In this video, Brian S. Kim, MD, MTR, FAAD, outlines the vicious cycle, from inflammatory cytokines to barrier disruption and pruritus, behind the most burdensome symptom of atopic dermatitis. Dr Kim is an associate professor of dermatology as well as the co-director of the Center for the Study of Itch and Sensory Disorders in the division of dermatology, department of medicine, at Washington University School of Medicine in St Louis, MO.
Dr Kim: When we talk about the itch‑scratch cycle, essentially what we're talking about is that you start with either itching or inflammation, and then what happens is that you start scratching. Then you cause damage to the barrier.
We know that in eczema, having inflammation in the skin is enough to cause damage to a barrier, and then that there are many individuals who have a defective barrier to start with. All of that can be aggravated by scratching, and then, of course, with this scratching what can very much happen is that you can have proteins, or called cytokines, released from either the top layer of the skin, the epidermis, that then activate other cells and immune cells that are deeper in the skin, the second deeper compartment, the dermis. Those in turn release even more proinflammatory factors that then propagate inflammation, as well as itch. That's what we mean by the cycle, that it's essentially a vicious cycle of itching, scratching, inflammation, and then you get to a point where, in severe cases of eczema, it's very difficult to control.
The work of my lab focus now on if the barriers compromised, what happens? What we find is that the skin cells in the top layer of the epidermis, or when that barrier starts to breakdown, they become very unhealthy. They become angry, and they start releasing these cytokines. Then they set off this cascade of inflammation and itch. These cytokines, IL‑13, which are classical cytokines associated with not just atopic dermatitis, but allergic inflammation. These cytokines are very important in that they are the molecules that translate what happens in the immune system to the nervous system and promote itch. There are other cytokines too that are very important, like IL‑31.
What's been very important for us is that to see that these therapeutically are validated as being important. We know this with the drugs that are either available or in development, that they do have very profound effects on itch. It's probably in part due to being able to disrupt what we call, the buzzword nowadays is, neuroimmune interaction between the immune system and the nervous system.
A lot of treating eczema is about the patient understanding their disease. In many ways, I felt my approach to treating eczema has been very homeopathic. In that, the most important component is taking a multidisciplinary approach. Empowering the patient to fully understand what phase of their disease they're in at each moment.
There are moments when that barrier itself is more important. Heavy moisturization becomes the primary modality that you need to lean on. There are other moments in having eczema where you have to understand that, "Oh, I'm not just having dry skin, I'm actually having a lot of inflammation. I need to be very aggressive with topical steroids." It is very time and context dependent.