What could cause a dark-colored nail in an 11-year-old and how is it treated?

Dark-Colored Nail in an 11-Year-Old Child

Do not assume fungal infection based on appearance alone—50% of dystrophic nails are non-fungal, and laboratory confirmation with KOH preparation and fungal culture is essential before initiating treatment. 1

Immediate Diagnostic Priorities

The most critical first step is distinguishing between benign causes and serious conditions like subungual melanoma, though melanoma is extremely rare in children. 2 The diagnostic approach must systematically rule out:

Infectious Causes (Most Common in Children)

• Fungal infection (onychomycosis) presents with thickening, discoloration, and friable texture of the nail, and you must examine the child for concomitant tinea capitis and tinea pedis, as well as checking parents and siblings for onychomycosis and tinea pedis since household transmission is common. 1

• Superficial White Onychomycosis (SWO) is particularly common in children, presenting as crumbling white lesions on the nail surface, usually caused by T. interdigitale. 3

• Bacterial infection (Green Nail Syndrome) from Pseudomonas aeruginosa or Proteus species causes greenish or grayish discoloration, typically confined to the lateral nail edge, and requires keeping the area dry with topical povidone iodine 2% twice daily. 4, 5

Non-Infectious Causes to Rule Out

• Subungual hematoma from single heavy trauma or repeated microtrauma (often unnoticed) appears oval-shaped but doesn't form a neat streak, commonly found on the medial aspect of the great toe. 2

• Psoriasis, lichen planus, trauma, and yellow nail syndrome must be excluded, as these can mimic fungal infection but the nail surface typically doesn't become soft and friable. 4, 3

Melanocytic Lesions (Rare but Critical)

• Longitudinal melanonychia (brown-to-black pigmented streak) requires careful evaluation, though subungual melanomas are very rare in children. 2, 6

• Dermoscopy should be used routinely when evaluating pigmented nails, and biopsy with histopathologic examination is the gold standard when melanocytic proliferation is suspected. 7

• Malignant features include width >5 mm, Hutchinson's sign (pigment extending to periungual skin), nail dystrophy, and bleeding mass—though these are exceptionally uncommon in pediatric patients. 2

Required Laboratory Workup

Before treating, you must obtain:

• Direct microscopy with potassium hydroxide (KOH) preparation to visualize fungal elements. 1

• Fungal culture on Sabouraud's glucose agar for definitive identification. 1

• Calcofluor white staining to enhance visualization of fungal elements. 1

• Nail specimens should be taken from discolored, dystrophic, or brittle parts, cutting the affected nail as far back as possible through the entire thickness, including any crumbly material. 3

Treatment Algorithm Based on Confirmed Diagnosis

If Fungal Infection is Confirmed:

For fingernails:

• Pulse itraconazole 5 mg/kg/day for 1 week every month for 2 months achieves 94-100% clinical cure rates. 1
• Alternative: Daily terbinafine for 6 weeks (dosage: 62.5 mg/day if <20 kg, 125 mg/day for 20-40 kg, 250 mg/day if >40 kg) with 88% cure rate. 1

For toenails:

• Pulse itraconazole 5 mg/kg/day for 1 week every month for 3 months. 1

• Alternative: Daily terbinafine for 12 weeks. 1

• Azoles are specifically advocated when onychomycosis is caused by Candida species. 1

• Pediatric studies demonstrate higher cure rates and faster response to treatment than in adults. 1

If Bacterial Infection (Pseudomonas):

• Keep the affected area dry and apply topical povidone iodine 2% twice daily. 5

If Subungual Hematoma:

• Conservative management with observation, as the discoloration will grow out with the nail over several months. 2

If Melanocytic Lesion is Suspected:

• Refer immediately to dermatology for dermoscopy and potential biopsy, though malignancy is exceedingly rare in this age group. 7

Critical Pitfalls to Avoid

• Never diagnose fungal infection based on clinical appearance alone—this leads to unnecessary antifungal treatment in 50% of cases where the nail dystrophy is non-fungal. 1

• Don't overlook family examination—household transmission of fungal infections is common, and treating the child alone without addressing infected family members leads to reinfection. 1

• Don't miss melanoma due to age bias—while extremely rare in children, diagnostic delays average 2 years and contribute to poor prognosis when melanoma does occur. 8, 6

• Avoid assuming all dark nails are fungal—bacterial infections, trauma, and inflammatory conditions require different management approaches. 4