Central Sensitization and Chronic Pelvic Pain

Before we delve deeper into the role of Central Sensitization in chronic pain, let’s first understand what Central Sensitization really is.

What is Central Sensitization?

Central sensitization signifies slowly developing, plastic changes in the brain because of:

• the long-standing inflammation/disease state in the body AND/OR

• a feeling of a lack of safety in the psycho-social context (our environment)

Thus, making the brain act like an overprotective helicopter parent, who wants to know everything happening in the body, as well as outside of it (the environment). This makes us hyper-vigilant, making things even edgier as we go through a difficult pain flare.

How the body communicates with the brain when things are calm and safe

Each level of the spinal cord is responsible for getting information from a specific region to the body. For example, the S2 level of the spinal cord is going to receive information from the specific nerves from the pelvic region, the information that must be, then, relayed to the brain.

There are several different types of nerve fibers, each performing a unique function:⁣

• The 𝗔-𝗯𝗲𝘁𝗮 nerves bring info of light touch, for example, wearing an underwear or just stroking the skin over the genitals.
• The 𝗖 𝗻𝗲𝗿𝘃𝗲𝘀 bring information about unpleasant sensations called nociception i.e. unpleasant pressure, touch, temperature and chemical changes (inflammation). Contrary to popular belief, the body doesn’t have any pain receptors, only nociceptors. It may not sound like a huge deal, but when we label every unpleasant sensation as pain, it becomes easier for the brain to see those sensations AS pain. The degree of nociception is what is termed a threat/danger signal raised by the body.
• S2 level also gets information from the other levels above and below it, i.e. S1, L5, S3, etc. ⁣

All this information enters the dorsal horn of the spinal cord, where it gets blocked by the interneurons present there, acting as a spam filter so that the brain doesn’t get bothered unnecessarily and only receives relevant and important information. This allows the brain to keep everything in an orderly fashion and take action in a very specific, measured way.

To further ensure that this order is maintained, the brain also releases dampening chemicals such as dopamine, serotonin, and endorphins to suppress this information overload. These hormones are the body’s endogenous happy chemicals.

⁣⁣What happens in central sensitization 

However, what happens in central sensitization is that the C nerves release inflammatory chemicals that kill the interneurons in the spinal cord. And without the interneurons to block the excessive information, the brain starts to get bombarded with every tiny detail, which the brain perceives as dangerous. As the brain goes into overdrive, it also stops making the dampening chemicals, as it seeks more info to thwart the next imminent danger. It’s wartime!!⁣

This results in:

1. A never-ending vicious cycle of unnecessary info from A-beta fibers entering the brain. The more the brain is flooded with information, the more it perceives it as a threat, making us ever more hyper-vigilant and resulting in worsening pain. An example could be: ⁣the underwear touching the vulva or the scrotum is perceived as extremely uncomfortable/painful with a burning sensation. This is called Allodynia, meaning pain due to a stimulus that normally does not provoke pain.

2. The unpleasant information is relentless and the brain constantly feels that the injury to the tissue is ‘persisting’ and the body is under threat. As long as the brain keeps sensing the threat, it would keep dialing up the pain dial.

3. The other levels above and below the S2 level in the spinal cord i.e. L4, L5, S1 and S3, S4 will bombard S2 with info from other body parts, such as the lower back, buttocks, inner thighs (which would be blocked earlier by the interneurons), giving a feeling of pain spreading to the other areas of the body.

This is Central Sensitization in a nutshell! Reading about it, you might think that this nociplastic change in the brain is impossible to reverse. However, the research has found various strategies to be effective in controlling Central Sensitization. If you find this intriguing, then do read the ‘top and bottom up approaches’ blog post to understand this in even greater detail.

Hope you find this helpful!

Xx

Mukta