Multiple melanonychia striata affecting many nails – A rare phenomenon

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Melanonychia, characterized by brown-to-black discoloration of the nail plate, most commonly presents as longitudinal melanonychia (LM) due to increased melanin production or melanocytic activity. While nail matrix nevi typically involve a single or a few nails, we report a rare case of multiple melanonychia striata secondary to nail matrix nevi in a 16-year-old boy.

A 16-year-old boy presented with a 1-year history of progressive blackish discoloration affecting multiple fingernails and toenails. The pigmentation started on a single nail and gradually involved both hands and feet. There was no associated pain, itching, or preceding trauma. His medical history was unremarkable, with no history of drug intake, systemic disease, or exposure to potential triggers.

Cutaneous examination revealed multiple longitudinal black bands of varying widths on several nails, most prominently involving the thumbs, index and middle fingers, and great toes [Figures 1 and 2]. Dermoscopy showed homogeneous black longitudinal bands with parallel edges extending up to the proximal nail fold, without irregular features suggestive of malignancy [Figure 3]. Based on the clinical and dermoscopic features, a diagnosis of nail matrix nevus was made.

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Figure 1:

Longitudinal melanonychia involving multiple fingernails.

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Figure 2:

Longitudinal melanonychia involving multiple fingernails and toenails.

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Figure 3:

Dermoscopic image of the right thumbnail showing homogeneous black longitudinal bands with parallel edges extending to the proximal nail fold, without malignant features. DermLite DL4 dermatoscope in contact polarized mode with 10× magnification.

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Melanonychia striata longitudinalis denotes linear pigmentation of the nail plate that may affect one or multiple nails and vary in width and intensity. The condition results either from increased melanin production or activation of melanocytes or from an increased number of melanocytes within the matrix.^[1] Reported etiologies include benign nevi, trauma, infections, systemic diseases, medications, and – rarely – malignant melanoma, necessitating thorough evaluation.

In children, LM is most commonly associated with benign melanocytic nevi, whereas in adults, melanocytic activation predominates.^[2] As approximately two-thirds of nail melanomas initially present as LM, clinicians must maintain a high index of suspicion.^[3] Subungual melanoma, although rare (0.7–3.5% of all melanomas), may present with color variegation, irregular borders, and periungual extension of pigment (Hutchinson’s sign).^[3]

Recent studies indicate that pediatric LM can display features mimicking melanoma, such as broad or irregular bands and periungual extension; however, most cases remain benign.^[4,5] Dermoscopy combined with serial clinical monitoring is often sufficient, reducing the need for biopsy in children.^[5] In adults with acquired solitary LM demonstrating malignant features (single-digit involvement, width >6 mm, proximal widening, or ulceration), biopsy remains essential.^[1,3]

Large reviews emphasize that dermoscopy significantly improves diagnostic accuracy, helping distinguish melanocytic LM from hemorrhagic or infectious causes, while serial dermoscopic imaging is recommended for benign, multi-nail LM.^[1,5,6] These insights support a conservative, observation-based approach in children and adolescents with stable, symmetrical melanonychia.

This case highlights an unusual presentation of multiple melanonychia striata due to nail matrix nevi – a rare benign entity that underscores the importance of careful clinical and dermoscopic evaluation to differentiate it from subungual melanoma, particularly in younger patients.