There Are 4 Stages of Endometriosis. Here's What Each One Means

Experts use stages to classify endometriosis by severity, but the stage doesn't always correspond to a woman's pain and discomfort levels.

Endometriosis is a condition in which endometrial tissue that lines the uterus begins to spread outside of the uterus and implant in places like the fallopian tubes, ovaries, and other organs in the pelvic region.

When it grows normally inside the uterus, endometrial tissue sheds during every menstrual cycle, creating a monthly period. But endometrial tissue also sheds when implanted or attached to organs outside of the uterus, and this shedding can cause inflammation, cysts, and scar tissue throughout the pelvic region.

Women with endometriosis may experience symptoms like chronic pelvic pain, pain during sex, painful urination, gastrointestinal issues, abnormal or heavy periods, and infertility.

What happens after an endometriosis diagnosis?

An estimated one in 10 women has endometriosis, but it can take anywhere from three to 11 years for them to be officially diagnosed with the condition once their symptoms start.

Because the painful symptoms could be caused by a wide variety of other health conditions, doctors in the past have generally preferred to make their diagnosis by exclusion. When they suspect endometriosis, it's confirmed visually with a procedure called a laparoscopy, although this reliance on surgical diagnosis is slowly changing.

During a laparoscopy, the doctor makes a small incision in the abdomen and inserts a thin tube with a light and camera to view the pelvic region. If they see signs of endometriosis, like implanted endometrial tissue or scar tissue, they can both diagnose the condition and remove things like cysts and scar tissue.

Being able to see endometriosis implants and scarring is what enables doctors to classify the disease into four different stages. To determine the stage of endometriosis, doctors assign points to what they see as they perform the laparoscopy. A score of 15 or less means that the disease, visually, is either Stage 1 (minimal) or Stage 2 (mild). A score of 16 to 40 means the disease is Stage 3 (moderate), and 40 or more puts the disease at Stage 4 (severe).

What the endometriosis stages mean

Based on what the doctor sees during the laparoscopy, the endometriosis is categorized into four different stages.

Stage 1 (1 to 5 points)
In Stage 1, the endometriosis is considered “minimal.” The implants are small, few in number, and shallow, although keep in mind that these stages don’t correspond to pain and discomfort levels (more on that later). Just because a woman might have Stage 1 endometriosis, this doesn’t mean that her pain is minimal or that the effect on her life has been minimal.

Stage 2 (6 to 15 points)
In Stage 2, the endometriosis is considered “mild.” Doctors might find more implants, and they are deeper than the superficial implants found in Stage 1 endometriosis.

Stage 3 (16 to 40 points)
Stage 3 is “moderate” endometriosis. Not only are there many deep endometrial implants, but there may be endometrial cysts on at least one ovary. These endometrial cysts form when the tissue attaches to an ovary and begins to shed blood and tissue. The blood collects and turns brown, which is why these growths are also known as “chocolate cysts.”

Doctors may also find thin bands of tissue, called filmy adhesions, that bind organs together. These adhesions are the scar tissue that form when the body tries to heal from the inflammation caused by endometriosis. They can make organs stick together when they shouldn’t and are thought to be the cause of sharp, stabbing pains, as well as nausea, in women with endometriosis.

Stage 4 (40 or more points)
Stage 4 is the “severe” stage of endometriosis. In addition to many deep endometriosis implants, there are large cysts on at least one ovary and many dense adhesions throughout the pelvic region.

What the stages don't mean

The escalating severity of these stages might give the impression that endometriosis, like cancer, first starts off in one part of the body before spreading to more distant organs.

But endometriosis doesn’t grow like a cancer, as the disease can be widespread from the beginning, Hugh Taylor, MD, vice president of the American Society for Reproductive Medicine and chair of obstetrics, gynecology, and reproductive science at Yale School of Medicine, tells Health.

“If you want to say someone is better or worse after some kind of treatment or surgery, or if you want to compare one surgery to another, you really need a system and formula in place to act like some kind of quantitative comparison,” Dr. Taylor says about the stages. “But this is not the same type of staging system that would have meaningful prognostic value like in a cancer.”

For instance, endometriosis stages don’t correlate to how badly things like infertility or chronic pain affect a woman. This also means that the stages don’t necessarily give guidance on how to treat endometriosis for different patients.

“Patients like to know how widespread it was,” Dr. Taylor says. “But someone with minimal to mild endometriosis can have more pain than someone with severe endometriosis.” Alternately, a woman with Stage 1 endometriosis might be more infertile than a woman with Stage 4 endometriosis, he adds.

Because of the difficulty in describing endometriosis in a way that is meaningful for treatment, others have tried to propose different ways to classify the disease.

The Endometriosis Foundation of America, for instance, has divided up the disease into four categories depending on where the disease is located and how it affects the patient:

Category 1: Peritoneal endometriosis
The endometriosis is located on the peritoneum, which is a membrane that lines the abdomen. This is the most minimal category.

Category 2: Ovarian endometriomas
There are endometriomas, or cysts, in the ovaries, which pose the risk of bursting and spreading the endometriosis to other nearby organs.

Category 3: Deep infiltrating endometriosis 1
The endometriosis has implanted in organs in the pelvic region, like the ovaries, rectum, and the outside of the uterus. The patient may be experiencing “frozen pelvis,” which is when scar tissue binds organs together and impairs their function.

Category 4: Deep infiltrating endometriosis 2
The endometriosis is present outside the pelvic region as well and may have implanted in distant organs like the heart, lung, and brain.

Raising awareness is key to better endometriosis treatment

In an effort to cut down on the time it takes to diagnose and treat endometriosis, there is a movement among doctors to start recognizing the signs of the disease clinically, without the need for surgery, Dr. Taylor says.

One classic sign of endometriosis is painful periods, which then progress to pain that lasts beyond the menstrual cycle. Sometimes, physical exams can reveal cysts, and other times ultrasounds can reveal that organs like the uterus might be pulled or tilted toward a certain side—a sign that scar tissue has formed.

“The first thing I always hear from endometriosis patients is that they complain about the pain, and their mother, friends, and even their physicians, say, ‘Oh, periods are supposed to hurt, that’s normal,’” Dr. Taylor says. “It’s not until they really start to get disrupted, like missing school or work, that people start taking it seriously.”

Taking a woman’s pain seriously could save her years of frustrating misdiagnoses, Dr. Taylor says. It could also curb symptoms sooner, which could cut down on the development of painful and debilitating scar tissue.

If a woman is diagnosed with endometriosis, treatment will depend on both her symptoms and her goals. Birth control pills might control the pain for some mild cases; if a woman’s primary concern is her infertility, in vitro fertilization may be the best treatment.

Other drugs that affect hormone levels can be effective, although some come with severe side effects. Lupron, an injectable drug, brings the level of estrogen down so low that it could cause young women to enter early menopause. Danazol uses male hormones to control endometriosis but may cause hair growth or acne.

“Surgery can be a treatment, I think it’s a treatment—but of last resort,” Dr. Taylor says. “It’s about getting people treated earlier before [endometriosis] really disrupts their lives.”

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