When A Suspected Granuloma Turns Out To Be Acral Lentiginous Melanoma

Acral lentiginous melanoma can be particularly difficult to diagnose in the nail, as it classically presents as a black-brown longitudinal band typical of longitudinal melanonychia. However, these authors note with this case study that alternate presentations are possible and emphasize the importance of a high index of suspicion and early biopsy in diagnosing these masquerading lesions.

Malignant melanoma of the foot is rare but serious as it often goes unnoticed until it reaches advanced stages. Melanoma is most common in people between the ages of 30 to 60.¹ Approximately three to 15 percent of all melanomas occur in the foot.² Melanoma is the least common type of skin cancer yet the most deadly due to metastasis if it is not detected early.³ Clinical staging of melanoma is the most important indicator of survival rate.¹ The five-year survival rate for local melanomas is 98 percent. However, with distant metastasis the survival rate drops to 23 percent.³

Acral lentinginous melanoma involves palms, soles, nail beds and periungual surfaces.⁴ Unlike other melanomas that are caused by ultraviolet light, acral lentiginous melanoma is caused by a genetic risk factor as opposed to sun exposure.⁴ Acral lentiginous melanoma is the least common type of melanoma but is more common in individuals with more darkly pigmented skin such as African-Americans and those of Asian descent.⁵

In particular, clinicians may confuse subungual melanoma with trauma or fungus, leading to frequent delays with diagnosis and treatment. Mnemonics such as CUBED (color, uncertain diagnosis, bleeding, enlargement, delay) and ABCDE (asymmetry, border, color, diameter, evolution) can aid in clinician detection.⁶ However, for the best prognosis, the time from onset to diagnosis to treatment should be minimal.

In the following case, we will discuss acral lentiginous melanoma presenting as a granuloma on the hallux.

Keys To The Case Presentation

A 62-year-old Caucasian male presented to our office in January 2018  after a having a left hallux toenail blood blister since July 2017. He specifically recalled an incident of bleeding from the toenail in October. His mother had a history of leukemia. He denied any tobacco use.

During the initial consultation, the patient reported pain as one out of 10 on the verbal numerical pain scale. During the clinical exam, we noted a left hallux nail bed granulomatous lesion (1.5 cm x 1.5 cm) at the medial one-half of the nail. The nail plate was intact but loose, and there was mild pain on palpation.

An X-ray series obtained in the office did not reveal any bony involvement. For the initial treatment plan, we discussed excision of a suspected granuloma with nail avulsion and possible V-to-Y skin advancement.

We subsequently performed an excisional biopsy of the lesion and a nail matrixectomy. Upon excision of the lesion, we noted multiple hyper-pigmented lesions and proceeded to excise these lesions. We sent a second specimen to pathology.  

The pathologic revealed acral lentiginous melanoma with a depth of 4.6 mm. The pathologist initially staged this condition as a Clark’s IV lesion, which was positive for ulceration without angiolymphatic invasion and a stage pT4b pNx pMx. The tumor cells were positive for Mart-1 and S-100, and negative for p63. At this point, we referred the patient to a surgical oncologist at a local cancer center. Subsequent ultrasound of the popliteal and inguinal lymph nodes did not reveal any abnormalities.

The patient then had surgical excision of the left hallux to the level of the metatarsophalangeal joint with a regional lymph node biopsy under general anesthesia with a laryngeal mask airway. Pathology revealed residual melanoma with a depth lesser than the original report and clear surgical margins. The four inguinal nodes were all negative for malignancy.

The surgical oncologist recommended biannual full body examinations performed by a dermatologist and a lymph node ultrasound every six months for the patient.

Final Thoughts

Acral lentiginous melanoma is a rare subtype of melanoma, which comprises up to 10 percent of all melanoma cases. It is of particular concern because it is defined as one of the most aggressive subtypes.6 This condition has a higher incidence in individuals with darker pigmentation, accounting for 18 percent of recorded incidences.6 Acral lentiginous melanoma is characterized by a radial lentiginous growth followed by a vertical invasive stage.7 Acral lentiginous melanoma can be particularly difficult to diagnose in the nail as it classically presents as a black-brown longitudinal band typical of longitudinal melanonychia.6 It is not until the later stages that friable nodules with outward proliferation appear.8   

In this particular case of a Caucasian 62-year-old male, acral lentiginous melanoma presented with characteristic features of a benign pyogenic granuloma in the hallux nail bed that went undiagnosed for months. Without a biopsy proving otherwise, one could easily misdiagnose this lesion for a very common and classic benign pathology. With that in mind, there is a potential for delay in proper treatment without early accurate diagnosis, thus contributing to poor prognosis.

This case emphasizes the significance of biopsies for ulcerative lesions or those resistant to standard treatment. We bring this case to light to relay the importance of adding melanoma to the differential diagnosis when dealing with ulcerative lesions of the foot.  

Dr. Brennan is in private practice with Healthy Feet Podiatry, with multiple office locations in Florida.

Dr. Sklencar is currently a third-year resident at James A. Haley VA Hospital in Tampa, Florida.

1. Malay DS, Ugrinich M. Skin lesions. In: Southerland JT, ed. McGlamry’s Comprehensive Textbook Of Foot And Ankle Surgery. 4^th ed. Philadelphia, Wolters Kluwer, 1375-1379.
2. Nichols H. What to know about foot melanoma. Medical News Today. Available at: https://www.medicalnewstoday.com/articles/79115.php. Updated July 27, 2019. Accessed September 13, 2019.
3. Key statistics for melanoma skin cancer.  American Cancer Society Website. Available at: https://www.cancer.org/cancer/melanoma-skin-cancer/about/key-statistics.html. Updated August 14, 2019. Accessed September 13, 2019.
4. Acral Lentiginous Melanoma (ALM). AIM At Melanoma Foundation Website. Available at: https://www.aimatmelanoma.org/melanoma-risk-factors/melanoma-in-people-of-color/acral-lentiginous-melanoma-alm/. Accessed September 13, 2019.
5. NCCN guidelines for patients: melanoma. National Comprehensive Cancer Network Website. Available at: https://www.nccn.org/patients/guidelines/melanoma/files/assets/common/downloads/files/melanoma.pdf. Accessed September 13, 2019.
6. Gumaste P, Penn L, Cohen N, Berman R, Pavlick A, Polsky D. Acral lentiginous melanoma of the foot misdiagnosed as a traumatic ulcer. J Am Podiatr Med Assoc. 2015;105(2):189-194.
7. Coleman WP, Loria PR, Reed RJ, Krementz ET. Acral lentiginous melanoma. Arch Dermatol. 1980;116:773-776.
8. Desai A, Ugorji R, Khachemoune A. Acral melanoma foot lesions. Part 2: clinical presentation, diagnosis, and management. Clin Exp Dermatol. 2018;43(2):117-123.