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Psoriasis and seborrheic dermatitis are often viewed as overlapping conditions, but a recent investigation found no clear connection between the diseases.

The systematic review and network meta-analysis, published in , found that the overall rate of psoriasis in patients with seborrheic dermatitis was 2.1%, with no clinical association emerging.

Co-author Raj Chovatiya, MD, PhD, is a dermatologist and associate professor at Rosalind Franklin University of Medicine and Science in Chicago. The exchange with the Reading Room has been edited for length and clarity.

What prompted you to undertake this study?

Chovatiya: People often think about seborrheic dermatitis as a disease that often exists in a spectrum of other conditions. Psoriasis is one common example of these. For instance, people use terminology like "sebopsoriasis" to indicate an overlap state between the two.

The question for our study was based on the fact that we understand so little about seborrheic dermatitis purely as a disease state. Psoriasis was a great first disease to look at just given the fact that people often think of these diseases as coexisting.

Your key conclusion contrasts with common presumptions. Can you say more about this?

Chovatiya: While people commonly think about the diseases as co-occurring and existing on a similar spectrum, emerging immunologic evidence suggests these are actually distinct disease states, and our data would seem to line up with that.

Evidence does suggest that there is comorbid psoriasis, but we found that there are not too many such cases, and there wasn't a very clear or statistically significant association between the two entities.

What do you hope dermatologists will take away from your study?

Chovatiya: We've seen therapeutic advancements across multiple inflammatory diseases, including seborrheic dermatitis. Our ability to differentiate among these diseases and pursue the right treatment for the right disease is important, especially when we're trying for optimal responses.

Secondly, I think being very deliberate in the way that we explain this to colleagues and patients is important because I want to be accurate in explaining what I think is going on. Being able to put the right name on their disease entity is important.

So, the biggest take-home is accuracy -- with diagnosis, with wording, and with treatment.

How might the dermatology community evolve in this area over the longer term?

Chovatiya: We probably need to better understand the baseline for people who come in with seborrheic dermatitis. We need better understanding of disease factors and the natural course of the disease, and how comorbidities might develop.

I'm hoping we'll all take an interest in trying to better understand what we've historically thought of as a pretty straightforward disease. We're only now beginning to understand that seborrheic dermatitis is not only immunologically complex but can pose big burdens on our patients' quality of life.