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Updated: May 29, 2026

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Published on: February 28, 2025
The histopathological feature of the nail isthmus in an ectopic nail
Naoki Oiso1, Ichiro Kurokawa, Daisuke Tsuruta
1Department of Dermatology, Kinki University Faculty of Medicine, Osaka, Japan. naoiso@med.kindai.ac.jp
Abstract:
The nail unit has a unique structure. It has been recently proposed that the nail isthmus as a transitional zone between the most distal part of the nail bed and the hyponychium. A 7-year-old Japanese boy presented with an ectopic nail, an additional and independent miniature nail on the digital pulp of the right fifth finger. We studied the expression of a series of keratin in longitudinal specimens and showed the histopathological manifestation in the nail isthmus. This region in the ectopic nail is subdivided into 2 parts: a proximal and narrow part anchored to the nail plate and a distal and wide part with a semihard keratinized structure.
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