Keys To Diagnosing Metastatic Melanoma In The Foot And Ankle

Author(s): 
Christopher Witt, DPM, and Steven Geary, DPM

Given that melanoma in the foot is commonly misdiagnosed, these authors present the case of a 45-year-old with a history of multiple melanotic lesions and emphasize the importance of early diagnosis.

A review of the literature reveals that melanoma is the sixth most common type of cancer in the United States and we commonly misdiagnose it in the foot and ankle.1 Melanoma can arise from a preexisting nevus or develop de novo on the skin. The lifetime risk for men developing the disease is 1:120 and the risk is 1:95 for women.2

   Foot and ankle lesions represent approximately 3 to 15 percent of all cutaneous melanomas.2 In a review of 63 cases, 29 percent of lesions were on the dorsum of the foot, 19 percent on the heel, 17 percent on the plantar aspect of the foot, 17 percent on the ankle and 13 percent at the digits.3 Forty-seven of these patients were women and 16 were men.

   There are four major types of melanoma. Superficial spreading melanoma is the most common and most frequently occurs on the dorsum of the foot.2 Acral lentiginous melanoma is the only type that arises equally across all skin types, representing about half of the melanoma occurring on the hands and feet.2 Nodular melanoma is the most frequently occurring melanoma in the older population. Lentigo maligna melanoma occurs almost exclusively on the face and neck due to sun damage.2

   There are also two types of nail unit melanoma, longitudinal melanonychia and amelanotic. Nail unit melanoma has the worst prognosis of all melanomas and represents 1.4 percent of melanomas.2 The five-year survival rate is 88 percent with Breslow thickness less than 2.5 mm and this decreases to 44 percent when the Breslow thickness is greater than 2.5 mm.2

Pertinent Guidelines For Diagnosing Melanoma

It can be difficult for one to distinguish between a nail unit melanoma and a dystrophic nail. One of the principles of nail unit anatomy is that melanocytes only occur on the matrix and nail folds, not the nail bed. This means that if there is a pigment change in only the nail bed, it is not a melanoma. A source of pigment that is clear proximally is usually a hematoma. A pigmented area that is present only within the nail bed and has a normal nail matrix and nail fold is also not likely to be melanoma.

   The shape of the change in pigment can also be helpful in distinguishing a melanoma from a hematoma. Pools of irregular shaped pigment are most likely a hematoma whereas a well-organized linear band with consistent width that begins in the matrix is likely to be a melanonychia. In dark-skinned patients, hyperpigmentation is more likely to occur in the nail unit with an increase in age. The more common causes for this are trauma, fungus and lichen planus.

   One of the classic clinical findings for nail unit melanoma is Hutchinson’s sign. A true Hutchinson's sign is when pigment is visible on the nail fold or distal pulp of the digit. This usually results in a poorer prognosis for the individual. We often misdiagnose this as a pseudo Hutchinson’s sign, which is pigment visible in the clear edges of the nail fold as it becomes the cuticle. Another rule of thumb is that if the pigment becomes wider more proximally, this is also most likely melanotic.2

   The common misdiagnoses for melanoma of the foot and ankle include paronychia, subungual hematoma, pyogenic granuloma, neuropathic ulceration and tinea pedis. There are multiple mnemonics that we can use as tools to help determine the probability of melanoma.

   One mnemonic is ABCDE, which has been in use for years for melanoma detection for the entire body. It stands for:2

• Asymmetry
• Borders of irregularity
• Colors
• Diameter greater than 6 mm
• Evolution

   CUBED is a relatively new acronym tailored for lesions of the foot and ankle. It stands for:2

• Colored lesion
• Uncertain diagnosis
• Bleeding lesions (including chronic granular lesions)
• Enlargement of the lesion despite treatment therapies
• Delay in healing beyond two months.

What The Literature Reveals About Recurrence And Survival Rates

Rates of recurrence vary depending on the literature. In one study, researchers found 36 percent recurrence rates for patients who received local excision and 0 percent for patients treated with digital amputations.4 Overall, they found lesions between 1 to 4 mm had the highest risk of recurrence but after 75 months, lesions greater than 4 mm had a low risk of recurrence. The study authors found no correlation among the histology, thickness and site of origin or mitotic index with recurrence rate. The researchers also found the rate of recurrence with patients with foot melanoma and poor prognostic factors had excellent survival rates in comparison to patients with melanoma of the trunk or extremities.

