What is endometriosis?
- Endometriosis is when tissue that is similar to (but not the same as) the tissue that lines the uterus grows OUTSIDE of the uterus. About 1 in 10 women of reproductive age have it.
- This can cause a variety of symptoms: chronic pelvic pain, heavy or painful periods (dysmenorrhea), abdominal pain, trouble getting pregnant, constipation, bladder problems or painful bladder syndrome, low back pain, TMJ dysfunction (temporomandibular joint dysfunction) and more.
Doctors often treat endometriosis with hormonal therapy or surgery (to remove the abnormal tissue). But here’s the thing: many people don’t get better with just that approach.
- Around 18–27% of people on hormonal treatment don’t get any relief.
- About 20% still have chronic pain even after surgery to remove lesions.
- Even more puzzling: many people with chronic pelvic pain don’t have lesions in the places where they feel pain, or still have pain after the painful lesions have been removed.. In fact, 70–80% of them have no visible lesions in those painful spots.
So … how can endometriosis cause pain — even when the endometriosis tissue is gone or not near the painful area? That’s where sensitization comes in.
Sensitization: What Happens When Your Nervous System Gets “Wired Wrong”
You might think of sensitization like a radio whose volume knob gets stuck on high — so even quiet, normal signals become unbearably loud. In the body, sensitization means your nervous system becomes overly sensitive, so everyday sensations (or mild pain) are felt as intense pain.
Two stages: Peripheral sensitization → Central sensitization
- Peripheral sensitization happens first. It’s like the first time you get hurt — say a cut, inflammation, or irritation from endometriosis lesions. Pain signals fire, the body sends immune cells to help, and nerves get “irritated.” Over time, if those pain signals keep coming, the pain receptors become more sensitive so they fire more easily.
- If that continues over a long period, the changes can reach deeper — into the central nervous system (brain + spinal cord). That’s where central sensitization happens.
Once central sensitization sets in:
- The nervous system becomes over-reactive.
- Things that shouldn’t be painful — like light touch, pressure, or even normal muscle movement — can hurt. (This is called allodynia.)
- Things that were only slightly painful before can feel much worse (hyperalgesia).
- Pain can linger — even if the original problem (like an endometriosis lesion) is gone.
In other words: once the nervous system gets rewired for “pain mode,” it stays that way. It’s not just about damaged tissue anymore — the nervous system itself starts treating routine signals as threats.
Why Endometriosis + Sensitization Go Hand-in-Hand
- In endometriosis, the constant irritation and inflammation from lesions may repeatedly activate pain nerves (nociceptors), pushing those nerves into a more sensitive state.
- Also, endometriosis can affect nerves and blood vessels. These abnormal nerve connections and inflammatory chemicals can make the nervous system more “trigger-happy.”
- Over time, this can lead to myofascial trigger points — tight, painful “knots” in muscles and connective tissue. These can themselves cause pain, even independent of endometriosis lesions.
- Because of how the nervous system is wired, pain can show up “somewhere else” than where the original problem was. For instance: bladder issues may lead to lower-back or abdominal muscle pain. This happens because signals from organs (like the bladder or uterus) and surrounding muscles get mixed up in the spinal cord. This is called viscerosomatic convergence.
That’s why, for many people, removing the endometriosis tissue through surgery doesn’t eliminate pain — because the nervous system itself has changed.
How Do You Know If You Have Central Sensitization?
- There’s a questionnaire called the Central Sensitization Inventory (CSI). It helps doctors see if someone’s pain is likely driven by sensitization rather than ongoing tissue damage.
- In people with endometriosis, a score of 40 or higher often indicates central sensitization, and is linked to earlier onset of symptoms and more severe pain.
What Can Be Done to Manage This Kind of Pain?
Because central sensitization doesn’t just come from tissues, treating pain requires more than just surgery or hormones. An interdisciplinary approach tends to work best. Interdisciplinary means that your providers are working together for your benefit. This is much better than multidisciplinary, which often indicates multiple providers that are not necessarily working with one another or communicating your treatment plan for your benefit. At Femina Physical Therapy, we coordinate care with other providers wherever necessary to optimize you reaching your goals. For example:
- Physical therapy: Gentle manual therapy, stretching, joint mobilizations, foam rolling — all aimed at relaxing muscles and releasing trigger points. Also pelvic-floor PT for abdominal or pelvic muscle tightness.
- Nervous system “down-regulation”: Therapists can teach breathing exercises, relaxation techniques, and healthy bladder/bowel habits. This helps calm the over-active nervous system.
- Pain education and other therapies: Sometimes counseling, stress-reduction, mindfulness, or other supportive therapies help. Because increased stress, anxiety, or emotional strain can make central sensitization worse.
- Medication: certain medications that act on the central nervous system to help ‘turn the volume down’ may also be prescribed. Opioids are not recommended for chronic pain.
In short: when pain becomes “wired” into the nervous system, you have to treat the nervous system and surrounding myofascial structures — not just the reproductive organs or bladder, where you may feel your pain.
Why This Matters
Understanding central sensitization helps explain how endometriosis can cause long-lasting pain — even when the abnormal tissue is treated or removed.
If someone doesn’t respond to traditional endometriosis treatments, that doesn’t mean the pain isn’t real. It may mean their nervous system has changed, and to really heal, they may need therapies beyond hormone therapy or surgery.
This understanding can also help patients and clinicians take a more comprehensive, holistic approach. Treating endometriosis isn’t always just about removing tissue — sometimes it’s about helping the nervous system “rewire” itself and calm down.