Dark-Colored Nail in a Child

Diagnostic Approach

Fungal infection causes thickening, discoloration, and friable texture, and the British Journal of Dermatology recommends checking for concomitant infections such as tinea capitis and tinea pedis in the child, as well as examining parents and siblings for onychomycosis and tinea pedis 1
Direct microscopy with potassium hydroxide (KOH) preparation and fungal culture on Sabouraud's glucose agar are essential for confirming diagnosis of fungal infection, according to Praxis Medical Insights 2
Calcofluor white staining enhances visualization of fungal elements, and it is important not to diagnose fungal infection based on appearance alone, as 50% of nail dystrophy cases are non-fungal despite similar clinical presentation 2

The British Journal of Dermatology recommends pulse itraconazole (5 mg/kg/day for 1 week every month) for 2 months for fingernails, 3 months for toenails, with 94-100% clinical cure rates for confirmed fungal infection 1
Daily terbinafine for 6 weeks (fingernails) or 12 weeks (toenails) is also recommended, with 88% cure rate, and the dosage is based on weight: 62.5 mg/day if weight <20 kg, 125 mg/day for 20-40 kg, 250 mg/day if weight >40 kg 1
Azoles are advocated when onychomycosis is caused by Candida species, and pediatric studies demonstrate higher cure rates and faster response to treatment than in adults 1

The British Journal of Dermatology warns against assuming fungal infection without laboratory confirmation, as 50% of dystrophic nails are non-fungal 1
Praxis Medical Insights advises against overlooking examination of family members for fungal infections, as household transmission is common 2
It is also important to keep the affected area dry and apply topical povidone iodine 2% twice daily for bacterial infection, according to Praxis Medical Insights 3

The British Journal of Dermatology recommends considering bacterial infection, such as Green Nail Syndrome caused by Pseudomonas aeruginosa or Proteus species, which requires keeping the area dry with topical povidone iodine 2% twice daily, and also considering non-infectious causes like psoriasis, lichen planus, trauma, and yellow nail syndrome, as these can mimic fungal infection but the nail surface typically doesn't become soft and friable 4
The British Journal of Dermatology suggests that bacterial infection, such as Green Nail Syndrome, and non-infectious causes should be ruled out, as these can present with similar symptoms to fungal infection, and require different management approaches 4

The British Journal of Dermatology recommends always obtaining mycological confirmation before initiating treatment, as 50% of dystrophic nails in children are non-fungal despite similar clinical appearance 5

Distal and lateral subungual onychomycosis is the most common presentation in pediatric patients, with T. rubrum being the most prevalent causative organism (64% of cases), followed by T. tonsurans 5, 6
Superficial white onychomycosis appears as white lesions on the nail surface, particularly toenails, gradually spreading until the entire nail plate is involved, and is most commonly seen in children, usually caused by T. interdigitale 7
Onychomycosis in children often occurs with occlusive footwear and represents 15% of all nail dystrophies in this age group 5, 6

The British Journal of Dermatology recommends terbinafine as the preferred first-line treatment for dermatophyte onychomycosis in children, with superior efficacy over other agents 8
Terbinafine dosing is weight-based: <20 kg, 62.5 mg daily; 20-40 kg, 125 mg daily; >40 kg, 250 mg daily, with treatment duration of 6 weeks for fingernails and 12 weeks for toenails 8
Itraconazole pulse therapy is equally effective as first-line treatment, particularly useful when Candida species are suspected, with dosing of 5 mg/kg/day for 1 week per month, and treatment duration of 2 pulses (2 months total) for fingernails and 3 pulses (3 months total) for toenails 8
Fluconazole can be used as a second-line option, with dosing of 3-6 mg/kg once weekly, and treatment duration of 12-16 weeks for fingernails and 18-26 weeks for toenails 8
Griseofulvin can be used as a second-line option, with dosing of 10 mg/kg/day, and treatment duration of at least 4 months for fingernails and at least 6 months for toenails 8

Baseline liver function tests and complete blood count are recommended for patients on terbinafine, and monitoring of liver function tests is recommended for patients on itraconazole, particularly those with pre-existing abnormalities or receiving continuous therapy >1 month 8
Preventive measures include applying regular antifungal powder inside shoes and periodic terbinafine solution spraying into shoes, as well as daily topical emollients to cuticles and periungual tissues 8

In patients with nail discoloration, fungal infections can produce nail‑plate thickening, yellow‑brown discoloration, and a friable texture, which differentiates them from true melanin‑derived melanonychia. 9

In individuals with nail changes, lichen planus may cause nail‑plate thinning, longitudinal ridging, and occasional pigmentation. 9