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).
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).