Endometriosis Is a Nervous System Disease

My first excision surgery found endometriosis and removed it. I convinced myself the surgery would fix things. I remember that hope. This is it. I'm going back to my life.

The pain never went away. It shifted, became something harder to pin down. A pain that didn't match my imaging. A pain that seemed to live everywhere and nowhere. I started to wonder if I was losing my mind.

I wasn't. My nervous system had changed.

This is the piece of endometriosis that almost nobody talks about, and it's the piece that completely reshaped how I practice. Endometriosis isn't just a disease of the pelvis. After years of signaling danger to your brain, it can lead to changes in how your nervous system processes pain. Your brain learns that your pelvis is a threat. And once the brain learns something, the pain can persist even when the original tissue problem is addressed.

What Is Central Sensitization and How Common Is It in Endometriosis?

In a 2023 study of 285 women with endometriosis, 41% showed evidence of central sensitization — where the nervous system becomes hyperexcitable, lowering the pain threshold so that previously non-painful stimuli register as pain. This persists even after surgical lesion removal, explaining post-operative pain.

In a 2023 study of 285 women with endometriosis, 41% showed evidence of central sensitization using a validated questionnaire (the Central Sensitization Inventory). That's nearly half.

Central sensitization is when your nervous system becomes hyperexcitable — stuck in a state of amplified pain perception. The smoke detector in your house doesn't just go off when there's a fire anymore. It goes off at the smell of toast.

Chronic pain sends repeated signals to your spinal cord and brain. The system becomes hyperexcitable. The threshold for pain gets lower. A stimulus that used to register as "pressure" now registers as "pain." You feel pain in response to things that shouldn't hurt (allodynia) and feel a heightened response to things that do hurt (hyperalgesia).

This isn't your imagination. It's not psychological. It's a measurable change in how your nervous system processes sensory information. Brain imaging studies have shown that women with endometriosis-associated chronic pelvic pain have changes in brain chemistry and function, including alterations in gray matter volume and functional connectivity.

And even after you remove the source of the pain signals, even after surgery removes the lesions, the nervous system doesn't automatically reset. The alarm is still set to "hair-trigger." This is why pain can persist after technically successful surgery, and why reoperation rates after conservative surgery are reported as high as 50% within 5 years in some studies — pain mechanisms extend beyond the lesions themselves.

How Do Endometriosis Lesions Interact With Nerves?

Endometriosis lesions produce nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), attracting nerve fibers to grow toward and into abnormal tissue. Inflammatory molecules like IL-1β directly stimulate nerve growth, and macrophage-derived IGF-1 promotes nerve sensitization — with IGF-1 concentrations correlating with pain scores.

The story goes deeper than brain learning. The lesions themselves are interacting with nerves in complex ways.

Endometriosis lesions are characterized by coordinated nerve and blood vessel ingrowth. The lesions produce growth factors like nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). These chemicals attract nerve fibers to grow toward and into the abnormal tissue.

Research has shown that IL-1β (an inflammatory molecule) directly stimulates NGF expression in endometriosis, promoting local nerve growth around lesions. This nerve growth is associated with more severe deep dyspareunia (pain with deep penetration during sex).

Macrophages (immune cells) also play a role. They colocalize with nerve fibers in endometriosis lesions and produce insulin-like growth factor 1 (IGF-1), which promotes nerve sprouting and sensitization. One study found that IGF-1 concentrations in peritoneal fluid from women with endometriosis positively correlated with their pain scores.

The result is that endometriosis lesions can become densely innervated — wired to send pain signals directly to your spinal cord and brain.

Does Lesion Size Predict Pain?

The intensity of pelvic pain does not correlate with the number, location, or subtype of lesions — with one exception: deep disease in the posterior cul-de-sac correlates with dyspareunia. Women with minimal disease may have severe pain, while women with extensive disease may be asymptomatic.

The intensity of pelvic pain in patients with endometriosis does not correlate with the number, location, or subtype of lesions (with one exception — deep disease in the posterior cul-de-sac does correlate with dyspareunia).

Women with minimal disease (stage I) may have severe pain, while women with extensive disease (stage IV) may be asymptomatic. This disconnect between visible disease and pain experience is one of the most frustrating aspects of endometriosis for both patients and clinicians.

There are some nuances. For deep infiltrating endometriosis specifically, the depth of penetration does correlate with pain intensity — the most severe pain is seen when disease extends 6mm or more below the peritoneal surface. And the location of deep lesions correlates with specific symptoms: uterosacral ligament involvement correlates with dyspareunia, rectal involvement correlates with dyschezia (painful bowel movements), and bladder involvement correlates with dysuria.

But overall, the lack of correlation between lesion burden and pain severity supports the idea that pain mechanisms in endometriosis extend beyond the lesions themselves — involving peripheral sensitization, central sensitization, and systemic inflammation.

What About the Vagus Nerve and Inflammation?

The vagus nerve mediates a built-in anti-inflammatory pathway, releasing acetylcholine to suppress pro-inflammatory cytokine release including TNF-α. Vagus nerve stimulation has been shown to reduce inflammation in other conditions, though large clinical trials specifically in endometriosis are still needed.

