Nail Punctate Leukonychia

Punctate leukonychia is characterized by white spots 1–3 mm in diameter occurring singly or in groups almost exclusively on finger nails. They are usually due to repeated minor trauma to the matrix. The evolution of the spots is variable; appearing generally on contact with the cuticle, they grow distally with the nail. Approximately half of them disappear as they migrate towards the free edge. This is believed to prove that parakeratotic cells are capable of maturing and losing their keratohyalin granules to produce keratin, even though they have been without a blood supply for many months. Some white spots enlarge, while others appear at a distance from the lunula, suggesting that the nail bed is participating by incorporating groups of nucleated cells into the nail. A similar process could explain the exclusively distal leukonychia which is occasionally seen. A local or general fault in keratinization is not the only cause of punctate leukonychia; infiltration of air, which is known to occur in cutaneous parakeratoses, was for a long time believed to play a part. Disturbance of the nail plate’s highly organized keratin fibre system alters its transparency and makes it look white. This is evidenced by polarization microscopy, as most clinically white spots lose their birefringence.

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