Central Sensitization and Ketamine Infusions

Author: Jay Joshi

Unfortunately, central sensitization is one of those conditions that's really not very well understood by most practitioners. It's not something that's taught in medical schools, it's not even been something that's been focused on in residency or fellowship programs. So, what's central sensitization? Well, to put it very simply, central sensitization is what happens when your brain is exposed to certain experiences or certain memories. It's life. It's being a human. This is something that happens to the neurophysiology of your brain. It forms memory. That's the same thing that happens with pain. When you have a chronic pain stimulus, usually one of the first things that happens is your brain says, "Hey, don't do that again." But what happens when that signal doesn't stop, and the brain keeps amplifying the pain? That's really the pathogenesis of what central sensitization is. When that process keeps occurring and that problem keeps worsening, that's when we see central sensitization disorders. Anxiety, depression, fibromyalgia, CRPS, or complex regional pain syndrome, RSD, PTSD, post-traumatic stress disorder, sometimes phantom limb syndrome, something else called opiate induced hyperalgesia. These are all forms of central sensitization.

Ketamine infusions have been around for many years. But for some reason, it's not very well understood by primary care physicians, or by pain management doctors. When you look at ketamine as a molecule, it's binding to a major receptor called the NMDA receptor, the N-methyl-D-aspartate receptor. That receptor is incredibly complex. It has many sub receptors, and there are many products that can bind to the NMDA receptor. So, ketamine can bind to this NMDA receptor and act as an antagonist, preventing it from firing. When it fires, in many situations, it's firing things like glutamate or glycine, which are excitatory compounds. When it keeps firing those excitatory compounds, that's when you start seeing this wind-up phenomenon occurring, where the body doesn't stop. So we want to try to bind that, and reset that receptor. And that's really what a ketamine infusion does, is it resets that receptor. Ketamine is even more complex than that, but the main mechanism is that NMDA antagonism. Ketamine infusion needs to be done by someone who has an intimate knowledge about the anesthetic drugs that are being used, about the side effects that could happen, about the interaction about those medications, about dosing of those medications, and really about tailoring that infusion so it works for that particular patient.

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