Intrinsic Versus Extrinsic Atopic Dermatitis

Over the past few decades, researchers and clinicians have discovered that there are two forms of AD: intrinsic (nonallergic) and extrinsic (allergic). Although the two forms are clinically indistinguishable based on the findings of the physical examination, there are numerous differences in other aspects (see Table 1 ). Extrinsic AD composes 70% to 85% of atopic dermatitis, while intrinsic atopic dermatitis makes up the remaining 15% to 30%. Extrinsic AD is associated with high serum IgE levels, exhibits allergen-specific IgE to aeroallergens and foods, positive skin prick reactions, and has a cytokine profile of high IL-4 and IL-13 levels (Bardana, 2004). IL-4, IL-5, and IL-13 cytokines play a role in the Th2 response which is seen in the early stages of AD. Chronic atopic dermatitis lesions principally have a Th1 response with the cytokines IL-12 and interferon-playing a dominant role (Schmid-Grendelmeier, Simon, Simon, Akdis, & Wuthrich, 2001). Patients with intrinsic AD, by contrast, have normal IgE levels, negative skin prick reactions, low IL-4 and IL-13 levels, and they do not have allergen-specific IgE to aeroallergens and foods (Bardana, 2004). The onset of extrinsic AD typically is in early childhood while patients with intrinsic AD have a later onset. Finally, patients with intrinsic AD are characterized by an absence of other atopic disease, asthma, and allergic rhinitis (Schmid-Grendel meier et al., 2001).