Causes and Symptoms of Endometriosis

Introduction

Endometriosis is a chronic inflammatory gynecologic condition where endometrial-like tissue (a tissue similar to the lining of the uterus) grows outside the uterus, causing pain and sometimes fertility problems. It can affect various parts of the body, including the pelvic area, ovaries, intestines, and bladder. Sometimes, it can even affect other organs like the lungs or heart lining.^1,2,3

It's estimated to affect about 10-15% of people assigned female at birth (AFAB)of reproductive age, but this number can be higher, especially among those with chronic pelvic pain. Many people with AFAB may have endometriosis without knowing because they don't show symptoms and it's hard to know exactly how many have it because it is difficult to diagnose.^1,2

Studies have found that people AFAB with endometriosis lesions may have a greater likelihood of developing ovarian and breast cancer, melanoma, asthma, rheumatoid arthritis, and cardiovascular disease.²

Causes of endometriosis

Several theories have been developed to explain the cause of endometriosis, linking the severity of symptoms to the stage of the disease. However, none of these theories can fully account for all the different ways the disease presents clinically.¹

Retrograde menstruation

The leading theory, known as Sampson's theory, suggests that during menstruation, some cells from the lining of the uterus flow backwards through the Fallopian tubes and into the abdomen. These cells can stick to organs there and grow, causing endometriosis. This backward flow of menstrual blood, called retrograde menstruation, happens in many people AFAB and is thought to be a common occurrence.^1,2 Furthermore, young people who have certain conditions where the reproductive tract is blocked or shaped differently, are more likely to develop endometriosis.⁴

Although this is a well-known theory, it only partially explains some cases of the condition. It explains endometriosis in certain areas, like the ovaries or the surface of organs in the abdomen, but not for deeper lesions or those outside the abdomen. Moreover, many people AFAB experience retrograde menstruation without developing endometriosis. Some other factors might play a role.^4,5

Coelomic metaplasia

Another theory besides Sampson's is the coelomic metaplastic theory, by Meyer. It suggests that some cells in the abdomen can transform into endometrial tissue under the influence of certain chemicals in the body. This might explain why some people without a uterus, like those with Mayer-Rokitansky-Küster-Hauser syndrome, or even rare cases of people assigned male at birth (AMAB) with endometriosis, after receiving estrogen treatment for prostate cancer, can still develop the condition.^4,5

Benign metastasis

Another idea proposed by Sampson is called the theory of benign metastasis. This theory suggests that during menstruation, a small amount of tissue from the endometrial tissue can travel through lymphatic vessels, which are tiny tubes in the body, to other parts of the body. This might explain why endometriosis can be found in places like the lymph nodes or even the lungs.⁵

Research has shown that people AFAB with endometriosis have changes in the expression of certain proteins that promote the growth of lymphatic vessels in the uterus. These changes might make it easier for endometrial tissue to travel through the lymphatic system. However, it's still not fully understood how these changes contribute to the development of endometriosis.⁵

Embryonic cell transformation

Another theory suggests that endometrial‐like tissue might be leftover from when a person was developing as an embryo, specifically from certain ducts. These misplaced cells might stay inactive in the pelvic area until puberty when they're exposed to hormones like oestrogen.^4,5

Immune system disorders

The body's immune system may play a role in endometriosis. Cells from the immune system, found in both the lining of the uterus and the surrounding area in the abdomen, are thought to contribute to the development of the disease. Studies have shown that specific types of immune cells called macrophages are more abundant in the endometrium during different stages of the menstrual cycle in people with endometriosis than those without. This suggests that these cells might be involved in the formation and growth of endometrial lesions.⁴

Also, inflammation caused by immune system problems could be a major factor. Inflammation stops the body's natural process of getting rid of harmful cells, allowing them to stick to different parts of the body. Various types of immune cells, including macrophages, neutrophils, natural killer cells, dendritic cells, and T cells, may be involved in the formation and growth of endometrial lesions.⁵

Symptoms of endometriosis

Endometriosis can present differently among people AFAB, and it might take a while for doctors to understand what's going on. People with endometriosis often have symptoms like:^1,2,3

• Painful sex 
• Pelvic pain during periods 
• Pain when urinating or having a bowel movement
• Trouble getting pregnant
• Fatigue and depression

Endometriosis can cause different levels of pain in distinct people, ranging from occasional discomfort to constant and severe pain that affects their daily lives. The pain can be constant, getting worse over time, and some people might even feel severe pain from non-painful things, which could be a sign of nerve-related pain. Interestingly, the severity of endometriosis doesn't always match up with how much pain someone feels.^1,2

Diagnosis 

It often takes a long time for doctors to diagnose endometriosis, usually taking 4 to 11 years after symptoms begin. This delay happens because there isn't a specific test to confirm the disease, and the symptoms can be similar to other conditions.^1,2,3 The methods by which endometriosis is typically diagnosed are as follows:

• Doctors start by asking about symptoms and doing a physical exam, which might show signs like tender areas or lumps in the pelvis, but sometimes, there aren't any visible signs
• Imaging tests might be helpful but they might not always show the problem clearly, especially for milder cases:
  • Ultrasound - good for finding certain types of endometriosis, especially in the ovaries
  • Magnetic resonance imaging (MRI)  - helps visualise deeper areas
• Laparoscopy is a surgical procedure often needed for a definite diagnosis, where doctors look inside the pelvis to see if there are any signs of endometriosis and may take a sample for testing to confirm the diagnosis 

However, even with surgery, it's not always easy to diagnose endometriosis, especially in younger people with AFAB.

Treatment Options

Medication 

There isn't a specific drug to cure endometriosis, but medicines can help manage symptoms and improve fertility rates. The first-line treatment usually includes drugs like pain relievers, hormonal contraceptives, or progestins. These can help by reducing inflammation and pain or by changing hormone levels to control symptoms. Although, they might cause side effects like weight gain or acne.^1,2,3

Surgical intervention

Surgery is another option, especially for severe cases or if medicines don't work. It can relieve pain and improve fertility by removing endometriosis lesions and scar tissue. However, surgery also has risks as it may affect ovarian function, and many people with AFAB need more surgery later on. The choice of treatment depends on factors like the severity of symptoms, fertility desires, and potential risks.^1,2,3

Lifestyle changes and other therapies

Besides surgery and medication, options like dietary changes, physiotherapy, and psychology can help manage symptoms. Dietary changes and supplements like omega-3 fatty acids might reduce inflammation, while pelvic physiotherapy and cognitive behavioural therapy can teach coping strategies for pain. It's important to consider these non-drug options alongside medical treatment for a personalised approach to managing endometriosis pain.³

Summary 

Endometriosis is a chronic inflammatory condition where tissue similar to the lining of the uterus grows outside the uterus, often causing pain and sometimes fertility issues. It affects about 10-15% of people AFAB of reproductive age. Several theories attempt to explain its cause, including retrograde menstruation, coelomic metaplasia, benign metastasis, embryonic cell transformation, and immune system disorders.

Symptoms vary among people with AFAB and range from pelvic pain during menstruation to painful sex and difficulty conceiving. Diagnosis is challenging and can take several years due to the lack of a definitive test and symptoms overlapping with other conditions, it typically involves physical exams, imaging tests, and sometimes laparoscopy. Treatment options aim to manage symptoms and may include medication like pain relievers and hormonal contraceptives, surgery to remove lesions and scar tissue, and lifestyle changes such as dietary adjustments and physiotherapy. An individual approach considering symptom severity, fertility desires, and potential risks guides treatment decisions.