24: Allergic Contact Dermatitis Flashcards
What is the primary cause of Allergic Contact Dermatitis (ACD)?
Allergic Contact Dermatitis is caused by skin contact with an environmental allergen leading to a cell-mediated (type IV) hypersensitivity reaction.
What are the three phases of Allergic Contact Dermatitis?
The three phases of Allergic Contact Dermatitis are:
1. Acute phase: characterized by pruritus, erythema, edema, and vesicles.
2. Subacute phase: involves vesicular rupture leading to oozing and scaly papules.
3. Chronic phase: presents as lichenified erythematous plaques with variable hyperkeratosis and pigmentary changes.
What is the significance of patch testing in the diagnosis of ACD?
Patch testing is the diagnostic test of choice to identify causal allergens and is indicated for patients with persistent or recurrent dermatitis in whom ACD is suspected.
How does age influence the prevalence of contact allergies?
Age influences the prevalence of contact allergies as follows:
- Adults 28-75 years: higher prevalence of allergy to fragrance.
- Adults 41-60 years: higher prevalence of allergy to preservatives.
What are the clinical features of Allergic Contact Dermatitis?
The clinical features of Allergic Contact Dermatitis include:
- Pruritic, eczematous dermatitis initially localized to the primary site of allergen exposure.
- Geometric, linear, or focal patterns of involvement suggestive of an exogenous etiology.
- Poison Ivy ACD presents as a linear or streaky array of erythematous papules and vesicles.
What is the role of Langerhans cells in the sensitization phase of ACD?
In the sensitization phase of ACD, Langerhans cells (a type of antigen presenting cell) take up the hapten-protein complex and express it on their surface, presenting it to naïve T cells in the lymph nodes, which is crucial for developing an immune response.
What is the median prevalence of contact allergy in the general population?
The median prevalence of contact allergy in the general population is 21.2%, with variations based on gender and specific allergens.
What are the two distinct phases in the development of Allergic Contact Dermatitis?
The two distinct phases in the development of Allergic Contact Dermatitis are:
1. Sensitization phase: lasts 10-15 days and is asymptomatic.
2. Elicitation phase: occurs upon subsequent exposure to the antigen, leading to an allergic reaction.
A patient presents with pruritic, eczematous dermatitis localized to the wrist. They frequently wear a nickel bracelet. What is the likely diagnosis and the diagnostic test of choice?
The likely diagnosis is Allergic Contact Dermatitis (ACD) caused by nickel. The diagnostic test of choice is patch testing.
What are the key phases of allergic contact dermatitis (ACD) and their characteristics?
- Sensitization Phase:
- Lasts 10-15 days, asymptomatic
- Initial exposure to allergen leads to immunologic memory formation.
- Elicitation Phase:
- Subsequent exposure to the same allergen triggers an inflammatory response, resulting in symptoms such as pruritus, erythema, and vesicles.
How does the prevalence of contact allergy differ by age and gender?
- Age:
- Adults 28-75 years: Higher prevalence of fragrance allergy.
- Adults 41-60 years: Higher prevalence of preservatives allergy.
- Gender:
- Median prevalence of contact allergy: 21.8% in women vs. 12% in men.
- Pierced ears are a significant risk factor for nickel allergy in women.
What clinical features are indicative of allergic contact dermatitis (ACD)?
- Classic Presentation:
- Pruritic, eczematous dermatitis localized to the site of allergen exposure.
- Patterns of Involvement:
- Geometric, linear, or focal patterns suggestive of exogenous etiology.
- Specific Types:
- Poison Ivy ACD: Linear or streaky erythematous papules and vesicles.
- Lichenoid ACD: Rare variant mimicking lichen planus.
- Pigmented ACD: Mainly described in Asian populations.
What is the role of hapten in the sensitization phase of allergic contact dermatitis?
- Hapten:
- Unprocessed allergens that are small, lipophilic molecules with low molecular weight (<500 daltons).
