What is endometriosis?

Definition and prevalence

Endometriosis is a gynecological condition that affects approximately 10 % of the female population. It occurs when cells similar to the ones that make up the uterine lining (the endometrium) grow outside of the uterus, most often on other organs in the pelvis and the abdominal cavity. This misplaced endometrial tissue acts just like the endometrium and reacts to the hormonal changes that occur during the menstrual cycle. It thickens and bleeds, and since the blood has nowhere to go, this causes swelling, inflammation and scarring in the surrounding tissue. In some cases, the scar tissue binds different types of tissue together, forming adhesions.

Locations

Endometriosis is most commonly found on:

the ovaries
the fallopian tubes
the pelvic peritoneum (the lining of the abdominal cavity)
the uterosacral ligaments (the fibrous tissue and muscular fibers that support the uterus)
the outer surface of the uterus
the posterior cul-de-sac (the space between the uterus and the rectum)
the anterior cul-de-sac (the space between the uterus and the bladder)

Occasionally, it can be found in other places, such as:

the bowels (the small bowel, large bowel, rectum, and appendix)
the urinary tract (the bladder, kidneys, ureters, and the urethra)
the thoracic cavity, breast, chest and lungs
the cervix, vagina, and vulva
the umbilical region
the inguinal region (the groin)
the liver, gallbladder, and pancreas
the pelvic nerves

In fact, the only place where endometriosis hasn't been found is the spleen.

Causes

The exact cause of endometriosis hasn't been established yet, but there are several theories about how it occurs. The most common theory is retrograde menstruation. This means that the menstrual blood, which contains endometrial cells, flows back through the fallopian tubes and into the pelvic cavity instead of out of the body. These cells then stick to different surfaces and organs, where they continue to grow and follow the course of the menstrual cycle.

However, retrograde menstruation is actually a normal process that occurs in most women, and not all of them develop endometriosis. It is thought that the reason for this is that the immune system usually removes the displaced endometrial tissue. In some women, however, the immune system seems unable to recognize and destroy it, thus causing endometriosis.

Other theories have different explanations:

Certain hormones or immune factors may promote the transformation of peritoneal cells (cells that line the inner side of the abdomen) into endometrial cells.
Hormones such as estrogen may turn embryonic cells into endometrial cells during puberty.
Endometrial cells may attach to a surgical incision after abdominal surgery (e.g. C-sections).
The blood vessels and/or lymphatic system may transport endometrial cells from the uterus to other parts of the body.

Stages

There are four stages of endometriosis, ranging from minimal (stage 1) to severe (stage 4). There are several different factors that determine the stage of the condition, e.g. the location, amount, depth, size and spread of the endometrial implants, and the presence and severity of scar tissue and adhesions. If you suffer from endometriosis, you can have anything from just a few isolated and shallow implants to multiple deep implants in different parts of your body and thick adhesions that cause several tissues and organs to stick together.

It's important to understand that the stage of the endometriosis doesn't necessarily reflect the level of pain or symptoms experienced. Someone with minimal endometriosis can suffer from severe pain and a huge amount of different symptoms while someone with stage 3 or 4 can be completely asymptomatic.

Symptoms

Endometriosis can cause a large amount of different symptoms. Unfortunately, a lot of people (including healthcare professionals) still only associate it with gynecological symptoms, especially period pain (dysmenorrhea). Other symptoms are often overlooked, disregarded, or blamed on other physical conditions, stress, and even mental health issues. Not only is this incredibly frustrating, but it also delays the diagnose and treatment.

