Endometriosis

What it is

Endometriosis is a chronic, estrogen-dependent inflammatory condition affecting an estimated 10% of women of reproductive age — approximately 190 million people worldwide — in which tissue resembling the endometrium grows outside the uterus. Also called endometrial-like tissue disease, it is one of the leading causes of chronic pelvic pain and infertility. Despite its prevalence, the average time from first symptoms to confirmed diagnosis is 7 to 10 years, a delay that carries real consequences for pain management and fertility preservation.

In Canada, endometriosis affects an estimated 1 in 10 women of reproductive age. The Society of Obstetricians and Gynaecologists of Canada (SOGC) has identified diagnostic delay as a priority concern, and Canadian gynaecologists increasingly use non-surgical imaging alongside clinical history to shorten the path to diagnosis.

The misplaced tissue behaves like normal endometrium: it responds to the hormonal cycle, builds up, and attempts to shed with each period. Because it has no exit route, it triggers local inflammation, scar tissue (adhesions), and — when lesions form on the ovaries — blood-filled cysts called endometriomas.

Causes and mechanism

The exact cause of endometriosis is not fully understood, but several mechanisms are well-supported:

• Retrograde menstruation is the most widely accepted theory. During menstruation, blood flows backward through the fallopian tubes into the pelvis, seeding endometrial cells. In women with endometriosis, these cells implant and grow — likely because immune clearance is impaired.
• Immune dysfunction appears central: women with endometriosis show a reduced peritoneal immune response that fails to eliminate retrograde cells.
• Estrogen dependency sustains the disease. Endometriotic lesions express aromatase, the enzyme that converts androgens to estrogen locally, creating a self-reinforcing hormonal environment that promotes lesion survival.
• Inflammatory signalling — via prostaglandins and cytokines released by lesions — perpetuates both pain and tissue growth.

Recognized risk factors include early onset of menstruation, menstrual cycles shorter than 28 days, heavy or prolonged periods, a first-degree family history of endometriosis, and structural abnormalities that impair menstrual outflow.

Symptoms and diagnosis

Symptom severity does not reliably reflect disease extent. Some women with widespread endometriosis have minimal pain; others with limited disease have debilitating symptoms. This disconnect is a key reason diagnosis is so often delayed.

Common symptoms:

• Dysmenorrhoea (painful periods) that typically begins before menstruation and persists throughout
• Chronic pelvic pain outside of menstruation
• Dyspareunia (deep pain during intercourse)
• Painful bowel movements or urination, particularly around the period
• Heavy or irregular menstrual bleeding
• Bloating, nausea, and fatigue
• Infertility: approximately 30–50% of women with endometriosis experience fertility difficulties

Diagnostic pathway:

Step	Method	Notes
1	Clinical history	Cyclical pain patterns, symptom duration
2	Pelvic ultrasound	Identifies endometriomas; operator-dependent for deep disease
3	MRI	Better mapping of deep infiltrating endometriosis
4	Laparoscopy + biopsy	Gold standard; confirms diagnosis histologically

In Canada, pelvic ultrasound is widely available through LifeLabs and Dynacare requisitions, and MRI is accessible via provincial health plans, though wait times vary by province.

Treatment options

There is no cure for endometriosis, but symptoms and disease progression can be managed effectively with hormonal therapy, surgery, or a combination of both.

Hormonal treatments:

• Combined oral contraceptives suppress ovulation and reduce lesion activity; typically first-line.
• Progestogens (norethisterone, dienogest, depot medroxyprogesterone) suppress endometrial tissue growth.
• GnRH agonists (leuprolide, goserelin) induce a temporary menopause-like state; effective for pain but carry bone density risk with prolonged use, so add-back low-dose hormone therapy is standard.
• GnRH antagonists (elagolix) suppress estrogen more gradually with a somewhat better tolerability profile; approved in Canada under the brand name Orilissa.
• Levonorgestrel IUD (Mirena) significantly reduces pain and bleeding and is covered under most provincial drug benefit programs.

Surgical management:

• Laparoscopic excision removes lesions and adhesions; excision is generally preferred over ablation because it addresses deeper disease.
• Hysterectomy is reserved for severe, refractory cases in women who have completed their family.

For fertility:

• Surgical removal of lesions may improve natural conception rates in mild-to-moderate disease.
• IVF is recommended for moderate-to-severe endometriosis with infertility.

Adjunct pain management:

• NSAIDs for symptomatic relief
• Pelvic floor physiotherapy
• Multidisciplinary pain programs

Canadian patients can discuss hormonal options with their GP, a gynaecologist, or through virtual care platforms (Felix, Maple, Cleo, Phoenix, and others) that can initiate or bridge prescriptions pending specialist referral.

When to see a clinician in Canada

See a clinician if period pain is severe enough to disrupt work, school, or daily activities, or if pain has worsened progressively over time. Severe dysmenorrhoea is not a normal part of menstruation and should not be dismissed as such.

Also seek evaluation for: chronic pelvic pain outside your period; deep pain during sex; pain with bowel movements around menstruation; or difficulty conceiving after 6–12 months of unprotected intercourse (6 months if you are over 35).

Given the average 7–10 year diagnostic delay, early referral to a gynaecologist with endometriosis experience — or to a dedicated endometriosis centre where available — is worthwhile if symptoms are recurring and affecting quality of life.

Limitations and open questions

Research is still emerging on several fronts. The precise interplay between immune dysfunction and retrograde menstruation remains incompletely understood, and no blood-based biomarker has yet been validated for non-surgical diagnosis — though several are in clinical trials. The long-term recurrence risk after excision surgery varies widely across studies (20–40% at 5 years), and optimal post-surgical hormonal regimens have not been settled by randomized trials of sufficient size.

Health Canada has not yet issued a standalone clinical guideline on endometriosis management; Canadian clinicians currently rely on SOGC position statements, ESHRE guidelines, and ACOG practice bulletins, which do not always align on first-line treatment sequencing. The role of diet, microbiome, and environmental estrogen exposure in disease onset and progression is an active area of investigation, but evidence is not yet sufficient to make firm clinical recommendations.