What is the best course of action for a 9-year-old patient with a two-month history of a brown melanocytic asymmetric patch under their toenail?

Urgent Dermatology Referral for Nail Matrix Biopsy

This 9-year-old requires immediate referral to a dermatologist with expertise in nail apparatus biopsy to rule out subungual melanoma, which cannot be missed despite being rare in children. 1, 2

Why This Requires Urgent Action

The asymmetric brown melanocytic patch under the toenail is a red flag that demands expert evaluation, even in a child. While melanoma is uncommon in pediatric patients, the consequences of delayed diagnosis are severe—subungual melanoma has a mean diagnostic delay of 2 years and only 43% 10-year survival. 2 The American Academy of Dermatology emphasizes that the primary concern when evaluating brown nail pigmentation is ruling out nail unit melanoma, which requires nail matrix biopsy by a practitioner skilled in nail apparatus procedures. 1

Clinical Features That Raise Concern

This lesion demonstrates concerning characteristics that warrant urgent evaluation:

• Asymmetry is explicitly mentioned, which is a worrisome feature for malignancy 1, 2
• Single digit involvement rather than multiple nails increases suspicion for pathologic process 2, 3
• Two-month duration represents a relatively recent change that requires documentation and expert assessment 4

The American Academy of Dermatology specifies that urgent biopsy is indicated when melanonychia demonstrates irregular borders or color variation, progressive change, or associated nail plate damage. 2

Why Not "Wait and See" in This Case

While benign melanocytic hyperplasia (lentigo or nevus) accounts for 77.5% of longitudinal melanonychia cases in pediatric populations 5, and many experts advocate a conservative "wait-and-see" approach for children 3, 5, the described asymmetry changes the risk calculus. The American Academy of Dermatology explicitly warns against delaying referral for "watchful waiting" in cases with suspicious features, as delaying biopsy can impact survival outcomes. 2

Critical Pitfalls to Avoid

• Never perform superficial sampling or shave biopsy if melanoma is suspected, as this may underestimate depth and stage 2
• Do not assume fungal infection without mycological confirmation—50% of dystrophic nails are non-fungal, and the American Academy of Dermatology warns against diagnosing based on appearance alone 1
• Do not treat empirically with antifungals before establishing a diagnosis, particularly in single-nail involvement 2
• Do not delay referral based on the patient's young age—benign pediatric longitudinal melanonychia may exhibit clinical features resembling adult melanoma 4

What the Specialist Will Do

The dermatologist will perform:

• Complete skin examination to assess for other pigmented lesions and risk factors 2
• Dermoscopy of the nail lesion with clinical photography for documentation 2, 4
• Nail matrix biopsy if indicated—the gold standard for diagnosing or ruling out nail unit melanoma 4
• Tangential excisional biopsy is recommended for suspicious lesions, while longitudinal excision is reserved for high-likelihood invasive melanoma 4

The specialist may also obtain nail clippings for histopathologic examination, which can be a useful initial diagnostic tool to avoid biopsy or aid in biopsy planning. 4

Alternative Diagnoses to Consider

While melanoma must be excluded first, other possibilities include:

• Melanocytic nevus (junctional or compound)—the most common cause of melanocytic hyperplasia in children, accounting for 47.5% of cases in one pediatric series 5
• Lentigo—accounting for 30% of pediatric melanonychia cases 5
• Melanocytic activation without hyperplasia—seen in 22.5% of pediatric cases 5
• Onychomycosis—requires KOH preparation and fungal culture for confirmation 1
• Chronic trauma—can cause nail discoloration and dystrophy 2

However, these diagnoses can only be entertained after malignancy is excluded by expert evaluation. 1, 2