Practice Dilemma: Expanding Melanonychia in the Paediatric Setting

Abstract

Introduction

Differentiating between benign and malignant pathology in melanonychia can be challenging, particularly in paediatric patients as nail biopsies often require general anaesthesia.

Case Presentation

An 11-year-old healthy Vietnamese female presented with a pigmented right third fingernail. It was first noticed at age 1 and had gradually involved the whole nail plate by age 4. On examination, Hutchinson's sign was thought to be positive. Dermatoscopy revealed a variation of colours and spacing of the pigmentation. Due to the concerning clinical findings, nail removal was performed. Histology of the nail matrix squamous epithelium showed prominent melanin pigmentation. Both SOX10 and Melan A stain showed an increase in the melanocytes within the nail bed epithelium. There was no confluence of melanocytes or melanocytic nests within the nail matrix epithelium. Overall, a benign process (lentigo with melanocyte hyperplasia) was favoured given the young age of the patient, lack of cell atypia, lack of confluence or expansile growth, and a lack of significant pagetoid spread of the melanocytes.

Conclusion

Ascertaining the cause of melanoychia can be challenging, and histology may not clearly differentiate between benign and malignant causes. Careful clinical evaluation and detailed discussion with the patient and family should be thoroughly undertaken in those cases.

Established Facts

• Already known fact 1: differentiating between benign and malignant pathology of longitudinal melanonychia can be challenging, especially in the paediatric population.

• Already known fact 2: clinical signs of longitudinal melanonychia in children may be concerning even with benign pathologies.

Novel Insights

• New information 1: careful consultation should be conducted with the family with regard to the management of the longitudinal melanonychia in children.

• New information 2: the histologic confirmation of the diagnosis may be challenging even amongst experienced dermatopathologists.

Introduction/Literature Review

Longitudinal melanonychia (LM) is defined as a linear band of pigmentation affecting the nail plate, with a prevalence of 0.8% in Asians and 1.4% in Caucasians [1, 2]. LM can be caused by systemic disease, inflammatory skin conditions, drugs, or physical triggers. More importantly, it may be an early sign of subungual melanoma [3].

Subungual melanoma is extremely rare in the paediatric population. However, differentiating between benign and malignant pathology can be challenging. This is more complex in paediatric patients as nail biopsies often require general anaesthesia.

Case Report

We present the case of an 11-year-old healthy Vietnamese girl with a pigmented right middle fingernail. It was first noticed at the age of 1 year and had gradually involved the whole nail plate by age 4. There was no family history of melanoma. On examination, the entire right third fingernail was black, and Hutchinson's sign was thought to be positive (Fig. 1). Dermatoscopy revealed a variation of colours and spacing of the pigmentation (Fig. 2). She had no other concerning signs including nail dystrophy, pain, bleeding, or lymphadenopathy. Due to the irregularity of the pigmentation widths and variation of the colour, nail removal was considered after a careful discussion with the family. Excision of the entire nail bed and matrix was performed with the differential diagnosis being Spitz naevus or melanoma. Histology of the nail matrix squamous epithelium showed prominent melanin pigmentation. Both SOX10 and Melan A stain showed an increase in the melanocytes within the nail matrix epithelium. However, there was no confluence of melanocytes, which was against melanoma in situ, and there were no melanocytic nests, which was against a naevus.

Fig. 1.

Evolution of LM at 1-year-old (a) at 2-year-old (b) at 11-year-old (c).

Fig. 2.

Dermatoscopic image of nail.

Five experienced dermato-pathologists reviewed the case. Overall, a benign process (a lentigo with melanocyte hyperplasia) was favoured given the young age of the patient, lack of cell atypia, lack of confluence or expansile growth, and a lack of significant pagetoid spread of the melanocytes. The postoperative appearance was satisfactory, and it was not as noticeable as the prominent black nail (Fig. 3).

Fig. 3.

Postoperative appearances following nail excision.

Discussion/Conclusion

Clinical features which favour subungual melanoma in LM include older age, longer duration, multiple colours, larger width of pigmentation, Hutchinson's sign, and nail plate dystrophy [4, 5]. The pigmentation width of more than 28% of the whole nail is more suggestive of subungual melanoma [6]. Those features, however, could not help to reliably differentiate between benign causes and melanoma in this case.

Pham et al. [7] demonstrated that congenital nail matrix nevi tend to have worrisome signs mimicking adult subungual melanoma. In retrospect, this patient demonstrated pseudo-Hutchinson's sign rather than Hutchinson's sign because it was difficult to appreciate at the time of consultation. The histology of LM may also be challenging, as demonstrated in this case, due to prominent lentiginous growth and high-grade cytologic atypia in the paediatric group [8]. There is limited consensus on the best approach and management of LM, even more so in the paediatric population. Given the rarity of paediatric subungual melanoma, a watch-and-wait strategy is a reasonable approach when clinical features are reassuring. Careful clinical evaluation and detailed discussion with the patient and family on the risks of an invasive procedure versus a conservative approach should be thoroughly undertaken in those cases.

Statement of Ethics

Ethical approval is not required for this study in accordance with local or national guidelines. Written informed consent was obtained from the parents for the publication of the details of their medical case and any accompanying images.

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Funding Sources

The authors have no funding sources to declare.

Author Contributions

Dr. Cheng Huang drafted the main manuscript and revised the paper for submission. Dr. Peter Bullpitt provided information on the histological findings and reviewed the manuscript. Dr. Mark Nabarrro contributed to the care of the patient, provided information on the case, and reviewed the manuscript. Prof. Dedee Frances Murrell is the primary dermatologist for the patient and reviewed and revised the manuscript.

Data Availability Statement

All data generated or analysed during this study are included in this article. Further enquiries can be directed to the corresponding author.

Funding Statement

The authors have no funding sources to declare.