Nodular nail unit melanoma mimicking a non-healing ulcer: Dermoscopic and reflectance confocal microscopic features.

Dear Editor, Nail unit melanoma (NUM) is a rare melanoma that originates from the nail unit apparatus. It usually has a lentiginous growth pattern, characterized clinically by an irregularly pigmented nail band. This peculiar growth pattern corresponds to an intraepidermal proliferation of atypical melanocytes in the nail matrix observed with histopathology, slowly evolving in months or years into an invasive tumor.1 However, NUM can mimic nodular melanomas, arising abruptly as a fast-growing ulcerated nodule. Often the lesion can lack an evident black pigment, thereby resembling benign conditions, such as warts, calluses, non-healing ulcers, or ingrown nails.1 These unspecific clinical features may cause diagnostic delay, the main motive for poor prognosis associated with nodular NUM.2 A 72-year-old man presented to our clinic with a bleeding lesion on the nail unit of his right thumb, which first appeared 6 months prior. The patient had been unsuccessfully treated with topical medications for a misdiagnosed ulcer. Clinically, the lesion presented as an ulcerated hypervascular red nodule, with the total avulsion of the nail plate (Figure 1A). The lesion was assessed with dermoscopy and reflectance confocal microscopy (RCM Vivascope 3000; MAVIG GmbH). Dermoscopic examination revealed an unspecific pattern, with diffuse milky-red areas, few atypical vessels, and an irregular peripheral rim of brown-black pigmentation and ulceration (Figure 1B). Lesion characteristics had the aspect of a probable melanocytic or non-melanocytic skin tumor, but we couldn't exclude the possible diagnosis of an inflammatory disease, due to the unspecific morphology of vessels and the diffuse ulceration. Pagetoid epidermal spreading with roundish hyperreflective cells (short white arrows) and ulceration (central image area) were clearly noticeable at RCM analysis (Figure 2A). Atypical nesting (long white arrows) was also evident (Figure 2B). The overall RCM pattern was suggestive of a malignant melanocytic lesion. Nail unit melanoma (NUM) diagnosis was confirmed at histology, with evident ulceration and a reported Breslow thickness of 2.4 mm (Figure 3). An oncogenic KIT mutation (p.L576P) was also detected during genetic analysis. Sentinel lymph node biopsy resulted in negative (pathological stage IIb).3 Any acral ulcerated nodule in the absence of clear benign features should be considered suspicious for melanoma. In our case, the clinical and dermoscopic presentation was unspecific, as only 20% of melanomas are amelanotic (with little or no pigment) and are commonly accepted as being difficult to diagnose.4 The presence of black pigment at dermoscopy examination offered a clue for melanocytic malignancy but this pattern was detected at the periphery of the lesion only. Other features were not specific and did not assist in differential diagnosis either for tumoral or inflammatory conditions. RCM was employed and proved useful in a timely and strong diagnostic suspicion of melanoma. Evidence of pagetoid spreading in the epidermis and atypical nesting in the dermis are both independent signs of malignant melanocytic lesions and should always warrant timely surgical intervention.5 Following the RCM assessment, the patient was urgently directed for surgical excision. Upon NUM confirmation, amputation of the distal phalanx was performed and the oncologist prescribed Pembrolizumab adjuvant therapy. RCM, together with dermoscopy, played an important role in this challenging clinical scenario and proved to be an important tool in preventing delayed diagnosis and treatment of a life-threatening disease, such as nodular NUM. Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.