What is the cause and treatment of dark-colored nails in a 10-year-old child?

Dark-Colored Nail in a 10-Year-Old Child

Immediate Assessment Priority

In a 10-year-old child with dark nail discoloration, the most likely causes are benign—including fungal infection, trauma-related subungual hematoma, or bacterial infection—and melanoma is extremely rare in this age group, though it must not be missed. 1

Differential Diagnosis by Color and Pattern

Brown to Black Pigmentation (Melanonychia)

Exogenous causes (most common in children):

• Subungual hematoma from trauma presents as an irregular, oval-shaped discoloration that does not form a neat longitudinal streak and may be unnoticed if caused by repeated microtrauma 2
• Bacterial infection (Pseudomonas aeruginosa or Proteus species) produces greenish or grayish-black hue, typically confined to the lateral nail edge 2
• Fungal infection causes thickening, discoloration, and friable texture, though toenails are more commonly affected than fingernails 3, 4

Endogenous melanin production (less common):

• Longitudinal melanonychia appears as a brown-to-black streak of even width with regular borders, caused by melanocyte activation in the nail matrix 5, 2
• Almost all cases of dark nail pigmentation in pediatric patients are benign and require no treatment 1

Critical Red Flags for Malignancy (Rare but Must Exclude)

Melanoma warning signs include:

• Width greater than 5 mm 2
• Hutchinson's sign (pigmentation extending onto periungual skin) 2
• Nail dystrophy or bleeding mass 2
• Single digit involvement in absence of systemic causes 6

However, subungual melanoma is extremely rare in children 2, 1

Diagnostic Approach

Step 1: Determine Pigment Source

Examine for exogenous causes first:

• Irregular, non-streaky pattern suggests trauma or bacterial infection 2
• Greenish-gray hue indicates Pseudomonas infection 2
• History of trauma (even minor repeated microtrauma) points to subungual hematoma 2

Step 2: If Fungal Infection Suspected

Confirm diagnosis before treatment:

• Direct microscopy with potassium hydroxide (KOH) preparation and fungal culture on Sabouraud's glucose agar are essential 7
• Calcofluor white staining enhances visualization of fungal elements 7
• Do not diagnose fungal infection based on appearance alone, as 50% of nail dystrophy cases are non-fungal despite similar clinical presentation 7

Examine for concomitant infections:

• Check for tinea capitis and tinea pedis in the child 3
• Examine parents and siblings for onychomycosis and tinea pedis 3

Step 3: If Longitudinal Melanonychia Present

Dermoscopy is used routinely in evaluation of pigmented nails 6

Biopsy indications:

• Biopsy with histopathologic examination is the gold standard when melanocytic proliferation is suspected 6
• In children, given the extreme rarity of melanoma, a wait-and-see approach may be appropriate for benign-appearing lesions 5, 1

Treatment Based on Etiology

Confirmed Fungal Infection (Onychomycosis)

Topical therapy considerations:

• The nail plate in children is thin and grows faster than in adults, making topical treatment often advocated 3
• However, there are no clinical trials demonstrating efficacy of topical therapies for onychomycosis in pediatric populations 3

Systemic therapy (higher efficacy):

• Pulse itraconazole (5 mg/kg/day for 1 week every month): 2 months for fingernails, 3 months for toenails, with 94-100% clinical cure rates 3
• Daily terbinafine for 6 weeks (fingernails) or 12 weeks (toenails): 62.5 mg/day if weight <20 kg, 125 mg/day for 20-40 kg, 250 mg/day if weight >40 kg, with 88% cure rate 3, 8
• Fluconazole 3-6 mg/kg once weekly: 12-16 weeks for fingernails, 18-26 weeks for toenails 3

Azoles are advocated when onychomycosis is caused by Candida species 3

Pediatric studies demonstrate higher cure rates and faster response to treatment than in adults 3

Bacterial Infection (Green Nail Syndrome)

Treatment includes:

• Keep affected area dry 4
• Apply topical povidone iodine 2% twice daily 4

Subungual Hematoma

Conservative management:

• Observation as the hematoma will grow out with the nail 2
• No specific treatment required for benign trauma-related discoloration 5

Benign Melanonychia

Conservative approach:

• Benign lesions and hyperpigmentation may benefit from a wait-and-see approach 5
• Almost all dark nail pigmentation in children is benign and requires no treatment 1

Common Pitfalls to Avoid

• Do not assume fungal infection without laboratory confirmation, as 50% of dystrophic nails are non-fungal 7
• Do not overlook examination of family members for fungal infections, as household transmission is common 3
• Do not rush to biopsy melanonychia in children given the extreme rarity of melanoma in this age group, unless red flags are present 2, 1
• Recognize that optimal clinical effect of antifungal treatment is seen months after therapy cessation due to time required for healthy nail outgrowth 8