), bleed or are chronically irritated by clothing or footwear.8 For a summary of clinical findings of amelanotic melanoma, see “Key Facts About Amelanotic Melanoma” at right.

   Further complicating the diagnosis of amelanotic melanoma, the lesion can also mimic skin ulcerations in which typically long terms of treatment are common before healing occurs or before one seeks an alternative diagnosis. I have had two cases of amelanotic melanoma masquerading as a plantar diabetic foot ulcer and several colleagues have had similar experiences. The hesitancy to biopsy an ulcerated lesion also contributes to diagnosis in later stages.

   One interesting reported case of a amelanotic melanoma disguised as a diabetic foot ulcer adds another potentially problematic issue. This is because treatment for complications of diabetes may be immunosuppressive and therefore contribute to the advancing of the cancer.9

   In this case, a patient with type 2 diabetes with a longstanding stable right foot ulcer of 15 years underwent treatment with cyclophosphamide and prednisone for nephrotic syndrome over a seven-month period.9 The patient’s foot ulcer had previously received treatment from podiatric, vascular and orthopedic specialists over the years.

   Near the conclusion of immunosuppressive therapy that resolved the nephrotic syndrome, the patient’s right leg became edematous and a mass developed in her thigh. Although an initial examination determined the mass to be swollen lymph nodes, a biopsy revealed amelanotic melanoma. This subsequently forced a biopsy of the ulcer, which was amelanotic melanoma all along and apparently allowed to disseminate from the immunosuppressive therapy.

Comments

The literature states that melanoma in the foot is rare for a specific reason: feet have been neglected by "regular" doctors. Since podiatry has shifted into the surgical realm, I suspect that the incidence of melanoma in the foot will rise.

Be prepared to be removed from the course of treatment if a malignancy is detected. No matter how credentialed a podiatrist you might be, there is no place in the regimen of care rendered to the melanoma patient but for reassurance.

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