Three Negro patients were evaluated for a diffuse dark pigmentation present from birth on all fingernails and toenails. Biopsies revealed numerous dopa-positive melanocytes of the nail matrix and pigmentation of the nail plate. The pigmentation was shown to be melanin, and it is postulated that this represents an extreme variant of the band-like pigmentation that is frequently seen in the nails of Negroes. Two hundred Negroes were evaluated for the presence of pigment anomalies, and pigmented bands were found to be as common as 77% in Negroes over the age of 20 years.
Leyden JJ, Spott DA, Goldschmidt H. Diffuse and Banded Melanin Pigmentation in Nails. Arch Dermatol. 1972;105(4):548-550. doi:10.1001/archderm.1972.01620070020007