Eczema

Question 1

What is atopic dermatitis?

Answer 1

Type 1 hypersensitivity reaction that most commonly affects infants and children, causing itchy, dry skin in affected areas.

Question 2

Describe the pathophysiology of atopic dermatitis.

Answer 2

1. Allergen invades skin, recognised by antigen presenting cell.
2. Presented to naive T helper cell which gets activated to a Th2CD4 cell.
3. Th2CD4 cell stimulates B cell to make IgE antibodies specific to the allergen.
4. Antibodies bind to surface of mast cells and basophils (sensitisation).
5. Second ‘invasion’ causes cross-linking of the IgEs, causing degranulation.
6. Histamines, leukotrienes and proteases are released, causing inflammation.
7. Blood vessels become dilated and permeable, bringing more immune cells to the skin.
8. Skin becomes more permeable, allowing allergens in and water out. -> dry, scaly, itchy skin -> vicious cycle.

Question 3

Why does atopic dermatitis mostly affect infants?

Answer 3

They have thinner skin so allergens can easily invade.

Question 4

Describe the distribution of atopic dermatitis lesions.

Answer 4

Children: flexor surfaces - back of knees, insides of elbows, creases of wrists; Exposed areas: face, hands, feet
Infants: face, scalp.

Question 5

Describe the skin in atopic dermatitis.

Answer 5

Erythematous, dry, scaly skin.

Thickening due to repeated rubbing

Question 6

What does chronic eczema cause?

Answer 6

Thickened, lichenified (leathery) skin.

Question 7

What investigations would you do for eczema?

Answer 7

(Clinical)
Serum IgE - raised at T1 hypersensitivity.
Check vitamin D levels

Question 8

What would you see on histology for eczema?

Answer 8

Collection of fluid in the epidermis between keratinocytes and upper dermal perivascular lymphohistiocytic cells.

Question 9

Give 3 things which may exacerbate eczema

Answer 9

Wool
Detergents
Perfumes and cosmetic products

Question 10

Describe the management of eczema.

Answer 10

Education and explanation
Avoidance of irritants/ allergens
Emollients - more compliance, more improvement
Topical:
corticosteroids
immunomodulators -> Calcineurin inhibitors - tacrolimus, ciclosporin.

Question 11

What may cause recurrent skin infections?

Answer 11

Herpes simplex virus.