Nail disorders in children — formative SAQs

SAQ 1 (10 marks)

A 9-year-old boy is referred with an 18-month history of a progressively thickened, yellow, crumbly left great toenail. His father has tinea pedis and a thickened toenail. The nail shows subungual hyperkeratosis and distal onycholysis. No mycology has been done. The family asks for tablets to clear it. ^[4]

Question: (a) What is the likely diagnosis, and what must you do to confirm it before any systemic treatment, and why? (b) Outline the stepwise management once confirmed, including a specific drug, dose and duration. (c) What else should you address, and what are the red flags in a child with a disordered nail? (10 marks) ^[1]

Model answer

(a) Diagnosis and confirmation (3 marks). The likely diagnosis is onychomycosis — a thickened, discoloured, crumbly nail with subungual hyperkeratosis and distal onycholysis, in a child with a household contact (his father), which is a recognised transmission risk. Before any systemic treatment, confirm with mycology: take subungual debris from the most proximal active edge for potassium hydroxide examination plus fungal culture, or polymerase chain reaction where available. The reason is practical and safety-driven — the clinical appearance overlaps with psoriasis and trauma, and systemic antifungals carry hepatic and drug-interaction risk, so a child should not receive them on appearance alone. ^{[4] [1]}

(b) Stepwise management (4 marks). Once confirmed, the ladder runs from topical to systemic. For limited distal disease, a topical agent such as amorolfine or efinaconazole applied over many months may suffice. For extensive disease like this (a whole great toenail over 18 months), first-line systemic therapy for dermatophyte infection is weight-based oral terbinafine: under 20 kg at 62.5 mg once daily, 20 to 40 kg at 125 mg once daily, and over 40 kg at 250 mg once daily, given for about 12 weeks for a toenail, with liver-function monitoring. Itraconazole is a specialist alternative. Set the family's expectation that a normal-looking toenail is 12 to 18 months away because of the slow growth rate, and treat the father's tinea pedis to reduce reinfection. ^{[4] [3]}

(c) Associated measures and red flags (3 marks). Address the household transmission by treating affected contacts, reinforce footwear hygiene, and explain the long regrowth time to support adherence. The red flags that must not be missed in any child with a disordered nail are a progressive, widening or darkening longitudinal melanonychia in a single nail of a fair-skinned child (possible nail melanoma), a destructive subungual lesion with bone involvement (possible exostosis or malignancy), and scarring nail lichen planus with a pterygium that threatens permanent matrix loss. If mycology is negative, reconsider nail psoriasis and trauma rather than escalating empirically. ^{[1] [7] [5]}