ATOPIC DERMATITIS – MECHANISMS AND TRIGGERS (Madeleine W. Sumpaico, M.D.) 

The pathophysiology of atopic dermatitis (AD) is the result of an interplay between susceptible genes, host environments, infectious agents, defects in skin barrier function and immunologic responses. The inflammatory response of the AD skin is characterized by the activation of T lymphocytes, dendritic cells (DC), macrophages, keratinocytes, mast cells and eosinophils.

TH2- and TH1-type cytokines contribute to the pathogenesis of skin inflammation in AD, with the relative contribution of each cytokine dependent on the stage of skin inflammation.  

The acute skin lesion is associated with a predominance of TH2-like cytokines ( IL4 and IL13), whereas maintenance of chronic inflammation is associated with an increase of TH1 and TH2 cytokines ( IL5, GM-CSF, IL12 and IFN-g) accompanied by the infiltration and prolonged survival of eosinophils and macrophages. Chemokines further reinforce the influx of inflammatory cells into the skin. Mechanical trauma from scratching and microbial toxins induce the release of proinflammatory cytokines (TNF-a) that perpetuates and elicits skin inflammation.

 Atopic dermatitis can be triggered by a variety of allergic and non-allergic stimuli. The allergic triggers include food allergens, aeroallergens and microbial toxins. Skin prick tests and measurement of specific IgE can be used to assess for sensitization to food and inhalant allergens. The Atopy Patch Test (APT) can be used to assess the response in the skin.
 
Environmental factors can also cause exacerbation of the disease. These factors include climate changes, chemical and physical irritants and psychosocial stressors. 
 
Atopic dermatitis usually is diagnosed by its typical clinical presentation. The standardized major and minor criteria by Hanifin and Rajka for the diagnosis of AD has brought together the clinical syndrome of AD. Presently, there are no diagnostic laboratory test to confirm the diagnosis of atopic dermatitis.  Skin biopsies are not essential for the diagnosis but might be required to exclude other diagnosis, particularly in adults.