Atopic dermatitis and the atopic march — short-answer questions

This stem concerns a classic infantile atopic dermatitis presentation in a child with a strong atopic family history, illustrating diagnostic criteria, barrier-and-immune pathophysiology, stepwise management, and the atopic march. [1]

Question 1 (10 marks)

a) Give the most likely diagnosis, apply the UK Working Party diagnostic criteria to this child, and outline the barrier-and-Th2 pathophysiology. (6 marks) [1]

The most likely diagnosis is atopic dermatitis of infancy. The UK Working Party criteria require an itchy skin condition plus at least three of five supporting features, and this child meets all of them: he has an intensely itchy rash (rubbing, scratching and sleep disturbance); the distribution involves the typical infantile sites of cheeks, scalp and extensor surfaces; the onset was before two years of age; he has a strong family history of atopy (maternal asthma, paternal childhood eczema); and he has generally dry skin. The sparing of the nappy area is characteristic and supports the diagnosis. [1]

The pathophysiology rests on two reinforcing pillars. The first is a defective epidermal barrier, classically from loss-of-function variants in the filaggrin gene, which reduce natural moisturising factor and ceramides, raise transepidermal water loss, and produce a dry cracked skin surface that admits antigens and supports Staphylococcus aureus colonisation. The second is a Th2-skewed immune response: antigens breaching the barrier are taken up by Langerhans cells, presented to naïve T cells that polarise toward Th2, and the resulting interleukin-4, interleukin-13 and interleukin-31 drive immunoglobulin class-switching to IgE, recruit eosinophils, and — through interleukin-31 — directly stimulate itch. The itch-scratch cycle that follows further damages the barrier and sustains chronic relapsing disease. [3]

b) Describe four characteristic clinical features and state how you would grade severity. (4 marks) [1]

The four characteristic features are the age-typical infantile distribution on cheeks, scalp and extensors with sparing of the nappy area, the intensely itchy and excoriated erythematous crusted plaques, the generally dry skin (xerosis), and the nocturnal itch disrupting sleep. The strong bilateral parental atopic history is a further supporting feature. [1]

Severity is graded with a validated instrument such as SCORAD (which combines body-surface-area extent, six clinical signs and subjective itch-and-sleep scores), EASI (a physician-assessed area-and-severity index), or POEM (a parent-completed seven-item score), with the Children's Dermatology Life Quality Index capturing quality-of-life impact. Because this child's itch disrupts sleep, the disease is at least moderate, and a SCORAD or POEM should be recorded at baseline and at each review to guide step-up and step-down of therapy. [1]

Question 2 (10 marks)

a) Outline your stepwise management according to the topical-therapy ladder and explain how you would address steroid phobia. (6 marks) [6]

Management begins with the foundation that every child needs: a generous, greasy, fragrance-free emollient applied at least twice daily, a soap-free wash, trigger avoidance advice, and a written eczema action plan that empowers the parents to step up at the first sign of a flare. This foundation alone improves control in many children and is the indispensable base of every regimen. [6]

For the active eczema on this child's cheeks and extensor forearms, a low-potency topical corticosteroid such as hydrocortisone 1% is appropriate for the face and a moderate-potency agent such as triamcinolone for the extensor limbs, applied once or twice daily for a defined course of one to two weeks until the flare settles, then stepped down. A non-steroid alternative such as a topical calcineurin inhibitor (pimecrolimus or tacrolimus) is valuable for the face and folds where prolonged corticosteroid use risks atrophy. The American Academy of Dermatology guidelines affirm this potency-matched, course-defined approach as safe and effective. [6]

Steroid phobia — the unfounded fear of topical corticosteroids — is the commonest cause of under-treatment and must be addressed directly. The evidence, including the AAD guidelines, supports the safety of topical corticosteroids when potency is matched to site and they are used in defined courses with fingertip-unit dosing. I would explain this to the parents, demonstrate the fingertip unit, reassure them that the risk of skin thinning is negligible with appropriate use, and give a clear written plan specifying which cream goes where and for how long. [6]

b) Explain the atopic march and discuss what this child's parents should be told about prognosis and prevention. (4 marks) [2]

The atopic march describes the typical temporal progression from atopic dermatitis and food allergy in infancy to allergic rhinitis and asthma through the preschool and school-age years, underpinned by shared barrier-and-Th2-immune pathways. A 2019 review characterises it as multiple trajectories, in which early-onset, severe atopic dermatitis with early sensitisation predicts the most aggressive progression. Because this child has severe early-onset disease and a strong atopic family history, his risk of progressing to food allergy, asthma and rhinitis is elevated — up to 50 per cent for asthma in the most severe early-onset phenotype. [2]

I would tell the parents that atopic dermatitis follows a fluctuating relapsing-remitting course and that roughly half of childhood cases improve or resolve by adolescence, but that their son's early, severe presentation warrants aggressive skin control to interrupt the itch-scratch cycle and potentially modify the march. I would address food allergy proactively: foods sensitise through broken skin, so good barrier care matters, and I would reassure them that dietary restriction is not an eczema treatment, while advising early introduction of allergenic solids from around six months in line with current prevention guidance. Regular review, a co-managed approach to emerging wheeze or rhinitis, and a clear action plan are the practical mainstays of long-term care. [2]