   Another study found that the five-year overall survival rate for melanoma of the foot and ankle was 63 percent and 51 percent for 10 years.5 In the study, 32 patients with plantar or subungual lesions had a mean duration of survival of 47 months in comparison to 72 months for the 28 patients with foot or ankle lesions. Fifteen patients who had a misdiagnosis had a mean duration of survival of 22 months in comparison to 67 months for 45 patients with correct diagnosis. Another study found that 33 percent of patients with acral lentiginous melanoma of the foot or ankle initially had the wrong diagnosis, and the average time for correct diagnosis was 13.5 months.6

   chronic, intractable pain. The survival rate is also drastically lower. In a study reviewing 11 patients with osseous metastasis of melanoma, researchers found that the mean time from initial diagnosis of melanoma to radiographic evidence of osseous metastasis was 9.75 months.7 After radiographic changes were visible, the mean survival time was 5.67 months. The treatment that one renders at this point is usually supportive at best. The priorities are to prevent fractures and provide pain relief.

What You Should Know About The Patient Presentation

In 2008, a 45-year-old male patient presented to the emergency department after a two-week history of a palpable mass to the right anterior-lateral mid-thigh. Six years earlier, the patient had wide local excision of two suspicious lesions of the back and right calf. The lesion on the back had melanoma and the patient subsequently had an excision of the right axillary lymph nodes. The lesion on the calf later recurred and a second biopsy revealed melanoma as well. The patient reported no further complications until this visit.

   A biopsy of the new lesion on the thigh also revealed melanoma. The patient then went to oncology for treatment including interleukin and radiation therapy.

   The patient then presented to the emergency department for pain to the left anterior ankle and mid-leg in 2010. He denied any trauma to the area. There was no limitation of ankle joint range of motion but there was pain throughout. X-rays, magnetic resonance imaging (MRI), computed tomography (CT) and bone scans found metastases to the left lower leg, clavicle, sternum, liver and brain. X-rays revealed a lytic lesion to the proximal fibula and MRI of the ankle showed an osteochondral lesion of the left talus.

   The patient wore a supportive brace but I lost him to follow-up. After a review of medical records, the patient continued to see oncology for painful lesions that developed in the upper extremities as well as recurrent headaches. The patient received further radiation therapy until his death in 2011.

In Conclusion

Melanoma is the sixth most common cancer in the United States. There will be an estimated 76,250 new cases this year with 9,180 deaths.1 Lesions of the feet and ankle are notoriously misdiagnosed. Without early detection and treatment, survival rates plunge for these patients.

   The patient in our case report was receiving primary treatment from an oncologist. By the time we saw him in the podiatry clinic, palliative care was the only treatment available for his chronic pain. Our patient died one year later. It is of paramount importance to identify these lesions and provide proper treatment as early as possible.

   Dr. Witt is a podiatry resident at the Captain James A. Lovell Federal Health Care Center in North Chicago, IL

   Dr. Geary is a podiatry attending affiliated with the Captain James A. Lovell Federal Health Care Center in North Chicago, IL.

References

1. American Cancer Society: Cancer Facts and Figures 2012. American Cancer Society, Atlanta, GA, 2012. Available at www.cancer.org/acs/groups/content/@epidemiologysurveilance/documents/document/acspc-031941.pdf . Accessed Jan. 23, 2014.
2. Bristow IR, Berker DA, Acland KM, et al. Clinical guidelines for the recognition of melanoma of the foot and nail unit. J Foot Ankle Res. 2010; 3:25.
3. Bates B. Gender differences seen in foot, ankle melanoma. Family Practice News. Available at: www.familypracticenews.com/search/search-single-view/gender-differences-... Published Nov. 1, 2006. Accessed January 27, 2014.
4. Rashid OM, Schaum JC, Wolfe LG, et al. Prognostic variables and surgical management of foot melanoma: a review of 25-year institutional experience. ISRN Dermatol. 2011; 384729.
5. Fortin PT, Freiberg AA, Rees R, Sondak VK, Johnson TM. Malignant melanoma of the foot and ankle. J Bone Joint Surg Am. 1995; 77(9):1396-1403.
6. Bristow I, Acland K. Acral lentiginous melanoma of the foot and ankle: a case series and review of literature. J Foot Ankle Res. 2008; 15(1):11.
7. Huang KY, Wang CR, Yang RS. Rare clinical experiences for surgical treatment of melanoma with osseous metastases in Taiwan. BMC Musculoskeletal Disorders. 2007; 8:70.

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