The itch roundtable

When I heard back in December about the NIAMS (division of the NIH) itch roundtable--a discussion that involved the NEA's CEO Julie Block, a number of NIAMS directors, and a larger number of active itch researchers--I was excited that the meeting summary would be made public. I don't know why it is, but in the media you hear about eczema much more from the allergy perspective, or as if it's a cosmetic issue with dry skin, rather than the reality for a lot of us: chronic itch. If we could control the itch, we'd be less at risk of infection, we wouldn't prolong our flares, and possibly most importantly, we'd have more self-respect.

It's hard to feel like you're a grown-up when your self-control in this one dimension is no better than a three-year-old's.

The summary of the itch roundtable was recently put online (at the link above). I got there by following a link in the email the NEA sent all its members. At the end of the summary there's a long list of the participants. I plan to check out what research they're all doing.

Two things jumped out at me from the summary. The first thing is that itch research is building on the much more established field of pain research. It appears well-known that certain types of pain can inhibit itch. (And, in fact, that the same type of neuron carries both impulses.) As an eczema patient I know this very well first-hand. In fact, sometimes scratching feels good precisely because it hurts, and seems to spread a cool blanket of pain over the burning itch.

I've got a rather silly story to relate about this. When I was a teenager I discovered this pain-itch connection, and I happened to have an itchy scalp at the time. I found that a good way to relieve the itch was to pull out small clumps of hair. Ouch! you say. Ouch is right. Felt great. I did this for about a week.

The problem was that I then developed an extremely nasty case of something like eczema herpeticum--little fluid-filled blisters that spread all over my body and threatened to leave me looking sandblasted for life. Fortunately my parents took me to a doctor who prescribed some magical cream that completely reversed the infection. I have no idea what the cream was, only that it worked, and that my parents said it was "very strong." It must have been an antibiotic of some kind.

Dr. Sib, if she still reads this blog--will remember this episode. During the recovery period, I drove her crazy by picking at my scabs.

So don't try that at home.

The second thing that jumped out at me from the summary was that, although mice are the standard laboratory model animal for many human diseases, there are several key reasons why itch in mice and humans is substantially different at the molecular level and at the level of the skin as an organ. Therefore, it's unlikely that a mouse model will be developed for human itch. To quote NIAMS:

• Itch- and pain-specific neurons and receptors identified in mouse models may not have the same distinct functions in humans.
• Structural differences in mouse and human epidermis may create differences in itch transduction, and downstream cellular activity (e.g., protease production).
• Overexpression of many cytokines in mice will induce non-specific itch, whereas the itch mechanisms in humans appear to be more complex.
• Current mouse models correspond to acute itch, whereas clinical itch tends to be chronic.
• Linking itch mechanisms from animal models to the spectrum of itch descriptions in human patient populations can be challenging, because some behaviors in animal models, such as scratching, licking, and biting that are attributed to the condition may be unrelated to it.

These complications with animal models will slow itch research. But pain research has faced similar hurdles, and is more advanced as a field, so we can hope the scientists can piggyback their work on existing pain research.