Case Reports

Pigmented Squamous Cell Carcinoma Presenting as Longitudinal Melanonychia in a Transplant Recipient

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We report the case of a 62-year-old black man who was on a maintenance immunosuppressive regimen that included mycophenolate mofetil and cyclosporine following renal transplantation 9 years prior. He presented to the dermatology department for evaluation of a pigmented longitudinal streak on the left third finger adjacent to the lateral nail fold that had been present for several months. He noted that the streak was increasing in size, and his fingertip had recently become tender. The pigmented band was biopsied, and histopathology showed atypia of the epidermis consistent with pigmented squamous cell carcinoma (pSCC).

Although subungual melanoma is the most concerning cause for longitudinal melanonychia, there are a number of other potential causes, including fungal infection, trauma, benign melanocytic lesions, or other cutaneous malignancies. Pigmented squamous cell carcinoma is another potential cause of longitudinal melanonychia and should be included in the differential diagnosis, particularly in individuals with skin of color or those who are immunosuppressed. This article highlights features of the clinical presentation of pSCC presenting as longitudinal melanonychia that mimicked the clinical appearance of subungual malignant melanoma in a renal transplant recipient. A review of pSCC and its associated risk factors also is provided.

Practice Points

  • Risk factors for the development of pigmented squamous cell carcinoma (pSCC) include older age, male sex, and use of immunosuppressant medications.
  • Subungual pSCC can present as longitudinal melanonychia and should be considered in the differential diagnosis for melanonychia in patients with skin of color or those who are immunosuppressed.



Case Report

A 62-year-old black man presented for examination of a dark longitudinal streak located adjacent to the lateral nail fold on the third finger of the left hand. The lesion had been present for several months, during which time it had slowly expanded in size. The fingertip had recently become tender, which interfered with the patient’s ability to work. His past medical history was remarkable for end-stage renal disease secondary to glomerulonephritis with nephrotic syndrome of unclear etiology. He initially was treated by an outside physician using peritoneal dialysis for 3 years until he underwent renal transplantation in 2004 with a cadaveric organ. Other remarkable medical conditions included posttransplantation diabetes, hyperlipidemia, and gout. His multidrug regimen included 2 immunosuppressive medications: oral cyclosporine 125 mg twice daily and oral mycophenolate mofetil 250 mg twice daily.

A broad, irregular, black, pigmented, subungual band was noted on the left third finger. The lesion appeared to emanate from below the nail cuticle and traveled along the nail longitudinally toward the distal tip. The band appeared darker at the edge adjacent to the lateral nail fold and grew lighter near the middle of the nail where its free edge was noted to be irregular. A slightly thickened lateral nail fold with an irregular, small, sawtoothlike hyperkeratosis and hyperpigmentation also was noted (Figure 1).

Figure 1. Pigmented squamous cell carcinoma presenting as a broad, black, pigmented, subungual band emanating longitudinally from the nail bed toward the distal tip of the left third finger.

Subungual melanoma, onychomycosis, squamous cell carcinoma (SCC), and a verruca copresenting with onychomycosis were considered in the differential diagnosis. The patient underwent nail avulsion and biopsy of the nail bed as well as the nail matrix. Histopathology was notable for malignant dyskeratosis with a lack of nuclear maturation, occasional mitoses, multinucleation, and individual cell keratinization (Figure 2). Immunostaining for S100 was negative, while staining for cytokeratins AE1/AE3 was positive. Deposition of melanin pigment in the malignant dyskeratotic cells was noted. Periodic acid–Schiff staining identified pseudohyphae without invasion of the nail plate. A diagnosis of pigmented SCC (pSCC) was made. The patient’s nail also was sent for fungal cultures that later grew Candida glabrata and Candida parapsilosis.

The patient underwent Mohs micrographic surgery for removal of the pSCC, which was found to be more extensive than originally suspected and required en bloc excision of the nail repaired with a full-thickness skin graft from the left forearm. The area healed well with some hyperpigmentation (Figure 3).

Figure 2. Nail matrix biopsy showed characteristic papillary architecture, malignant dyskeratosis with a lack of nuclear maturation, occasional mitosis, individual cell keratinization, and prominent pigmentation (H&E, original magnification ×160).
Figure 3. Well-healed site of a pigmented squamous cell carcinoma with hyperpigmentation following Mohs micrographic surgery and a full-thickness skin graft.

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