From the Guidelines
The underlying cellular mechanism in this landscaper's contact dermatitis involves a type IV delayed hypersensitivity reaction, which occurs when allergens penetrate the skin, bind to carrier proteins, and induce an inflammatory cascade upon re-exposure. This reaction is characterized by the processing of antigens by Langerhans cells in the epidermis, which then migrate to regional lymph nodes and present the antigens to T lymphocytes 1. Upon re-exposure to the allergen, sensitized T cells release pro-inflammatory cytokines, recruiting additional inflammatory cells to the site, leading to the clinical manifestations of pruritus, burning pain, and rash on the exposed upper extremities. The most recent and highest quality study on the management of contact dermatitis, published in 2017, highlights the importance of identifying and avoiding the triggering allergen, as well as the use of topical corticosteroids to reduce inflammation and potentially antihistamines to manage pruritus 1.
Some key points to consider in the diagnosis and management of contact dermatitis include:
- The cause of contact dermatitis is frequently multifactorial, and patients may have irritant and/or atopic/endogenous dermatitis in addition to allergic contact dermatitis 1
- Patch testing is an essential investigation in patients with persistent eczematous eruptions when contact allergy is suspected or cannot be ruled out 1
- The sensitivity of patch testing ranges from 60-80% in reports, and positive patch tests only indicate contact sensitization and need demonstrated relevance to the patient's active dermatitis 1
- Avoidance of the suspected allergen with resolution of the corresponding dermatitis confirms the diagnosis of allergic contact dermatitis 1
In terms of the specific cellular mechanism involved, it is worth noting that:
- Allergens bind to epidermal carrier proteins to form complete antigens, causing sensitization and inducing an inflammatory reaction on subsequent exposure 1
- The reaction typically develops 24-72 hours after allergen exposure, distinguishing it from immediate hypersensitivity reactions 1
- The inflammatory cascade leads to the recruitment of additional inflammatory cells to the site, resulting in the clinical manifestations of pruritus, burning pain, and rash on the exposed upper extremities 1
From the Research
Underlying Cellular Mechanism
The underlying cellular mechanism involved in the patient's diagnosis of contact dermatitis is a delayed hypersensitivity reaction. This reaction is mediated by previously sensitized T helper cells that are activated by an antigen, initiating an inflammatory cascade 2.
Key Features of the Mechanism
- The patient's occupation as a landscaper increases the risk of exposure to potential allergens such as poison ivy, which can cause allergic contact dermatitis 3.
- The symptoms of intense pruritus, burning pain, and a rash on the bilateral upper extremities are consistent with allergic contact dermatitis 3, 4.
- The linear arrangement of vesicles and plaques with overlying excoriations on the forearms suggests a delayed hypersensitivity reaction to an allergen that came into contact with the skin 3.
Comparison of Options
- Option 1: Antibodies bind to an antigen, inducing the complement pathway and membrane attack complexes. This is not the primary mechanism involved in contact dermatitis.
- Option 2: Antigens crosslink with IgE, thereby inducing mast cell degranulation. This is more characteristic of an immediate hypersensitivity reaction, not a delayed hypersensitivity reaction like contact dermatitis.
- Option 3: IgM or IgG antibody-antigen immune complexes deposit into tissue, thus activating complement. This is also not the primary mechanism involved in contact dermatitis.
- Option 4: Previously sensitized T helper cells activated by an antigen initiate an inflammatory cascade. This is the correct mechanism involved in contact dermatitis, as it is a delayed hypersensitivity reaction mediated by T cells 2.