Limitations and challenges of nail unit dermoscopy in longitudinal melanonychia

Limitations and challenges of nail unit dermoscopy in longitudinal melanonychia To the Editor: We read with interest the article by Ohn et al1 on dermoscopic features of nail matrix nevi (NMN) in adults and children. We agree that establishing the nature of adult and pediatric longitudinal melanonychia can be challenging. Dermoscopy may be a useful adjunct in some cases. However, unlike in the skin, nail plate dermoscopy does not permit analysis of the pigment origin in the nail matrix epithelium. In this regard, we would like to issue a word of caution. We have treated biopsyproven pediatric nail apparatus melanoma in situ (NAMis) and adult NAMis with notably inconspicuous dermoscopic features (which, taken alone, may have been inappropriately reassuring). Features discussed by Ohn et al1 such as triangular sign, Hutchinson sign, nail dystrophy, subungual hemorrhage, and dermoscopic dots and globules may be more pronounced in pediatric versus adult NMN but do not reliably differentiate between the more clinically significant distinction of benign versus malignant. Our pediatric patients presented with longitudinal melanonychia with a mean 4-mm width (and 1 complete melanonychia), with parallel brown lines, at times with homogeneous darker browns streak centrally (Fig 1). Among adults, many cases demonstrated relatively uniform clinical and dermoscopic findings (Fig 2). Indeed, brown lines arising on a lighter brown background with relatively inconspicuous irregularity were seen in our NAMis cases and are reported by others.2 In addition to the somewhat nonspecific dermoscopy findings in pediatric and adult NAMis demonstrated herein, we would like to express concern regarding the diagnosis of NMN in adults. We believe this diagnosis cannot be reliably established merely by clinical examination and dermoscopy. Biopsy and histologic assessment remain the gold standard. Tosti et al3 reported 11 biopsy-proven adult nevi among 100 biopsied longitudinal melanonychia cases. Many of these cases and those published in the literature had a congenital or childhood/adolescent onset. In the absence of such a long natural history, biopsy is essential. We advocate using the tangential matrix shave to establish the diagnosis and minimize risks of nail dystrophy.4 With appropriate local anesthesia this technique is well tolerated in adults and older children. When demonstrating the validity of dermoscopy, it is important to validate the tool in relation to the J AM ACAD DERMATOL

Fig 1. Dermoscopy of nail apparatus melanoma in situ (NAMis) of the left great toe in a 9-year-old boy showing light-brown longitudinal pigmentation with central darker brown yet regular streak. Inset: Clinical appearance of biopsy-proven NAMis with 3.5-mm wide light-brown longitudinal melanonychia with subtle pigmentation of the lateral nailfold.

established gold standard, histology. This approach was not the norm in the study by Ohn and colleagues1 and biopsy was only performed in 12.9% of the cases. Adult NAMis can be deceivingly subtle with a banal clinical presentation.5 Adult NAMis can be indolent and mean reported followup of 15 months1 may not be enough to

Fig 2. Dermoscopy of nail apparatus melanoma in situ (NAMis) of the left fourth finger (ring finger) in a 25year-old woman showing regular medium-brown lines with distal splinter hemorrhage. Inset: Clinical appearance of biopsy-proven NAMis with a 4-mm wide medium-brown longitudinal melanonychia without proximal nailfold pigmentation.

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demonstrate the evolving natural history of what may be NAMis rather than adult NMN. Indeed, in our clinic, the average lag time from lesion onset to establishing a diagnosis of NAMis is 4.8 years (unpublished data). In conclusion, dermoscopy certainly has its merits but at this point is best used either as a limited adjunct to the clinical examination (without replacing biopsy for establishing a diagnosis), or in the form of intraoperative dermoscopy at the time of a definitive diagnostic procedure, where it may guide operative margins. Thomas Knackstedt, MD,a,d and Nathaniel J. Jellinek, MDa,b,c Dermatology Professionals Inc, East Greenwich, Rhode Islanda; Department of Dermatology, Warren Alpert Medical School of Brown University, Providence, Rhode Islandb; Division of Dermatology, University of Massachusetts Medical School, Worcesterc; and Department of Dermatology, Cleveland Clinic Foundation, Ohiod

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Funding sources: None. Conflicts of interest: None declared. Correspondence to: Nathaniel J. Jellinek, MD, Dermatology Professionals Inc, 1672 S County Trail, Suite 101, East Greenwich, RI 02818. E-mail: [email protected]

REFERENCES 1. Ohn J, Choe YS, Mun JH. Dermoscopic features of nail matrix nevus (NMN) in adults and children: a comparative analysis. J Am Acad Dermatol. 2016;75:535-540. 2. Ronger S, Touzet S, Ligeron C, et al. Dermoscopic examination of nail pigmentation. Arch Dermatol. 2002;138:1327-1333. 3. Tosti A, Baran R, Piraccini BM, Cameli N, Fanti PA. Nail matrix nevi: a clinical and histopathologic study of twenty-two patients. J Am Acad Dermatol. 1996;34:765-771. 4. Jellinek N. Nail matrix biopsy of longitudinal melanonychia: diagnostic algorithm including the matrix shave biopsy. J Am Acad Dermatol. 2007;56:803-810. 5. Jellinek NJ. Dermoscopy between the lines. Arch Dermatol. 2010;146:431-433. http://dx.doi.org/10.1016/j.jaad.2016.09.049