Nail Signs due to abnormal nail matrix function – ture leukonychia 真性白甲

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).

leukonychia

真性白甲指甲板失去其透明度并且看起来是白色的，因为在其腹侧存在角化不全细胞，是远端指甲基质角质化引起的疾病。它包括三种形态：点状白甲、条纹白甲、全白甲。

点状白甲可能是外伤导致，但是大多在儿童指甲常见，实属正常。
条纹白甲在做修甲美甲的女性中多见，也可能是砷、铊重金属中毒的表现。
全白甲是基因变异导致，如Bart–Pumphrey综合症 (掌跖角化病与指关节垫和白甲和耳聋)。

Reference:

  1. Antonella Tosti, Bianca Maria Piraccini. In: Jean Bolognia Julie Schaffer Lorenzo Cerroni, editors. Dermatology: 2-Volume Set 4th Edition. Elsevier; 2017. p1204-1205.
  2. Baran R, Dawber RPR. Physical signs. In: Baran R, Dawber RPR, eds. Diseases of the Nails and Their Management, 2nd edn. Oxford: Blackwell Science, 1994:72.
    Marino MT. Mees’ lines. Arch Dermatol 1990;126:827–8
  3. Mautner GH, Lu I, Ort RJ, Grossman ME. Transverse leukonychia with systemic infection. Cutis 2000;65:318–20.
  4. Albright SD, Wheeler CE. Leukonychia: total and partial leukonychia in a single family with review of the literature. Arch Dermatol 1964;90:392–9.
  5. Grossman M, Scher RK. Leukonychia: review and classification. Int J Dermatol 1990;29:535–41