The nail plate loses its transparency and looks white because of the presence of parakeratotic cells within its ventral aspect. True leukonychia is white opaque discoloration caused by diseases that disturb distal nail matrix keratinization and it presents with three morphologic variants:
Punctate leukonychia. The nail plate has small opaque white spots that move distally with nail growth and sometimes disappear before reaching the distal nail. It is caused by trauma and is most commonly observed in the fingernails of children.
Striate leukonychia. The nail plate has one or more transverse, opaque white, parallel lines that migrate distally with nail growth. It is frequently observed in the fingernails of women, due to matrix trauma secondary to manicures. Striate leukonychia may also occur in great toenails as a consequence of trauma from shoes. It is also typical of Mees’ lines, the white transverse bands seen in arsenic and thallium poisoning.
Diffuse leukonychia (porcelain nails, leukonychia totalis). The nail plate is completely or almost completely opaque and white. Diffuse true leukonychia is rare and may result from mutations in PLCD1 (encodes phosphoinositide-specific phospholipase C delta 1 subunit, a key enzyme in phosphoinositide metabolism expressed in the nail matrix) or GJA1 (encodes connexin 43). Patients with GJA1 mutations also have keratoderma and hypotrichosis. Bart–Pumphrey syndrome (also known as “Palmoplantar keratoderma with knuckle pads and leukonychia and deafness) in which patients have deafness, knuckle pads and palmoplantar keratoderma in addition to leukonychia, is due to mutations in GJB2 (encodes connexin 26).
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