Endometriosis vs PMOS (PCOS): Key Differences

If you’re experiencing symptoms like pelvic pain, irregular periods, and bloating, identifying the underlying cause is important. However, there are a number of reasons why you might be getting symptoms like these, including endometriosis and polyendocrine metabolic ovarian syndrome (PMOS, previously known as polycystic ovary syndrome, PCOS).

Despite having some similar symptoms, endometriosis and PMOS have different causes and approaches to treatment. A diagnosis from a doctor is always your best course of action. In the meantime, this guide provides information on what these conditions are, how to tell them apart and how they are diagnosed and treated.

Endometriosis and PMOS (PCOS) at a Glance

Endometriosis and PMOS are both common chronic conditions related to reproductive health and often go undiagnosed in many people they affect. Still, they are distinct in the underlying causes and main symptoms. Despite their differences, diagnosis can be challenging and they can occur together.

What is Endometriosis?

Endometriosis is a chronic inflammatory condition where tissue similar to the womb lining grows outside the womb. This extra tissue may cause inflammation, pain, scarring and adhesions (where scar tissue causes organs to stick together rather than moving freely apart from each other) and usually grows around pelvic organs. Endometriosis affects around 10% of women of reproductive age.*

It’s not clear exactly what causes endometriosis, but it may be related to immune system problems, hormones and genetics, and retrograde menstruation (where menstrual blood enters the fallopian tubes instead of leaving through the vagina). Symptoms usually include pelvic pain, painful periods, pain during or after sex, infertility and bowel and bladder problems.

What is PMOS (PCOS)?

Polyendocrine metabolic ovarian syndrome (PMOS, previously known as polycystic ovary syndrome, PCOS) is a common hormonal and metabolic (relating to how your body converts food to energy) condition. It affects around 10 to 13% of women at reproductive age and is thought to be related to genetic factors and hormone imbalances.*

PMOS usually causes period irregularities, high male hormone levels and physical changes to the ovaries, such as increased small follicles (fluid sacs) and enlarged ovaries. As a result, PMOS may affect periods, fertility, skin, hair and metabolic changes like insulin resistance, weight gain, tiredness and an increased risk of heart disease, liver disease and type 2 diabetes. 

Comparing the Symptoms of PMOS (PCOS) and Endometriosis

Although both endometriosis and PMOS can affect periods and fertility, the range of other symptoms they cause is quite different. Endometriosis mainly involves pelvic pain and pain during sex and periods, whereas PMOS causes a range of hormonal symptoms.

How Is Each Condition Diagnosed?

Despite being reproduction-related conditions and sharing some symptoms, endometriosis and PMOS are diagnosed using different methods.

Diagnosing endometriosis

There’s no single test for endometriosis. Instead, a doctor will ask about symptoms and review your medical history. Then, they may recommend examination and testing as appropriate.

Transvaginal ultrasound

This is usually the first approach a doctor would suggest to test for possible endometriosis. The image an ultrasound creates can be examined for the existence of endometriomas (endometriosis-related cysts), which are a sign of endometriosis. A normal scan does not mean there is no possible endometriosis, it may just mean that further testing is needed.

Laparoscopy

This is a kind of keyhole surgery where a thin tube with a camera is inserted through the stomach directly into the pelvic region so a surgeon can inspect it. This can provide evidence of endometriosis where other scans have not been able to. They can also take a small tissue sample to test as well.

MRI

Magnetic resonance imaging (MRI) is not routinely used to test for endometriosis, but it can be used when deep endometriosis is suspected, where the womb lining-like tissue is growing further away from where it’s typically found. It can also be used to check the extent of the condition before surgery.

Diagnosing PMOS

PMOS is usually diagnosed using a combination of assessment, blood tests and in some cases ultrasound.

For adults the ‘Rotterdam criteria’ used, which checks for 2 of 3 signs of PMOS after other possible causes have been ruled out. These include:*

• Ovulation issues – irregular or absent ovulation, usually reflected by changes to periods, lasting less than 21 days or more than 35 days or fewer than 8 bleeds a year

• Signs of increased male hormone levels – these include increased facial and body hair or blood tests that show increased testosterone, androstenedione or DHEA-S

• Physical changes to ovaries – an ultrasound image that shows the typical changes to the ovaries that occur with PMOS

Anti-Müllerian hormone (AMH) levels may be tested in place of an ultrasound but it isn’t a standalone test for PMOS.

Can You Have Both Endometriosis and PMOS (PCOS)?

Yes. These conditions are not mutually exclusive, meaning they can appear at the same time.