- They penetrate the skin and bind with epidermal carrier proteins to form a hapten-protein complex, which is essential for the immune response.
- Process:
- The hapten-protein complex is presented to T cells, leading to sensitization and subsequent allergic reactions upon re-exposure.
What are the steps involved in the sensitization phase of allergic contact dermatitis?
- Innate Immunity Activation: Release of cytokines (IL-1, IL-8, TNF-α, GMCSF).
- Antigen Presentation: Langerhans cells or dermal dendritic cells take up the hapten-protein complex and present it on HLA molecules.
- Migration to Lymph Nodes: APCs migrate to regional lymph nodes to present the HLA complex to naïve T cells.
- T Cell Priming: Naïve T cells differentiate into memory T cells, acquiring skin-specific homing antigens.
- Immigration into Circulation: Memory T cells circulate and act on target cells presenting the same antigen in the future.
What are the steps involved in the elicitation phase of allergic contact dermatitis (ACD)?
- Hapten exposure leads to low-grade nonspecific inflammation through cellular stress.
- Activation of toll-like receptors and nucleotide-binding oligomerization domain-like receptors results in neutrophil recruitment and effector T-cell recruitment.
- Interaction with APCs occurs in a cluster around postcapillary venules.
- Antigen-specific T cells release cytokines (INT-g and TNFa).
- An inflammatory response occurs, leading to monocytes migrating into the affected area, maturing into macrophages, and attracting T cells.
What are the misconceptions about allergic contact dermatitis (ACD)?
- ACD is not always bilateral, even when the antigen exposure is bilateral (e.g., shoe or glove allergy).
- Exposure to an allergen can be uniform (e.g., contact allergy to a cream), but eczematous manifestations are often patchy.
- ACD can affect the palms and soles.
What is the significance of the topographic approach in diagnosing allergic contact dermatitis (ACD)?
The topographic approach is crucial in diagnosing ACD as it is based on the distribution of dermatitis on the patient’s skin. This approach helps identify specific allergens related to the dermatitis patterns observed.
What are common allergens associated with eyelid dermatitis in allergic contact dermatitis?
Common allergens associated with eyelid dermatitis include:
- Tosylamide formaldehyde resin found in nail lacquer.
- Phenylmercuric acetate and antibiotics, which are preservatives frequently found in ophthalmic preparations.
What are the typical presentations of allergic contact dermatitis on the face and scalp?
Face: The prototypical presentation is preauricular facial dermatitis, often seen in nickel-allergic patients.
Scalp: PPD is a potent sensitizer used in hair dyes, causing intense scalp pruritus with scaling, edema, and crusting.
A 35-year-old hairdresser develops dermatitis on their hands. What allergen is most likely responsible, and what is the recommended diagnostic approach?
The most likely allergen is para-phenylenediamine (PPD) from hair dyes. The recommended diagnostic approach is patch testing.
A patient presents with erythema and scaling on the eyelids. They frequently use nail polish. What is the likely cause, and why are the eyelids particularly sensitive?
The likely cause is ectopic contact dermatitis from tosylamide formaldehyde resin in nail polish. Eyelids are particularly sensitive due to their thin skin and the accumulation of offending chemicals in eyelid folds.
A patient develops dermatitis on the lips after using a new sunscreen. What ingredient is likely responsible, and what is the condition called?
The likely ingredient is benzophenone-3 (oxybenzone). The condition is called allergic contact cheilitis.
A patient presents with dermatitis on the eyelids after using a new ophthalmic preparation. What allergens should be suspected, and why are the eyelids particularly vulnerable?
Suspected allergens include phenylmercuric acetate and antibiotics. Eyelids are particularly vulnerable due to their thin skin and the accumulation of offending chemicals in eyelid folds.
A patient develops dermatitis on the scalp after using a permanent wave solution. What chemical is likely responsible, and what are the clinical features?
The likely chemical is GMT (glyceryl monothioglycolate). Clinical features include intense scalp pruritus with scaling, edema, and crusting.