Ectopic Endometrial Lesions Trigger Local Inflammation
Misplaced tissue outside the uterus ignites a chronic immune response.
- ~10%: Prevalence (reproductive-age women)
- ~7 yrs: Diagnostic delay (average time to diagnosis)
- Ovary, peritoneum: Common sites (pelvic implants)
- 10×: Peak macrophages (vs normal peritoneal fluid)
What are ectopic implants
Endometrial-like tissue grows outside the uterine cavity.
Local immune reaction
Macrophages and mast cells swarm and release cytokines.
Prostaglandin surge
Lesions overproduce PGE2, fueling pain and lesion growth.
Neurogenic Inflammation Sensitizes Pelvic Nerves
Inflammatory mediators lower the firing threshold of local nerves.
- ↑ 2-3×: Nerve fiber density (in lesion-adjacent tissue)
- NGF: Key mediator (nerve growth factor)
- Histamine: Mast cell role (sensitizes nociceptors)
- C & Aδ: Fiber types affected (pain-conducting fibers)
Mediator cascade
Cytokines, NGF, and prostaglandins bathe nearby nerve endings.
Nerve fiber sprouting
New nerve fibers grow directly into lesion tissue.
Lowered pain threshold
Sensitized nociceptors fire from normally painless stimuli.
Sensitized Nerves Fire More Readily
Chronic peripheral input keeps pain pathways continuously active.
- Weeks: Allodynia onset (after sensitization begins)
- ↑ markedly: Signal frequency (in sensitized fibers)
- >6 mo: Pain chronicity (defines chronic pelvic pain)
- ~80%: Dysmenorrhea link (of patients affected)
Peripheral sensitization
Nociceptors lower their activation threshold repeatedly.
Signal amplification
Repeated firing strengthens the pain pathway itself.
Chronic pain onset
Pain persists even between menstrual cycles.
Spinal Cord Neurons Become Hyperexcitable
Prolonged input rewires spinal pain-processing circuits.
- NMDA: Wind-up phenomenon (receptor-driven amplification)
- Widened: Pain spread (beyond pelvic dermatome)
- Positive: Duration correlation (longer disease, more sensitized)
- IBS, IC: Comorbid conditions (often co-occur)
Dorsal horn changes
Spinal neurons amplify incoming pain signals.
Wind-up and NMDA
Repeated firing recruits NMDA receptors, boosting response.
Widespread pain
Pain can spread beyond the original pelvic site.
Targeting Multiple Pain Pathways at Once
NSAIDs, progestins, and adjuncts each interrupt a different step.
- COX-1/2: NSAID target (blocks prostaglandin synthesis)
- Lesion activity: Progestin target (suppresses growth & bleeding)
- Highest: Combined efficacy (multi-pathway coverage)
- PT, neuromodulators: Adjunct options (address central sensitization)
NSAIDs block prostaglandins
COX inhibition reduces peripheral inflammatory pain.
Progestins suppress lesions
Hormonal therapy shrinks lesion activity at the source.
Combined multimodal care
Layered therapy addresses peripheral and central pain.