Allergic contact dermatitis Flashcards
Dermatology
Define allergic contact dermatitis?
Delayed, type 4 hypersensitivity reaction to exogenous, specific allergen
Define irritant contact dermatitis?
Nonspecific, immediate reaction to direct contact with physical or chemical agent
What is the main difference between allergic and irritant contact dermatitis?
Allergic: Delayed response to specific allergen
Irritant: Immediate response to non-specific irritant
Are allergic and irritant contact dermatitis more common?
Irritant contact dermatitis is more common than allergic contact dermatitis
Describe the pathophysiology of irritant contact dermatitis?
Excessive exposure to irritant strips the epidermis of protective, waterproofing lipids
Removes moisture
Penetration of irritant
Describe the pathophysiology of allergic contact dermatitis?
Sensitisation: 48-72 hours after initial exposure to allergen
T-lymphocytes become sensitised to specific allergen antigen
After re-exposure, CD4+ lymphocytes activates macrophages to release cytokines, CD8+ lymphocytes cause direct toxicity
What are the 4 hallmark features of acute contact dermatitis?
Erythema
Blistering (edemas)
Crusting
Weeping due to pus
What are the 5 hallmark features of chronic contact dermatitis?
Erythema
Lichenification
Hyperpigmentation
Scaling
Fissures (tiny cracks/cuts due to areas of dried, cracked skin that thicken over time)
What are contact dermatitis fissures?
Tiny cracks/cuts due to areas of dried, cracked skin that thicken over time
Describe a sensation that distinguishes allergic and irritant contact dermatitis?
Allergic: More pruritic
Irritant: More burning and stinging
How is contact dermatitis diagnosed?
Clinical diagnosis based on speed of onset and correlation of symptoms with exposure
Why would you perform a skin swab to investigate contact dermatitis?
Skin swab to confirm if a viral or bacterial infection has caused it, can also guide treatment
Why would you perform a patch test to investigate contact dermatitis?
Patch test to confirm if a particular substance/allergen is causing it, but not necessary if obvious allergen is identified
Is a patch test necessary to diagnose contact dermatitis?
No, but can be helpful if the allergen/irritant isn’t obvious
How does is a patch test performed on a patient throughout the week, to investigate contact dermatitis?
Patient attends on monday to have small samples of allergens and irritants placed on back, come back on wednesday and friday for skin inspection to identify degree of reactions to different substances