Your body has a built-in system that connects your brain to your immune system. It's called the cholinergic anti-inflammatory pathway, and it's mediated by the vagus nerve — the longest cranial nerve in your body.

The vagus nerve connects your brain directly to your organs. When vagal efferent fibers are activated, they release acetylcholine, which signals immune cells to suppress pro-inflammatory cytokine release — including TNF-α.

This is a real, measurable pathway. Vagus nerve stimulation has been shown to reduce inflammation in conditions like rheumatoid arthritis and inflammatory bowel disease.

In chronic pain conditions like fibromyalgia, low vagal tone (as measured by heart rate variability) has been observed. The vagus nerve's anti-inflammatory properties may have therapeutic potential for inflammatory conditions broadly.

I want to be clear about what we know and don't know: while vagus nerve stimulation is being studied for various inflammatory conditions, there are no large clinical trials specifically in endometriosis. The concept that vagal tone can be influenced through breathing exercises and other practices is supported by some research, but the direct application to endometriosis pain is still theoretical.

Can Psychological Treatments Help With Pain?

In a landmark trial, Pain Reprocessing Therapy produced 66% pain-free or nearly pain-free results in chronic back pain — maintained at 5-year follow-up. While this was not in endometriosis, the mechanism may apply to the central sensitization component. A phase II trial also found that transcranial direct current stimulation significantly reduced pain in endometriosis patients.

In a landmark randomized controlled trial published in JAMA Psychiatry, people with chronic back pain underwent Pain Reprocessing Therapy (PRT). The treatment involved understanding the neuroscience of pain, reconceptualizing the pain as a learned response rather than a threat signal, and gradually reengaging with activities while monitoring for safety.

The results: 66% of participants randomized to PRT were pain-free or nearly pain-free at post-treatment, compared with 20% in the placebo group. A 5-year follow-up found that 55% of PRT participants remained nearly or completely pain-free.

I want to be clear: this study was in chronic back pain, not endometriosis. The researchers specifically selected patients with "primary" (nociplastic) pain — pain without identifiable peripheral pathology. Endometriosis is different because there IS identifiable pathology (the lesions themselves).

However, the mechanism matters. For the component of endometriosis pain that involves central sensitization and learned pain responses, the brain can potentially unlearn some of that amplification. Not by denying the pain or thinking positively about it, but by actually understanding how the nervous system works and helping it recalibrate.

There is emerging research specifically in endometriosis. A phase II randomized controlled trial found that transcranial direct current stimulation (tDCS) significantly reduced pain in women with endometriosis and chronic pelvic pain compared to placebo. Biopsychosocial approaches including cognitive behavioral therapy (CBT) and acceptance and commitment therapy (ACT) have also been found effective in reducing pain and improving outcomes for chronic pelvic pain.

What Is Neuroplasticity and Why Does It Matter?

Research in mouse models of endometriosis has demonstrated neuroplasticity at both peripheral and central sites — including activation of immune cells in the spinal cord and enhanced pain signaling. If chronic pain can wire the brain to expect danger, gradual safe re-engagement may create new neural pathways.

The word that matters here is neuroplasticity. Your nervous system isn't a fixed circuit. It's constantly rewiring itself based on what you do, what you practice, what you pay attention to.

Research in mouse models of endometriosis has demonstrated that the disease causes neuroplasticity at both peripheral and central sites — changes in how sensory neurons respond and changes in spinal cord circuitry. The mice developed microgliosis (activation of immune cells in the spinal cord), astrogliosis, and enhanced pain signaling.

If chronic pain can wire the brain to expect danger, then gradual, safe re-engagement with movement and sensation can potentially create new neural pathways. This doesn't mean "mind over matter." It means understanding that your pain is real, your nervous system's learning is real, and the capacity to reshape that learning may also be real.

What Does Comprehensive Treatment Look Like?

Pain in endometriosis is multifactorial — involving nociceptive pain (from inflammation), neuropathic pain (from nerve involvement), and nociplastic pain (from central nervous system changes). Effective treatment needs to address multiple mechanisms simultaneously, not just lesion removal.

If you've had surgery and your pain persists, asking "Did they get it all?" might be the wrong question. A better question is: "What are all the factors contributing to my pain?"

Pain in endometriosis is multifactorial, involving nociceptive pain (from inflammation around lesions), neuropathic pain (from nerve involvement), and nociplastic pain (from central nervous system changes). Effective treatment may need to address multiple mechanisms.

That might mean treating the endometriosis itself through hormonal suppression, excision surgery, or other interventions to reduce the inflammatory and hormonal drivers. It might mean working with someone trained in pain science, neuroscience-informed therapy, or neuromodulation to address central sensitization. Many women with endometriosis develop pelvic floor dysfunction as a consequence of chronic pain, and managing comorbid conditions like irritable bowel syndrome or interstitial cystitis may also be part of the picture.

And this is what gets me emotional when I think about it: your brain is plastic. Capable of change. This doesn't mean your pain is your fault. But it does mean it's not necessarily permanent. You're not stuck with the alarm setting your nervous system learned.

You can teach it something different.