The 101 on Itch With Dr Brian Kim

With research beginning to focus more on atopic dermatitis (AD) and its most prominent symptom of itch, Brian Kim, MD, MTR, FAAD, lectured on how to measure itch and understanding the data in practice at Dermatology Week 2021. Dr Kim is an associate professor of dermatology and 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.

Itch is a central feature of AD, and Dr Kim explained that the paradigm of AD pathogenesis and the role of itch in this is evolving. Various allergen and inflammatory stimuli can cross the leaky skin barrier and can activate the adaptive antigen-specific T helper 2 cells, IL-4, and IL-13. Those cytokines induce the production of IgE, a hallmark feature of atopy, as well as directly cause more inflammation and damage to the barrier, thereby contributing to the itch-scratch cycle. More recent research has identified the upstream role of IL-33 and thymic stromal lymphopoietin as well as a downstream role of basophils and innate lymphoid cell 2.

“For everyone to be on the same page, it’s very important to understand how itch transmission occurs within the skin,” said Dr Kim. Classically, a neurotransmitter binds to a receptor to open a cation channel, causing depolarization when ions cross the channel. If enough passage occurs, then an action potential is triggered, opening a voltage-gated sodium ion channel, which then sends another action potential to the spinal cord. A similar process follows in the spinal cord, which eventually transmits the message to the brain, triggering the perception of itch.

Currently, itch is measured on a numerical rating scale (NRS), with a score of 0 representing no itch and 10 representing worst itch imaginable. The NRS has been useful in practice and in clinical trials, even for diseases such as prurigo nodularis and chronic pruritus of unknown origin, and can show the increasing links to other patient-reported outcomes.

However, the NRS does not capture the impact of acute flares. The pattern of acuity of itch in AD may influence the patient’s perception of their disease and alter the definition of severity. Dr Kim stressed that clinical trials may be evaluating efficacy based on a mean NRS instead of objectively evaluating the itch pattern distribution, and dermatologists should remember that acute itch flares are dynamic and much more prominent in the patient population than previously thought.

To build on this knowledge, Dr Kim connected acute itch flares with allergen-specific IgE. While the science is still novel, he highlighted a study by Wang et al published in Cell that provokes “the hypothesis that this [IgE] reactivity is biologically meaningful, and that reactivity to environmental allergens is likely, in part at least if not significantly, driving these acute itch flares.”

Dr Kim shared an exciting development for an objective measurement of itch, describing a touchless technology called Emerald. The radiofrequency technology can track factors such as sleeping, and scratching, both factors important in the quality of life of patients with AD. In a few prospective observational studies, Dr Kim’s research group demonstrated that scratching impacts the number of awakenings during sleep, negatively affecting sleep efficiency.

“So the conclusion of this is that we can perhaps measuring scratching objectively, and scratching can actually reveal hidden morbidities that patient-reported outcomes cannot capture,” added Dr Kim. The next step will be understanding how objective measurement of itch may be influenced by different disease states.

Reference
Kim BS. Measuring itch in atopic dermatitis. Presented at: Dermatology Week 2021; September 16-19, 2021; virtual.