Reply to: “Limitations and challenges of nail unit dermoscopy in longitudinal melanonychia”

Reply to: ‘‘Limitations and challenges of nail unit dermoscopy in longitudinal melanonychia’’ To the Editor: We appreciate the interest in our study and sharing interesting cases of nail apparatus melanoma with inconspicuous dermoscopic features by Knackstedt and Jellinek.1 Histopathologic examination has been the gold standard in diagnosing malignant melanoma (MM). Investigating longitudinal melanonychia (LM) cases is no exception. Although detecting early MM by histopathologic examination is crucial, a noninvasive method should be considered as the first-line management modality in benign cases. Nail matrix biopsy should be carefully conducted unlike biopsies on the other parts of the skin where it can be easily performed for diagnostic and cosmetic purposes. Sequelae such as nail detachment or permanent onychodystrophy could occur. Furthermore, local anesthesia could result in severe pain, which could be a traumatic experience, particularly in children. In this regard, we perform nail matrix biopsy in cases with high suspicion index for malignancy. The ideal management strategy for LM is detecting MM in the early stage and observing benign lesions without invasive procedures. MM in the nail matrix is exceptionally rare in children. To our knowledge, only 13 cases have been reported in the literature, and 11 of these cases

presented as LM.2 The 11 cases presenting as LM were MM in situ. The histopathologic diagnosis is controversial in some of the cases, which meant these might not actually be MM. The histopathologic diagnosis of LM in children is difficult because melanocytes may show nuclear atypia, pagetoid distribution, and transepidermal migration of melanocytes in benign lesions.2 The biologic status of melanocytes in nail matrix nevi in children is not static. Nail matrix nevi in children can rapidly enlarge or regress during follow-up (Fig 1); it represents the underlying biologic instability of the melanocytes. In difficult melanocytic tumor cases, discordance among dermatopathologists is high, even with new molecular tests.3 The wait-and-see strategy seems appropriate for LM in children, rather than performing a histopathologic examination.4 As we mentioned in our study limitations, histopathologic examination was performed only in selected cases. The aim of our study was to compare clinical features in nail matrix nevi between adults and children.5 If we only included histopathologically confirmed cases, it would result in selection bias. We could minimize it by including clinically diagnosed cases. We completely agree that some cases of MM in the early stages could have a subtle clinical manifestation. Therefore, we performed nail matrix biopsy or recommend patients to visit the clinic every 3 to 6 months in uncertain cases.

Fig 1. Dermoscopic patterns of melanonychia in a 2-year-old boy. A, Brown-to-black band (width, 2 mm) with triangular patterns and dots/globules. B, Pigmentation broadened to 3.5 mm, with lightening of color (brown) of the band 6 months later. Hutchinson sign on the hyponychium was newly detected. J AM ACAD DERMATOL

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In our experience, dermoscopy is useful in clinically diagnosing LM and determining the necessity of nail matrix biopsy. Its usefulness has been largely investigated in the management of MM of the trunk, extremities, face, and acral skin. Although dermoscopy does not allow direct observation of nail matrix pigmentation, we could presume the underlying pathologic status by investigating morphologic manifestations of the nail plate. The validation of this tool in the management of LMs needs further studies. Jungyoon Ohn, MD,a and Je-Ho Mun, MD, PhDa,b From the Department of Dermatology, Seoul National University College of Medicine,a and Institute of Human-Environment Interface Biology, Seoul National University, Seoul, Koreab Funding sources: None. Conflicts of interest: None declared. Correspondence to: Je-Ho Mun, MD, PhD, Department of Dermatology, Seoul National University

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College of Medicine, 101 Daehangno, Chongnogu 110-744, Seoul, Korea. E-mail: [email protected]

REFERENCES 1. Knackstedt T, Jellinek NJ. Limitations and challenges of nail unit dermoscopy in longitudinal melanonychia. J Am Acad Dermatol. 2017;76:e71-e72. 2. Bonamonte D, Arpaia N, Cimmino A, et al. In situ melanoma of the nail unit presenting as a rapid growing longitudinal melanonychia in a 9-year-old white boy. Dermatol Surg. 2014;40:1154-1157. 3. Bitterman A. Molecular testing to differentiate melanoma from benign nevi: the gold standard limitation. J Am Acad Dermatol. 2016;75:849-850. 4. Koga H, Yoshikawa S, Shinohara T, et al. Long-term follow-up of longitudinal melanonychia in children and adolescents using an objective discrimination index. Acta Derm Venereol. 2016;96:716-717. 5. 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. http://dx.doi.org/10.1016/j.jaad.2016.10.021