A Case of Pigmented Longitudinal Melanonychia: JAMA
A man in his 40s presented to the dermatology clinic for evaluation of a new pigmented lesion on his left second toenail. The lesion first appeared 12 months before presentation and was progressively growing. This was his first time presenting to a physician for this problem, and no prior treatments had been attempted. The lesion was asymptomatic. He was otherwise well and denied any fevers or weight loss.

Clinical examination revealed a dark brown longitudinal pigment band covering the full length of the toenail of the left second digit with corresponding nail thickening over the pigmented band. The pigment was the same width throughout the band and extended to the proximal nail fold. No other nail or skin lesions were found at the time of examination. A biopsy specimen was obtained from the nail plate and nail matrix and stained with hematoxylin-eosin.

Histologic examination of the nail plate and nailmatrix showed bland spindle cell proliferation within the nail matrix with invaginations of the epithelium. No melanocytic lesions were observed, and immunostaining was negative for S100 and CD34. Intracorneal hemorrhage and adjacent verrucous hyperkeratosis were present.

Based on the histologic findings of villous fibroepithelial projections into the nail plate without melanocytic proliferation or keratinocyte atypia, a diagnosis of pigmented onychomatricomawas made. The nail was surgically removed to fully excise the lesion after the original biopsy. At approximately 3 months of follow-up, the patient was doing well and without evidence of recurrence of the lesion.

Final Dx: Pigmented onychomatricoma

Read more here: https://jamanetwork.com/journals/jamadermatology/article-abstract/2696637