Differentiating Atopic Dermatitis From Psoriasis and CTCL

When we're caring for atopic dermatitis patients, sometimes skin biopsies are an incredibly important tool to differentiate between atopic dermatitis, psoriasis, and even in rare cases, cutaneous T-cell lymphoma. So let's break that down. When we think about our difficult patients that have sort of that overlap between atopic dermatitis presentation and psoriasis presentation, it can be a real challenge to us as the clinician to understand, well, which disease is it and how do we advise our patients?

Because in general, we think about the atopic dermatitis treatments and the psoriasis treatments differently, and we don't want to treat the patient with the wrong class or group of medications. But what we know from a lot of science, including transcriptomic analyses, is that there is an overlap in some of the gene expression and cytokine signaling between atopic dermatitis and psoriasis, which can make it very difficult to distinguish.

In some cases, a skin biopsy can be very helpful for elucidating a more psoriasis-like histologic pattern or a more atopic dermatitis-like histologic pattern. There's also those difficult patients that are not responding to therapy. You think that they have atopic dermatitis, you're putting them on either a biologic or an oral JAK inhibitor, and they're just not getting better.

You always have to have in the back of your mind, you have to always understand that there is a risk for cutaneous T-cell lymphoma. And cutaneous T-cell lymphoma is very well-known to mimic atopic dermatitis. And in chronic atopic dermatitis patients, there's a thought that it can emerge in those patients, the CTCL. There's even more reports recently about dupilumab possibly being linked to increased risk of cutaneous T-cell lymphoma.

There's still a lot of questions about that research and science in terms of is it really atopic dermatitis from the start? Is it CTCL from the start that's being a masked? Is it really a causative effect from the drug? These are questions we don't have the answer to, but what we do know as a clinician is that if you have a patient that's not responding the way you think, getting a skin biopsy can be very helpful, because CTCL on histopathology is very distinguishable from atopic dermatitis or psoriasis.

And as a case example, a few years ago, I was examining a patient with chronic hand eczema and this patient had failed numerous therapies. And when the patient came to me, I was seeing him for the first time and I did a skin biopsy and identified cutaneous T-cell lymphoma. That's published as a case report. You're welcome to go read it. The key point is keeping an open mind that those difficult patients not responding the way you think may need a little bit more care.