Contact dermatitis

Question 1

Definition

Answer 1

Skin reaction caused by an external agent.
Contact dermatitis can be either:
- Irritant contact dermatitis (ICD)
- Allergic contact dermatitis (ACD)

Question 2

Aetiology

Answer 2

ICD = direct toxicity by an agent
ACD = delayed hypersensitivity reaction

Question 3

Common allergens

Answer 3

Nickel sulfate
Neomycin
Formaldehyde
Sodium gold tiosulfate

Question 4

Epidemiology

Answer 4

• Occupation with frequent exposure to water and caustic material: compromise of the epidermal barrier allows penetration of allergens e.g. labourers, farmers, chefs
• Hx of atopy

Question 5

Signs

Answer 5

Acute onset:
- ICD = minutes to hours for severe irritants
- ACD = 24-72 hours if previously sensitised
Affecting hands and face
Sparing of non-exposed areas
Persistence of symptoms:
- ICD can take 3-6 weeks to resolve
- ACD usually resolves in a few days
Scaling: chronic contact dermatitis
Lichenfication: chronic contact dermatitis

Question 6

Symptoms

Answer 6

• Erythema
  -Pruritus: MC ACD > ICD
• Burning: MC ICD > ACD
• Vesicles: MC in ACD > ICD

Question 7

Pathophysiology

Answer 7

ACD requires prior sensitisation . Following re-exposure to the allergen, memory and effector T cells elicit an allergic response, typically within 48-72 hours causing erythema and pruritus .

ICD does not require prior sensitisation. The concentration of the irritant and duration of the exposure determine the severity of the response.

Question 8

Diagnosis

Answer 8

FIRST LINE:
- Skin patch testing: to identify allergen
- Repeated open application test: to reproduce ACD at application site

CONSIDER:
- Skin biopsy: variable findings in ICD including ulceration, parakeratosis and epidermal necrosis, ACD shows spongiosis and vesiculation with or without dermal and intra-dermal eosinophils

Question 9

Tx ICD

Answer 9

FIRST LINE = Avoidance of irritant
- Skin emollients: simple moisturisers
Second line:
Topical corticosteroids: hydrocortisone, betamethasone

Question 10

Tx ACD

Answer 10

FIRST LINE = Avoidance of allergen
- Topical corticosteroids : hydrocortisone, betamethasone

Second line: Topical calcineurin inhibitors:
- tacrolimus,
- pimecrolimus

Third line (or severe disease) options = Oral corticosteroids:
- prednisolone,
- dexamethasone
Phototherapy: BUVB, PUVA
Immunosuppressants:
- azathioprine,
- ciclosporin

Question 11

Complications

Answer 11

Secondary impetigo : bacterial infection due to compromised skin barrier
Post-inflammatory hyperpigmentation