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Reviewing Cases Of Rare Pedal Melanomas
Malignant melanoma is the leading cause of mortality in skin cancer.1 Of all cutaneous malignant melanoma cases, approximately three to five percent of cases are found in the foot with the major cause of etiology being ultraviolet exposure.2
Acral lentiginous melanoma (ALM) is the most common type of melanoma in individuals with darker skin and those of Asian descent. ALM is generally not a result of exposure to ultraviolet irradiation, with the etiology yet to be determined.1 ALM appears on the palms of the hands, soles of the feet or under nails. ALM typically develops on the thumb or hallux, but it can occur on any fingernail or toenail. The first sign of ALM may be a “nail streak,” a dark stripe under the nail that sometimes extends to the nail fold which is called “Hutchinson sign,” although it should be noted that not all nail streaks are melanoma.3
Amelanotic melanoma (AM) accounts for approximately two to eight percent of all melanomas.4-6 AM is otherwise known as hypomelanotic as it has little or no melanin pigmentation, but may also present as pink or red macules, papules or nodules often with well-defined borders.4-6 AM often resembles many benign dermatologic lesions, which may lead to a considerable delay in diagnosis and a potentially worse prognosis.7
Subungual melanoma represents approximately two percent of melanomas, and of these subungual melanomas, 15 to 25 percent are amelanotic. Subungual melanoma is most commonly associated with the hallux toenail.9
When should lesions be biopsied? Any lesion noted to have change in color, shape, size, or elevation warrants attention. Changes in lesions are highlighted in the “ABCDE Guidelines” (Asymmetry, Border irregularity, Color change, Diameter greater than six mm, and Evolution or Elevation. The letter “E” for Evolution highlights the importance of changing lesion in appearance, size, shape, color, and symptoms.1
A number of biopsy methods have been described to diagnose malignant melanoma including punch biopsy, excisional biopsy, incisional biopsy or shave biopsy. Clinically, clear margins on excisional biopsy that encompass the entire width is preferred. For suspicious subungual lesions, the nail plate should be sufficiently removed to expose the underlying lesion and a biopsy should be performed with an adequate amount of atypical tissue.1
Melanoma in the foot poses a challenge to many clinicians as one tries to balance adequate oncologic resection while preserving limb function.
Case Study 1: Amelanotic Melanoma
A 66-year-old female presented to the office with what appeared to be a pyogenic granuloma to the dorsal distal aspect of the right hallux (see first photo). Upon the initial exam, the patient relayed a history of developing a small reddish lesion on her nail bed. This appeared as a pyogenic granuloma and we excised it.
Two months later she presented with a similar presentation. This time, we biopsied the lesion and sent it to pathology, which diagnosed amelanotic melanoma. Before performing any radical amputation, we would first attempt a wide excision of the lesion (see second photo). The patient then went to the operating room for an excisional biopsy (see third photo). The area was covered with a biologic dressing while awaiting pathology results (see fourth photo).
Pathology came back as a PT2Nx. The lesion showed that the medial margin demonstrated in situ melanoma remaining and that there were minimal clean margins on the plantar aspect of the prior specimen, defined as a Clark level 4 (see fifth photo). Oncology recommended that the patient have a distal Syme amputation and sentinel node biopsy (see sixth photo).
The patient underwent a partial hallux amputation with primary skin closure by the authors (see seventh photo). Additionally, general surgery performed sentinel lymph node biopsy.
After the second surgery, clear margins were reported by pathology with no metastases to lymph nodes, demonstrated by pathologic evaluation of the sentinel nodes.
Case Study 2: Right Heel Acral Lentiginous Melanoma
An 86-year-old male with a past medical history of hypertension and colon cancer presented to the office with a dark pigmented spot of skin to the posterior medial heel (see eighth photo). The lesion was irregular and approximately 2.5 cm in diameter. A punch biopsy indicated acral lentiginous melanoma.
The patient underwent a wide excision with one cm margins of the lesion to the right heel (see ninth photo) with application of Myriad biologic dressing (see tenth and eleventh photos) by podiatry. A general surgeon performed an inguinal lymph node biopsy. Pathology was negative for metastases to lymph node and margins were clear to right heel skin.
Conclusion
Wide excision of a lesion is the most important modality for melanoma. Additionally, having an oncologic team approach to biopsy lymph nodes and evaluate for metastases is essential. The primary goal of malignant melanoma is to achieve negative margins and prevent local recurrence after wide excision. The recommended margins for malignant melanoma ranges from 0.5 to one cm; however, many surgeons consider 0.5 cm margins the standard of care for excision of melanoma in situ. For this case presentation, one cm clear margins were maintained.
Treatment of cutaneous melanoma of the digits can be controversial. Previously, proximal amputations to the level of the metatarsophalangeal joint were thought to decrease recurrence and increase survivability; however, more recent literature disputes this.1,8 Surgeons are finding less radical excision should be performed for lesions to maintain maximum function, as recent literature shows that more distal levels of amputation do not compromise the survival or recurrence rate.1,8
This case study highlights the importance of evaluating the entirety of the nail plate and nail bed in patients with solitary nail dystrophy. Subungual melanoma may be confused with many other differentials including, but not limited to hematoma, paronychia or pyogenic granuloma. Although subungual amelanotic melanoma is rare, it is important to have as part of your differential especially if dystrophy involves a single toenail.9,10
Dr. Stuto is a Specialist and Fellow in Reconstructive Foot and Ankle Surgery within the Division of Podiatric Medicine and Surgery in the Department of Orthopaedics at the University of Texas Health San Antonio.
Dr. Rosen is the Chief Podiatric Surgery at Holy Name Medical Center. He is adjunct faculty and attending at University Hospital in Newark, NJ.
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2. Rashid OM, Schaum JC, Wolfe LG, et al. Prognostic variables and surgical management of foot melanoma: review of a 25-year institutional experience. ISRN Dermatol. 2011; 2011:384729.
3. Nakamura Y, Fujisawa Y. Diagnosis and management of acral lentiginous melanoma. Curr Treat Options Oncol. 2018; 19(8):42.
4. Jaimes N, Brauin RP, Thomas L:, Marghoob AA. Clinical and dermoscopic characteristics of amelanotic melanomas that are not of the nodular subtype. J Eur Acad Dermatol Venereol. 2012; 26(5):591–6.
5. Okhovat JP, Tahan SR, Kim CC. A pink enlarging plaque on the plantar foot: amelanotic aural lentiginous melanoma. Dermatol Online J. 2019; 25(1):1–4.
6. Pizzichetta MA, Talamini R, Stanganelli I, et al. Amelanotic⁄hypomelanotic melanoma: clinical and dermoscopic features. Br J Dermatol. 2004; 150(6):1117–24.
7. Strazzulla LC, Li X, Zhu K, et al. Clinicopathologic, misdiagnosis, and survival differences between clinically amelanotic melanomas and pigmented melanomas. J Am Acad Dermatol. 2019; 80(5):1292–8.
8. Nguyen JT, Bakri K, Nguyen EC, et al. Surgical management of subungual melanoma. Ann Plast Surg. 2013; 71(4):346–54. doi:10.1097/sap.0b013e3182a0df64.
9. Riahi RR, Cohen PR, Goldberg LH. Subungual amelanotic melanoma masquerading as onychomycosis. Cureus. 2018;10(3):e2307.
10. Winslet M, Tejan J. Subungual amelanotic melanoma: a diagnostic pitfall. Postgrad Med J. 1990; 66(773):200–202.
