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CORRESPONDENCE |
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| Year : 2012 | Volume
: 57
| Issue : 5 | Page : 414-415 |
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| On the patterns of distribution of segmental nevi of melanocytic origin |
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Daniele Torchia
Via della Scala 58, 50123 Florence, Italy
| Date of Web Publication | 3-Sep-2012 |
Correspondence Address:
Daniele Torchia
Via della Scala 58, 50123 Florence
Italy
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0019-5154.100515
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How to cite this article:
Torchia D. On the patterns of distribution of segmental nevi of melanocytic origin. Indian J Dermatol 2012;57:414-5 |
Sir,
Sarma recently attempted to demonstrate that several types of pigmentary nevi of the face follow a distribution along Blaschko lines. [1] Actually, most nevi taken into consideration for the study (hypopigmented nevus, hyperpigmented nevus, segmental lentiginosis) are known to follow, when large enough, the checkerboard/block-like pattern of cutaneous mosaicism. Since no specific nevus is known to feature more than one pattern (e.g. nevus sebaceus follows only Blashko lines; large nevus spilus only presents in a checkerboard/block-like fashion, etc.) and since nevi presenting with a given pattern do so regardless of their body localization, it is very likely that the distribution pattern displayed in Sarma's study is, in fact, the block-like one. Such pattern may not be readily recognized on the face because of the smaller size and more complex anatomic/embryologic characteristics of that district with respect to other body portions. Nonetheless, when nevi of melanocytic origin are large enough, they appear on the face as roughly quadrangular/angulated patches or broad bands, similarly to what happens with block-like nevi on other extremities such as the limbs. These considerations may account for the "noticeable differences" between Blashko lines and the "patterned lines of the pigmentary nevi", as already acknowledged by Sarma. [1]
Segmental nevi originating from melanocytes do not follow Blashko lines, the only exception seemingly being the recently identified nevus lentiginosus linearis. [2],[3] Of course other pigmentary lesions are also Blashkolinear (e.g. incontinentia pigmenti, Blashkolinear hypo- and hypermelanosis) but in such an instance the mosaic genetic defect is not harbored within melanocytes. [4]
The identification of the genetic defect accounting for each nevus type may shed some light on the view that most, if not all, phenotypic patterns of cutaneous mosaicism are nevus- and cell-specific. [4]
 References | |  |
| 1. | Sarma N. Pigmentary nevi on face have unique patterns and implications: The concept of Blaschko's lines for pigmentary nevi. Indian J Dermatol 2012;57:30-4. 
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| 2. | Happle R, Metze D, Vera Casaño A. Naevus lentiginosus linearis: A distinct skin disorder. Acta Derm Venereol 2010;90:210-1.
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| 3. | Torchia D. More on "naevus lentiginosus linearis". Acta Derm Venereol 2011;91:209; author reply 209.
[PUBMED] |
| 4. | Torchia D. Mosaic pigmentation disorders and associated syndromes. J Dermatol 2012;39:414-5.
[PUBMED] |
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