The most common symptoms of endometriosis are:

Pelvic, abdominal, and lower back pain that often gets worse during menstruation and/or ovulation
Pain in the legs, hips, and buttocks (often caused by endometriosis growths that impact the nerves surrounding the pelvis)
Pain during or after intercourse, especially during deep penetration
Heavy menstrual periods and/or bleeding between periods, irregular menstrual cycle
Bloating, nausea, vomiting
Constipation, diarrhea, abdominal cramping, rectal bleeding, and pain with bowel movements. These symptoms are sometimes caused by bowel endometriosis, but it is far more common that they are caused by the inflammation in the abdominal cavity, or by the activation of the sympathetic nervous system.
Urinary pain and/or UTI symptoms such as feeling the need to urinate frequently, a burning or painful sensation when you when urinating, pain when the bladder is full, blood in the urine (hematuria)
Fatigue (can be caused by the inflammation that occurs due to the endometriosis)
Joint pain and/or generalized body pain (because of the inflammation)
Infertility

Many of these symptoms often occur or get worse during a woman's menstrual period, which can raise suspicion that they are caused by endometriosis. However, it's important to remember that this is not always the case and that you can still suffer from endometriosis even if your symptoms don't seem to be related to your menstrual cycle.

Why does endometriosis cause pain?

Not everyone with endometriosis experiences pain, but for those who do, the pain can be debilitating. There are several reasons why this happens.

The displaced endometrial tissue that grows outside of the uterus follows the menstrual cycle, i.e. it thickens, breaks down, and bleeds. Since the blood doesn't have a way to exit the body, it becomes trapped and causes irritation and inflammation in the surrounding tissue - especially during menstruation. The endometrial cells and the swelling (caused by the inflammation) trigger nerve endings that send pain signals to the brain. The inflammation itself can also cause pain, e.g. in the joints.

With time, scar tissue may develop. In some cases, it causes different tissues and organs to stick together, sort of like glue. These fibrous bands (the "glue") are called adhesions and can cause pain, for instance by limiting the movement or function of the organs and tissues that they are stuck to. For example, adhesions on the bladder or the urethra may cause pain when urinating, and bowel adhesions that partially block the intestines can cause stomach cramps. They can also cause pain by squeezing or pulling on nerves and organs (imagine two organs stuck together with a nerve in between). In some cases this pain occurs when you do certain movements or when you sit/lie in a certain position.

Co-occurring conditions

According to several studies, many conditions seem to occur more often in women with endometriosis than others. These include:

Uterine fibroids
Interstitial cystitis
Hypothyroidism
Rheumatoid artritis
Celiac disease
Fibromyalgia
Multiple sclerosis (MS)
Systemic lupus
Vaginal infections
Upper respiratory infections
Pelvic inflammatory disease
Irritable bowel syndrome (IBS)
Cardiovascular diseases
Ovarian cancer
Skin cancer
Depression
Anxiety
Asthma, allergies, eczema, and food sensitivities
Irritable bowel disease (IBD) such as Crohn's disease and ulcerative colitis

We still don't know a lot about this, but there are a few possible explanations:

Some of the causes or risk factors for developing endometriosis may be the same as for other conditions, e.g. abnormal immune system responses and oxidative stress.
Endometriosis may induce physical changes that increase the risk of developing other diseases. These changes include chronic inflammation, hormonal or immunologic responses, and lifestyle changes.
Treatment(s) for endometriosis may be associated with or increase the risk of developing certain diseases.

How much period pain is normal?

Even though menstruation is the most natural thing in the world and something that pretty much all women experience, it's a topic that is often considered embarrassing and that a lot of people don't really want to talk about. When young girls grow up around adults with this attitude, they have no idea what to expect when they get their first period. They don't know what is normal and what isn't, and are often too embarrassed to ask. There is also a common misconception that period pain is normal, that all women experience it, and that you just have to suck it up and deal with it.

If you experience any of the following, you may want to consider seeking help.

You still have severe pain despite taking over-the-counter painkillers (such as paracetamol and NSAIDs).
You often have to stay home from school or work when you have your period.
The pain affects your everyday life.
You have trouble sleeping because of the pain.
Your period is so heavy that you have to wear large pads and tampons at the same time, or you have to change pads/tampons every 1-2 hours.
You have to get up in the middle of the night to change pads/tampons.
You experience dizziness, nausea and/or vomiting, or feel very weak.
You have period pain in other body parts than your stomach or lower back, e.g. in your legs.
You have trouble urinating and/or passing stool.
You have painful bowel movements and/or pain when urinating.
There is blood in your urine or feces.