Leukonychia striata longitudinalis occurred in two patients, in which a longitudinal white streak persists in a finger nail for several years. In the first case the white streak is attributed to the presence of abnormal cornified cells in the nail plate, accompanied with parakeratotic hyperplasia of the nail bed epidermis. In the second case the white streak is attributed just to parakeratotic hyperplasia of the nail bed epidermis upwards into the nail plate in absence of any abnormal cornified cells in the nail plate. The disturbance is probably due to nevoid changes at the distal nail matrix beneath the leukonychia. It is presumed that incomplete keratinization of the lower nail plate in the former case as well as its absence or decrease in the latter causes a secondary activation in the nail bed epidermis.
Higashi N, Sugai T, Yamamoto T. Leukonychia Striata Longitudinalis. Arch Dermatol. 1971;104(2):192–196. doi:10.1001/archderm.1971.04000200080014
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