What is hyperalgesia? What is allodynia?

Two of the most commonly used terms in the pain research and medicine world are hyperalgesia and allodynia. The word hyperalgesia means an increased response to a painful stimulus. The word allodynia means a painful response to a normally innocuous stimulus.

Here is an example of hyperalgesia: if your arm was pricked by a pin and you said that it gave you 3 out of 10 pain this would be your baseline response. If an experimenter then gave you some injection (let’s say capsaicin — the pungent ingredient in hot peppers) and then 30 minutes later pricked you with the pin again and you reported 6 out of 10 pain this would be hyperalgesia. For hyperalgesia to occur it is important for the stimulus to be painful to begin with. Remember that hyperalgesia is always an increased pain response to a noxious stimulus.

Here is an example of allodynia: if an experimenter brushed your arm with a cotton bud (like a q-tip) you would almost certainly say that the stimulus was not painful — 0 out of 10. If the experimenter then injected your arm with capsaicin and brushed your arm again 30 minutes later you would likely report that it was painful — let’s say 4 out of 10 pain. This is an allodynia, a painful response to an innocuous stimulus. In order for allodynia to occur the stimulus MUST NOT normally be painful.

Some small changes around here… UPDATED

In the past my posting has been more or less random. We’ve had some themes from time to time and a series or two most of which were never really tied up. Over the past few days I became aware of a fellowship from a foundation that covers the topic of pain and society. The idea of the fellowship is to bring a select group of people in, on an annual basis, to learn about effective communication for pain treatment and pain research advocacy. Coupled with the education aspect of the fellowship are numerous opportunities to get involved by talking to Congress, funding agencies and state and local legislatures. I will be applying for one of these fellowships next year.

As part of the application, the potential fellow is supposed to provide evidence of an innovative approach to educating the public (or medical practitioners) on the unique problems that pain management presents for medical practice or on the importance of funding pain research. I’ve decided that blogging is an excellent way to demonstrate that I have a unique approach (as far as I know I’m the only pain researcher with an active blog — in English at least) and I am going to dedicate more of the blog time to building a portfolio of pain-related posts (under the new “pain” category). You can still expect some of the same old garbage and some insightful posts on being a junior tenure-track faculty along the way, I promise. In the mean time we’re going to start by de-mystifying some of the pain research (and medicine) terminology to enlighten a general audience on what this stuff actually means. Mixed in we’re going to go into some pharmacology and some basic neuroscience of the pain pathways (geared toward a lay audience). Through all of these posts I hope to point out why pain research is so important, how and why current analgesics are inadequate in many situations and what a pervasive problem chronic pain is in the US and the world.