Subungual amelanotic melanoma of the hallux : Review of the literature with a case report

MJ Tladi MBChB(UL Medunsa Campus), FCS (SA)Ortho, MMed(Orth Surg)(SMU) Dr George Mukhari Academic Hospital, Ga-Rankuwa, Pretoria and Sefako Makgatho Health Science University, Ga-Rankuwa, Pretoria, South Africa NP Saragas MBBCh(Wits), FCS(SA)Ortho, MMed(Ortho Surg)(Wits) Netcare Linksfield Orthopaedic Sports & Rehabilitation Centre (Clinic), Johannesburg and Orthopaedic Department, University of the Witwatersrand, Johannesburg, South Africa PNF Ferrao MBChB(Pret), FCS(SA)Ortho Netcare Linksfield Orthopaedic Sports & Rehabilitation Centre (Clinic), Johannesburg and Orthopaedic Department, University of the Witwatersrand, Johannesburg, South Africa A Strydom MBBCh(Wits), FCS(SA)Ortho, MMed(Ortho Surg)(Wits) Orthopaedic Department, University of the Witwatersrand, Johannesburg, South Africa


Introduction
Subungual melanoma was first fully described in 1886 by Sir Hutchinson, 1 yet in the 21st century this condition is still misdiagnosed resulting in a high morbidity and mortality.The famous reggae singer, Bob Marley, succumbed to an aggressive subungual malignant melanoma of the hallux at the age of 36 years. 2,3][6] The patient was referred to a dermatologist who performed a biopsy.The diagnosis of an amelanotic melanoma was made upon histology.There was no history of previous trauma to the nail or positive family history of melanoma (5%-10% reported incidence of a positive family history). 7

Examination
Examination revealed a generally well elderly Caucasian female.A granulomatous type lesion, measuring 2 cm by 1.5 cm, was present overlying the nail bed of the right hallux (Figures 1a and 1b).The lesion was tender to palpation.No ipsilateral inguinal lymph nodes were palpable and the foot was neurovascularly intact.

Special investigations
No bony involvement was evident on plain radiographs (Figure 2).A PET CT scan (Figure 3) showed no metastases.

Management
Once the case was discussed with an oncologist, informed consent was obtained from the patient to perform a partial amputation of the hallux.The hallux was amputated at the level of the mid-shaft of the proximal phalanx, allowing for at least a 15mm clear margin from the tumour edge (Figures 4a and 4b).The histology report once again confirmed the amelanotic melanoma, stage IIb (Figure 5), with 20 mm clear margins.The patient was referred to the oncology unit for further treatment as required.

Discussion
Pigmentation of the toenails can be due to benign, systemic disease manifestation or malignant conditions, with melanoma being one of the rare malignancies (3.2% of foot and ankle tumours). 8,9Generally there are four types of melanoma, with acral melanoma affecting the hands and feet.This usually occurs in black African and Asian populations contrary to the other types which are more common in fair-skinned populations. 7,9][10][11][12] Table II shows all case reports of subungual amelanotic melanoma affecting the hallux, all of which had a delay in the diagnosis.Only five case reports were identified after an extensive search of the English literature.
The incidence of subungual melanoma is high in black Africans and Asians between the ages of 50 to 70 years.Males and females are equally affected. 4,7,8Our case, however, was in an 80-year-old Caucasian female.Upon reviewing the literature reporting on subungual amelanotic melanoma of the hallux, all patients were Caucasian, with 60% being female.We thus propose that subungual amelanotic melanoma actually has a higher incidence in Caucasian females.Symptoms in most cases are vague and the lesion resembles other conditions.The ABCDEF rule was described by Levit et al. to reduce misdiagnosing subungual melanomas and improve early detection (Table III). 16Hutchinson's sign describes a black discoloration of the proximal nail fold which is suggestive of subungual melanoma.This sign has inherent flaws as it has no role in amelanotic melanoma due to absence of pigmentation, as was seen in our patient.Hutchinson's sign can also be associated with Laugier-Hunziker syndrome, ethnic pigmentation, infections or the use of certain medications.When present, however, it is indicative of a poor prognosis. 8,16anagement of subungual melanoma of the hallux is usually amputation of the digit, which can cause functional and emotional problems, such as in the case of Bob Marley who refused amputation due to religious reasons and only agreed to local excision of the tumour. 2,4,17is ultimately resulted in metastasis and his demise.As the diagnosis is often delayed with resultant local invasion, amputation is the recommended management. 17he tissue must be sent for histology and the report should include: histological type, presence of ulceration, presence of infiltrative lymphocytes, regression, microsatellite lesions, margins, micro-staging (tumour thickness according to Breslow and level of invasion according to Clark) which are helpful with final staging. 7,10Melanoma is staged according to the American Joint Committee on Cancer (AJCC). 7A sentinel lymph node (SLN) biopsy is recommended for melanomas stage 1b and above. 7ecurrence of foot melanoma is 37% at approximately 3 years and survival rate after recurrence is shorter than 41 months. 18Prognosis of subungual melanoma in general is poor.The 5-year survival rate of subungual melanoma of the toe is 40% as compared to 72% in the finger. 17The 5-year survival rate for melanoma in general is 74.3% in the foot and 85.2% in the leg. 18The survival rate is directly related to the staging by the AJCC.

Conclusion
Subungual melanoma is rare, especially in the Caucasian population.However, the incidence of subungual amelanotic melanoma has only been reported in Caucasians, contrary to other subungual melanomas which occur mainly in black Africans and Asians.There is also a predilection for the female gender.We thus propose that subungual amelanotic melanoma occurs mainly in elderly Caucasian females.The diagnosis is often delayed, as it can mimic a variety of hallux nail conditions.Due to lack of pigmentation, amelanotic melanoma poses a huge dilemma in diagnosis.A high index of suspicion is thus imperative.The use of the ABCDEF rule can help in increasing awareness and reducing the delay in diagnosing subungual amelanotic melanoma.An incisional biopsy should be performed early.Once histological confirmation is made, amputation is the treatment of choice and the patient should be referred to an oncology unit for further management according to the AJCC staging.

table iii : Steps to follow when suspecting subungual melanoma
EExtension: Extension of pigment to involve proximal or lateral nail fold (Hutchinson's sign) or free edge of nail plate F Family or personal history: Of previous melanoma or dysplastic naevus syndrome