RESUMO
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.