In cases where they do occur together, dual diagnosis can be difficult because they share some symptoms in common, like changes to periods, pelvic symptoms and reduced fertility. They do have features that help point to the presence of each though.

Having symptoms specific to one condition doesn’t mean the other one isn’t present too, though. If symptoms last despite treatment or don’t fit diagnosis of just one of the conditions, a doctor may consider the presence of the other one as well.

Can You Have Both Endometriosis and PMOS (PCOS)?

Yes. These conditions are not mutually exclusive, meaning they can appear at the same time.

In cases where they do occur together, dual diagnosis can be difficult because they share some symptoms in common, like changes to periods, pelvic symptoms and reduced fertility. They do have features that help point to the presence of each though.

Having symptoms specific to one condition doesn’t mean the other one isn’t present too, though. If symptoms last despite treatment or don’t fit diagnosis of just one of the conditions, a doctor may consider the presence of the other one as well.

Can Having PMOS (PCOS) Increase the Chance of Endometriosis?

There is evidence that these 2 conditions are likely to occur together. A study of women undergoing surgery for PMOS found that in around 8% of cases, endometriosis was discovered at the same time.*

Scientists aren’t yet clear on exactly what causes both of these conditions to be diagnosed together more often. It is suspected they may share hormonal, metabolic or genetic factors. It could also be that they are often diagnosed together because they can both be identified by examination of the ovaries, meaning it’s likely they will be diagnosed at the same time where other conditions with more distinct diagnostic methods wouldn’t be.

Is Treatment for PMOS (PCOS) and Endometriosis Different?

Yes. Despite sharing some symptoms and diagnostic methods, they are different conditions that require different treatments.

Treating endometriosis

Endometriosis treatment usually involves controlling pain and managing symptoms. It may also include controlling the hormonal causes or in some cases surgery:

• Pain relief – non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or paracetamol may be used to reduce pain

• Hormonal treatment – hormonal contraceptives like the pill or other similar medications may be used to control the period cycle which can help avoid endometriosis symptoms

• Surgery – when endometriosis is severe, affects other organs or isn’t controlled by other treatment methods the tissue can be surgically removed

• Lifestyle changes  – for treating inflammation, including balanced diet, regular exercise and behavioural support

Treating PMOS (PCOS)

PMOS treatment usually targets the reproductive, hormonal and metabolic symptoms rather than the cysts that cause it. Options can include:

• Lifestyle changes to help metabolic symptoms – this can include a balanced diet, regular exercise and other behavioural support

• Hormonal contraception – the pill or other contraceptives that use hormones can help regulate period bleeding and manage male-hormone symptoms

• Medications for insulin resistance – diabetic medications like metformin can help where metabolic symptoms need managing, including those who are overweight or have uncontrolled blood sugar

What about GLP-1 medications?

GLP-1 receptor agonists, like weight loss injections and certain pills, are not PMOS-specific treatments. International guidelines suggest that weight loss medications can be considered alongside diet and exercise for people with PMOS who are overweight.*

GLP-1 medications have been shown to reduce inflammation, which may help with endometriosis or PMOS-related inflammation.** They can help support weight loss, and losing weight can in turn help improve some PMOS symptoms, such as irregular periods.

FAQs

Can endometriosis be mistaken for PMOS?

Yes. Due to the fact that they share some symptoms, it is possible that one condition can be mistaken for the other. Although they do have distinguishing features, they can be confused for one another or one may be missed if they occur together. Further examination and testing can help if treatment doesn’t improve symptoms after a misdiagnosis.

Which is more painful, endometriosis or PMOS?

Endometriosis is usually linked to ongoing and sometimes severe pain. PMOS is not associated with pain to the same extent, although pain can still be a symptom in some cases. How painful endometriosis is depends on the individual person and their symptoms and whether they’re receiving treatment.

Is it harder to conceive with endometriosis or PMOS?

It varies. Both can affect fertility, but the extent of the effects depend on how severe the conditions and symptoms are. Having either or both conditions doesn’t necessarily mean pregnancy isn’t possible. Treatment for the condition or to support fertility can help.

Does PMOS ever fully go away?

PMOS is considered a chronic condition, so it doesn’t normally fully go away. However, the extent of the symptoms can change over time and may be controlled completely with appropriate treatment.

Is PMOS or endometriosis more common?

Both are roughly as common as one another. Endometriosis affects around 10% of women of reproductive age* and PMOS affects between 10 and 13%⁺, so PMOS might be slightly more common. These statistics are only estimates as exact numbers are not clear due to how many people remain undiagnosed.