By Gary M. White, MD
Leukonychia means white nail. Leukonychia may be true (TL) or pseudo (apparent). TL is caused by an abnormality of the nail plate that originates from the nail matrix. In other words, the nail grows out white because the nail root (matrix) is temporarily disrupted or permanently defective. TL is most commonly acquired (and partial) and presents with white spots or transverse lines on the nails (see leukonychia punctata). It is thought that trauma temporarily disrupts the formation of the nail plate. There is an inherited form of true leukonychia which is rare. This form is almost always complete (involves the entire nail) and has its onset congenitally or at a very young age.
Pseudo (apparent) leukonychia (PL) is usually acquired and may result from an abnormality of the nail plate (e.g. onychomycosis) or the nail bed, e.g. onycholysis, onychomycosis, Terry's nails.
The inherited type of TL is usually autosomal dominant. Genetic linkage studies of one family with hereditary subtotal leukonychia indicated a defect in a gene residing on chromosome 12q13. As the type II keratins map within this chromosomal interval, it is possible that a mutation in one of these keratin genes may be a cause of the hereditary leukonychia. The white appearance of nails in this family seemed to be due to an abnormal keratinization of cells originating from the proximal nail matrix, leading to the presence of abundant intracellular vacuoles and to a lesser compactness of keratins.
When inherited (genetic defect), the nails of TL are usually completely white, with onset at birth although onset in childhood has been documented.
When TL is partial and acquired, it may take on several forms, the most common being:
Causes of transverse leukonychia are legion and include: malignancies, various drugs (e.g. doxorubicin, vincristine, cyclophosphamide, isotretinoin, penicillamine) leprosy, malaria, herpes zoster, measles, acute respiratory infections, trauma, metabolic disorders, chemotherapy, liver and kidney disease, heavy metal poisoning (Mee's lines), etc.
TL is benign. If inherited, no current treatment is available. If partial and acquired, no treatment is needed, but if desired and there is cause, e.g. trauma, typing, that may be minimized.
For PL, the treatment depends upon the cause.
Inherited True Leukonychia (Inherited TL). Present since early childhood. The defect is in the matrix and the nail grows out white.
Acquired, partial true leukonychia (Acquired, Partial TL). The most common form. These lesions are a bit transverse. They usually result from trauma to the nail matrix causing a temporary disruption to the nail plate formation. They will grow out as the nail grows and they ultimately will be shed. New ones may form however.
Apparent (pseudo) Leukonychia (PL). The white color here comes from the nail bed. It does not grow out. The cause here was unknown.
PL caused by Superficial White Onychomycosis
PL caused by endonyx onychomycosis.
PL caused by onycholysis from psoriasis.
PL in a patient with pseudoporphyria from renal failure and Terry's nails.
PL in Muehrckes Lines
Selenium deficiency in the setting of Crohn's disease causing leukonychia [JAMA Derm 2014;150;779]
30 year old man with complete TL with onset at 12 years of age. The nails shown fit the clinical presentation of inherited TL. However, his onset was late and there was no family history. Indian J Dermatol Venereol Leprol 2012;78:107-8
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