Perrin Christophe, Michiels Jean-F, Boyer Julien, Ambrosetti Damien
Laboratoire Central d'Anatomie Pathologique, Hôpital L. Pasteur, University of Nice, Nice, France.
Nail's Dermatology Consultations, Cannes, France.
Am J Dermatopathol. 2018 Mar;40(3):180-184. doi: 10.1097/DAD.0000000000000940.
Previous studies of the density of melanocytes in the normal nail bed have had conflicting results. This is unfortunate because knowing the normal values might help the difficult distinction between a benign subungual melanotic macule and an early melanoma in situ. Five specimens of normal nail unit were analyzed. On hematoxylin and eosin-stained sections the melanocytes were undetectable. We defined the melanocyte count (MC) as the number of melanocytes per 1-mm stretch of nail epithelium. The mean MC for nail matrix was 6.86 with a range of 4-14. The melanocytes were irregularly scattered in the basal and suprabasilar layer of the matrix epithelium. Abundant and uneven cytoplasmic dendrites were focally observed in the matrix. The MC for the nail bed ranged from 0 to 5 with a mean of 0.43. The melanocytes were restricted to the basal layer with thin cytoplasmic dendrites. Two cases showed a complete absence of melanocytes in the nail bed. In the ventral portion of the proximal nail fold, called the eponychium, the MC ranged between 0 and 5/mm with a mean of 2.27/mm. In conclusion, we discovered foci in normal nail beds, in which the melanocytic density can be relatively high and reach the level seen in the matrix. HMB45 is more sensitive than Microphtalmia-associated transcription factor (MITF) for the evaluation of intraepithelial melanocytic density of the nail unit. If MITF is used alone in the nail bed, its weak sensitivity may result in a false-negative interpretation and may be wrongly reassuring in the evaluation of early melanomas. On hematoxylin and eosin sections, basal and suprabasal nail keratinocytes are sometimes crowded, showing oval or elongated dark-staining nucleus and a clear cytoplasm and mimics a melanocytic proliferation. On HMB45 or Melan A staining, the morphology and the distribution of the dendrites of matrical melanocytes can mimic the dendritic pattern usually described in acral melanoma. Therefore, the interpretation of nail melanocytic atypia must be prudent.
以往关于正常甲床黑素细胞密度的研究结果相互矛盾。这很遗憾，因为了解正常值可能有助于区分良性甲下黑素斑和早期原位黑素瘤这一难题。对5个正常甲单位标本进行了分析。在苏木精-伊红染色切片上未检测到黑素细胞。我们将黑素细胞计数（MC）定义为每1毫米甲上皮中的黑素细胞数量。甲母质的平均MC为6.86，范围为4至14。黑素细胞不规则地散布在甲母质上皮的基底和基底上层。在甲母质中局部观察到丰富且不均匀的细胞质树突。甲床的MC范围为0至5，平均值为0.43。黑素细胞局限于具有薄细胞质树突的基底层。2例甲床完全没有黑素细胞。在近端甲褶的腹侧部分，即甲上皮，MC范围为0至5个/毫米，平均值为2.27个/毫米。总之，我们在正常甲床中发现了一些区域，其中黑素细胞密度可能相对较高，达到甲母质中的水平。HMB45比小眼畸形相关转录因子（MITF）对评估甲单位上皮内黑素细胞密度更敏感。如果仅在甲床中使用MITF，其较弱的敏感性可能导致假阴性解读，并且在评估早期黑素瘤时可能会错误地让人放心。在苏木精-伊红切片上，基底和基底上层的甲角质形成细胞有时会拥挤，显示椭圆形或细长的深色细胞核和清晰的细胞质，类似黑素细胞增殖。在HMB45或Melan A染色上，甲母质黑素细胞树突的形态和分布可模仿通常在肢端黑素瘤中描述的树突模式。因此，对甲黑素细胞异型性的解读必须谨慎。
