Psoriasis and Atopic Dermatitis — Different Conditions or one Spectrum?

Atopic dermatitis and psoriasis have long been considered two separate conditions, with different mechanisms of action, symptoms, and treatments. Recently, this idea has been challenged by two dermatology researchers who have published an article in the journal, Current Opinion in Immunology. These two individuals analyze the potential immune response pathways involved in both psoriasis and atopic dermatitis, each condition’s response to common treatments, and the demographic information of affected individuals. From their analysis, they hypothesized that these two conditions may not be so independent after all, and could exist on a spectrum, with various subtypes in between.

The role of T-cells

The researchers point out that both conditions are related to inappropriate immune system responses related to T-cells, specifically helper T-cells (also called Th cells). These helper T-cells mistakenly attack the body’s own tissues, as if they were dangerous, and then go on to produce more immune-related substances called cytokines. The underlying mechanism of psoriasis and atopic dermatitis may not be completely understood; however, many experts hypothesize that the inappropriate increase in cytokines within the body is what contributes to the inflammatory response responsible for these conditions. This is why both atopic dermatitis and psoriasis are often treated with broad scale immunosuppressive drugs or with specific cytokine antagonists (drugs that block the production of inflammation-causing cytokines).¹

Examining the inflammatory pathways

Upon researching this further, the researchers report that a major pathway involved in psoriasis is the immune response involving the Th17 cell and the cytokine IL-17 (interleukin-17). Medications that target IL-17 have strong success rates in controlling psoriasis. Atopic dermatitis on the other hand, mainly involves Th2 cells and IL-4 and IL-13, and moderately responds to treatments that target these components. However, the response to medication is often more successful for those with psoriasis on IL-17 antagonistic medications. This indicates that the understanding and treatment of psoriasis may be more advanced than atopic dermatitis. One other unique factor about atopic dermatitis and is that it is associated with an increase in IgE production, an antibody that triggers allergic responses. This also may provide an explanation as to why individuals with atopic dermatitis also commonly have allergies or asthma.

More research needed

Although it seems like each condition has its own set of pathways, symptoms, and treatments, the researchers felt like there was still more to be investigated. They looked at the immune system pathways affected in individuals with atopic dermatitis and psoriasis along with their demographic characteristics. This is when they found evidence pointing toward a spectrum between both conditions as opposed to a complete separation between them. Surprisingly, although many individuals demonstrated the classic molecular pathways of each condition, Asian individuals and children with atopic dermatitis demonstrated changes in both the atopic dermatitis-related and psoriasis-related pathways. Additionally, the physical symptoms and tissue characteristics of these individuals were also more of a hybrid of both conditions rather than one over the other.

This information, along with the fact that atopic dermatitis is not as controlled with the current cytokine-targeting medications on the market for it (when compared to psoriasis), led the researchers to determine that both psoriasis and atopic dermatitis may not be as separate as it was once thought. The researchers concluded that atopic dermatitis may be a multi-axial condition, meaning that its symptoms stem from multiple pathways, and it may share some of these with psoriasis. The authors call for further investigation on certain subgroups of individuals who may represent the overlapping or continuous part of the potential psoriasis—atopic dermatitis spectrum.¹