Unmasking subungual melanoma: An aggressive presentation in a young male with longstanding longitudinal melanonychia

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A 17-year-old male presented to our outpatient department with blackish discoloration along with destruction of his left index finger nail for the past 5 months. The lesion had initially appeared as an inconspicuous brown to black longitudinal pigmented streak 5 years ago, which he had ignored. Over the past few months, it showed rapid progression, extending to the proximal and lateral nail folds, followed by destruction of the nail plate, associated with pain and occasional mucopurulent discharge. This was followed by progressively increasing swelling of the distal left index finger. He denied any history of trauma, chronic irritation or family history of skin malignancy.

In Figure 1, cutaneous examination revealed mildly tender swelling of the left index finger distal to the interphalangeal joint [Figure 1a], with dystrophic, hyperpigmented nail plate and mucopurulent discharge [Figure 1b]. Hyperpigmentation of the proximal nail fold, hyponychium and periungual area (positive Hutchinson’s sign) was noted. Systemic examination was unremarkable, and there was no regional lymphadenopathy.

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Figure 1:

(a and b) Total nail dystrophy and swelling of the left index finger, with mucopurulent discharge and crusting. (c) Dermoscopy showing a disorganised pigment network with heterogeneous pigmentation and disruption of the parallel ridge pattern (DermLite DL4, polarised mode, ×10). (d) Post-operative image showing partial amputation at the proximal interphalangeal joint of the left index finger.

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Dermoscopy revealed disorganised, heterogeneous pigmentation, pigment extension to the nail folds (Hutchinson’s sign) and loss of the parallel ridge pattern [Figure 1c], raising suspicion of subungual melanoma (SUM). A punch biopsy from the matrix revealed melanocytic proliferation with marked anisonucleosis, atypical mitoses and admixed melanophages suggestive of malignant melanoma of acral lentiginous subtype [Figure 2]. Immunohistochemical findings showed strong SOX10 positivity, supporting melanocytic differentiation. The presence of preferentially expressed antigen in melanoma (PRAME) expression, although weak, further supported the diagnosis of melanoma [Figure 3]. A staging workup, including chest radiography, abdominal ultrasound, contrast-enhanced computed tomography of the chest, abdomen and pelvis and a positron emission tomography initiated to assess for metastatic spread, showed no evidence of distant metastasis. Following a multidisciplinary discussion with surgical oncology, the patient underwent complete excision of the entire lesion along with disarticulation at the proximal interphalangeal joint [Figure 1d]. Surgical pathology confirmed tumour-free margins. The patient remains on regular follow-up, with no evidence of recurrence or complications at 1-year post-surgery.

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Figure 2:

(a) Histopathological sections showing multinucleated bizzare cells (red arrow). (b) Fibrocollagenous stroma with cellular atypical melanocytic proliferation. (c) Moderate to marked nuclear anisonucleosis noted. H&E: Hematoxylin and eosin.

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Figure 3:

(a) Immunohistochemical staining for PRAME showing nuclear immunoreactivity in few cells. (b) Strong diffuse immunoreactivity noted with SOX-10 immunostaining.

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SUM is a distinct variant of acral lentiginous melanoma originating within the nail apparatus. Although rare, it accounts for approximately 0.7–3.5% of all malignant melanomas globally.^[1,2] More common in the non-Caucasian population, SUM is unrelated to ultraviolet exposure and typically presents in the sixth to seventh decades, with earlier onset in females. The thumb and great toe are the most frequently affected sites, involved in 75–90% of cases.^[3] SUM arises from melanocytes in the nail matrix, which are fewer than in the epidermis. Pathological activation of melanocytes in the nail matrix leads to their neoplastic proliferation, with distal migration along the nail unit, resulting in characteristic clinical features such as longitudinal melanonychia, nail dystrophy and pigment dispersion.^[2,3] This case showed a similar pattern with delayed presentation, as reported in the Indian series, often in males.^[3]

The incidence of melanoma has risen in recent decades, with improved survival linked to earlier detection. SUM, however, remains challenging to diagnose due to its insidious onset and frequent clinical misattribution in early stages. Early lesions may mimic benign conditions such as trauma, nevi, pyogenic granuloma, onychomycosis or hematoma, especially in younger patients.^[3,4] Longitudinal melanonychia, as observed in this case, is a classic early feature of SUM, yet its clinical significance is often underrecognised. Dermoscopy aids early detection by revealing suggestive features such as irregular band patterns, pigment extension to the nail folds (Hutchinson’s sign) and disruption of the parallel ridge pattern.^[4] Histopathology remains the diagnostic gold standard. In this case, a punch biopsy from the most suspicious area enabled definitive diagnosis, highlighting the importance of selecting an appropriate biopsy site.^[4,5] Effective management requires a multidisciplinary approach. Treatment typically involves wide local excision or amputation based on tumour depth, with sentinel lymph node biopsy recommended for lesions >1 mm thick.^[6] Prognosis is poorer than other melanoma subtypes due to delayed diagnosis, with 5-year survival rates ranging from 16% to 87%. Early detection through increased awareness is essential to improve outcomes.^[7]

This case highlights the diagnostic challenge of SUM, particularly in younger patients, where it may often be overlooked or misdiagnosed as a benign nail pathology. Early signs such as longitudinal melanonychia and Hutchinson’s sign warrant prompt evaluation. Dermoscopy and targeted biopsy enabled timely diagnosis, and surgical management may lead to a favourable outcome. A high index of suspicion and early recognition are crucial to improve prognosis.