Nail disorders in children — branching viva

Opening question

Examiner: Take me through this child. What is the likely diagnosis, and what is your frame for assessing a disordered nail? [1]

Candidate: The likely diagnosis is onychomycosis — a thickened, discoloured, crumbly toenail with subungual hyperkeratosis and distal onycholysis, in a child with a household contact, which is a recognised transmission route. My frame for any disordered nail rests on one principle: localise the lesion to the part of the nail unit it arises from. The matrix makes the plate, so matrix disease shows as surface and shape change; the nail bed sits under the plate, so bed disease shows as colour and attachment change; the nail fold surrounds the nail, so fold disease shows as swelling and pus. This child's signs are bed and plate changes — thickening, hyperkeratosis and onycholysis — consistent with fungal invasion of the bed and the underside of the plate. [1] [4]

Examiner: Walk me through the nail unit anatomy and the growth rate, and why it matters. [1]

Candidate: The nail matrix is the germinative epithelium tucked under the proximal nail fold that generates the nail plate; its distal edge shows as the pale lunula. The nail plate is the hard keratin nail, riding forward over the tightly adherent nail bed. The proximal and lateral nail folds frame the nail, and the cuticle or eponychium seals the gap and protects the matrix. The hyponychium is where the plate finally separates from the bed at the tip. Fingernails grow about 3 mm a month and take roughly 6 months to regrow, while toenails take 12 to 18 months — which matters because a brief halt in matrix activity after an illness leaves a Beau line that crawls distally over months, and because a treated toenail takes a year or more to look normal. [1]

Branch 1 — confirming and treating onychomycosis

Examiner: What will you do before treating this nail, and why? [4]

Candidate: I will confirm with mycology before any systemic therapy: take subungual debris from the most proximal active edge for potassium hydroxide examination plus fungal culture, or polymerase chain reaction. The reason is that the clinical appearance of onychomycosis overlaps with psoriasis and trauma, and systemic antifungals carry hepatic and drug-interaction risk, so a child should not receive them on appearance alone. Onychomycosis is also far less common in children than adults, which is exactly why confirmation matters before reaching for a tablet. [4] [1]

Examiner: It is confirmed as a dermatophyte. How will you treat? [4]

Candidate: For limited distal disease I would use a topical agent such as amorolfine or efinaconazole over many months. For extensive disease like this, first-line 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, for about 12 weeks for a toenail, with liver-function monitoring. Itraconazole is a specialist alternative. I would treat his father's tinea pedis to reduce reinfection and set the expectation that a normal toenail is 12 to 18 months away. [4] [3]

Branch 2 — the inflammatory and traumatic nails

Examiner: If the mycology were negative, what else would you consider? [1]

Candidate: I would reconsider nail psoriasis — which gives onycholysis with the oil-drop or salmon-patch discolouration and pitting, in a child with psoriasis elsewhere, and is mycology negative — and trauma, including repetitive shoe trauma. If several nails were thin, rough and sandpaper-like rather than thickened, that would be trachyonychia or twenty-nail dystrophy, which may be idiopathic or secondary to lichen planus, psoriasis or alopecia areata, so I would examine the skin, scalp and hair. [1] [5]

Examiner: How do you manage trachyonychia, and what is the emergency among the inflammatory nails? [5]

Candidate: Idiopathic trachyonychia in a child often improves or resolves over months to years, so I reassure, protect the nails, and stop biting. I use a potent topical corticosteroid to the proximal nail fold and matrix for symptomatic inflammatory disease. The emergency is scarring nail lichen planus — progressive thinning and dystrophy with a forward-growing pterygium — because it destroys the matrix and risks permanent nail loss, so it needs prompt potent topical or intralesional steroid to the matrix. [5] [1]

Branch 3 — the pigmented nail and the genodermatoses

Examiner: Suppose this child had a brown vertical band on one fingernail instead. How would you approach it? [7]

Candidate: That is longitudinal melanonychia — melanin in the nail plate — and in a child the commonest cause by far is a benign nail matrix naevus, often stable from early life with surrounding periungual pigment. I would characterise it with nail dermoscopy — a regular brown background with regular lines favours a naevus — and document and photograph it for serial observation, because change over time is the key discriminator. Nail melanoma is rare in children, but a single progressively widening, darkening band, especially in a fair-skinned child, is the red flag that demands specialist assessment and possible biopsy. [7] [1]

Examiner: What about a child with gross nail thickening from birth? [9]

Candidate: That raises a genodermatosis. Pachyonychia congenita presents with gross nail thickening — subungual hyperkeratosis lifting and distorting the plate — alongside painful palmoplantar keratoderma, from keratin mutations such as KRT6A or KRT16. Nail-patella syndrome gives hypoplastic or absent thumbnails with absent patellae, iliac horns and nephropathy, and is autosomal dominant (LMX1B). I would refer to dermatology and clinical genetics, screen for the associated features, and involve the family in a multidisciplinary plan. [9] [1]

Branch 4 — infections and trauma

Examiner: How do acute paronychia and the ingrown toenail differ in management? [3]

Candidate: They differ because they are different problems. Acute paronychia is a staphylococcal infection of a finger nail fold — the key step is draining a pointing abscess with a small nick, with an anti-staphylococcal beta-lactam such as flucloxacillin or cephalexin added if spreading. The ingrown toenail is a mechanical problem of a great toe — the nail edge digging into the lateral fold — so it is managed conservatively first with soaks, square trimming, and a cotton-wisp or tape to lift the edge, with antibiotics reserved for spreading infection and wedge excision with phenol matrixectomy for recurrent disease. Herpetic whitlow is the mimic to remember, giving grouped vesicles and managed with antivirals rather than antibiotics. [3] [1]

Examiner: A child catches a finger in a door with a tense bloody nail. What do you do? [1]

Candidate: A tense subungual haematoma from a recent crush needs trephination — a small hole through the nail to release the blood — ideally within hours while the clot is still liquid, for immediate pain relief. If there is a nail bed laceration with significant bleeding, I repair it with fine absorbable sutures to restore alignment and prevent permanent dystrophy, replace the nail plate as a splint, and protect the finger. These are time-sensitive steps that protect the matrix. [1]

Wrap

Examiner: Summarise your approach to paediatric nail disorders in one sentence. [1]

Candidate: Localise the lesion to the part of the nail unit — matrix for shape and surface, bed for colour and attachment, fold for swelling and pus — confirm onychomycosis with mycology before any systemic therapy and treat with weight-based terbinafine, manage the ingrown toenail conservatively first and drain paronychia, reassure around benign variants like idiopathic trachyonychia and physiological koilonychia, and never let a changing or destructive nail lesion wait, because the red flags — a changing melanonychia, a destructive subungual lesion, and scarring lichen planus — are what a paediatric nail exam exists to catch. [1] [7] [5]