What is the role of dermatoscopy in the workup of melanonychia?

Updated: Sep 10, 2018
  • Author: Chris G Adigun, MD, FAAD; Chief Editor: William D James, MD  more...
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Examination of affected nails with a dermatoscope can provide useful information regarding both the etiology and location of longitudinal melanonychia. [26] Considering the dermatoscopic appearance of subungual nevi and subungual melanoma, nevi have been reported to demonstrate regular parallel lines, while subungual melanoma has been reported to demonstrate irregular lines with some disruption of parallelism.

In an effort to differentiate neoplastic from reactive processes of the nail apparatus, additional dermoscopic features have been described by Ronger et al and Braun et al. [25, 26, 27] These features include blood spots, brown coloration of the background, grayish background and thin gray lines, micro-Hutchinson sign, and microscopic grooves. Of these dermoscopic patterns, the features that most commonly occur with melanoma include a brown background hue, the presence of irregular longitudinal lines, and the presence a micro-Hutchinson sign. The micro-Hutchinson sign has been described as pigmentation of the cuticle that is only appreciable with use of a dermatoscope. [26] The diagnostic algorithms described by Ronger et al and Braun et al describe 2 forms of pigment: grayish color and brownish color. Grayish color suggests focal melanocyte activation in the absence of melanocytic hyperplasia. Brownish color suggests melanocytic hyperplasia.

These dermoscopic criteria may be applied in the decision about whether to perform a biopsy and the location of the biopsy. Adigun et al suggest biopsy should be performed when longitudinal melanonychia reveals irregular lines or the micro-Hutchinson sign. [28] If dermoscopic evaluation reveals a reassuring regular pattern of parallel lines, the decision to observe every 6 months may be sufficient.

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