Nail plate dermoscopy
Examination of the nail plate free edge permits the observation of subungual localized hyperkeratosis in epithelial tumors of the nail matrix such as Bowen disease, squamous cell carcinoma, onychopapilloma, onychomatricoma and seborrheic keratosis. In onychomatricoma, its remarkable “dotted” free edge surface constitutes another criterion in favor of this diagnosis. In onychopapilloma, the sharp “spine-shaped” hyperkeratotic plug visible underneath the nail plate in the area of nail changes is also very helpful.
It is also of interest to dermoscopically examine the distal free edge of the nail plate in cases of melanonychia striata since the position of the pigment in the nail plate gives an interesting indication of the location of the pigmented lesion with the matrix (i.e. proximal versus distal matrix). Since the dorsal aspect of the nail plate is derived from the proximal matrix, the presence of the pigment in the upper part of the nail plate free edge will indicate the site of the causal lesion in the proximal part of the matrix. In contrast, the presence of pigment in the lower part of the nail plate will favor a distal matrix location of the causative lesion. Knowing or estimating the location of a pigmented lesion preoperatively is of tremendous importance in order to inform the patient of the possible esthetic consequences of the biopsy. A biopsy taken from the distal matrix will create a nail plate with an almost invisible defect from underneath whereas a biopsy of the proximal matrix will cause a visible defect of the nail plate surface.
- 28 Braun RP, Baran R, Saurat JH, Thomas L. (2006) Surgical Pearl: dermoscopy of the free edge of the nail to determine the level of nail plate pigmentation and the location of its probable origin in the proximal or distal nail matrix. J Am Acad Dermatol 55(3): 512–13.
- 29 Jellinek N. (2007) Nail matrix biopsy of longitudinal melanonychia: diagnostic algorithm including the matrix shave biopsy. J Am Acad Dermatol 56(5): 803–10.