The endometrium is the tissue that lines the inside of the womb (uterus). Endometriosis is a condition where tissue similar to endometrial tissue is found outside the uterus. It is 'trapped' in the pelvic area and lower tummy (abdomen) and, rarely, in other areas in the body.
Currently it is not known what causes endometriosis. There are many responsible factors, possibly including genetic, immunological and hormonal reasons.
The exact number of women who develop endometriosis is not known. This is because many women have endometriosis without symptoms, or with mild symptoms, and are never diagnosed.
Investigations to diagnose endometriosis are only done if symptoms become troublesome and are not eased by initial treatments (see below). Estimates vary, so that from about 1 in 10 to as many as 5 in 10 of all women develop some degree of endometriosis.
If symptoms develop they typically begin between the ages of 25-40. Sometimes symptoms begin in the teenage years. Endometriosis can affect any woman. However:
- Sometimes it runs in families. Therefore, endometriosis is more common in close blood relatives of affected women.
- Endometriosis is rare in women past the menopause, as to develop endometriosis you need oestrogen, the female hormone. Oestrogen levels fall after the menopause.
- The combined oral contraceptive pill (often called 'the pill') reduces the risk of developing endometriosis. This protective effect may persist for up to a year after stopping 'the pill'.
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Patches of endometriosis can vary in size from the size of a pinhead to large clumps. Many women with endometriosis have no symptoms. If symptoms develop they can vary, and include those listed below.
In general, the bigger the patches of endometriosis, the worse the symptoms. However, this is not always the case. Some women have large patches of endometriosis with no symptoms. Some women have just a few spots of endometriosis but have bad symptoms. There are many different possible symptoms. More common symptoms include:
- Painful periods. The pain typically begins a few days before the period and usually lasts the whole of the period. It is different to normal period pain which is usually not as severe and doesn't last as long.
- Painful sex. The pain is typically felt deep inside and may last a few hours after sex.
- Pain in the lower tummy (abdomen) and pelvic area. Sometimes the pain is constant but it is usually worse on the days just before and during a period.
- Other menstrual symptoms may occur - for example, bleeding in between periods.
- Difficulty becoming pregnant (reduced fertility). This may be due to clumps of endometriosis blocking the passage of the egg from an ovary to the Fallopian tube. Sometimes, the reason for reduced fertility is not clear.
- Other symptoms include fatigue, pain on passing poo (faeces), pain in the lower abdomen when you pass urine, low back pain and, rarely, blood in the urine or faeces.
- Very rarely, patches of endometriosis occur in other sites of the body. This can cause unusual pains in parts of the body that occur at the same time as period pains.
There have been several theories over the years. The lining of the womb (uterus) is called the endometrium. One theory was that some cells from the endometrium get outside the uterus into the pelvic area. They get there by spilling backwards along the Fallopian tubes when you have a period.
Patches of endometriosis tend to be 'sticky' and may join organs to each other. The medical term for this is adhesions. For example, the bladder or bowel may 'stick' to the uterus. Large patches of endometriosis may form into cysts which bleed each month when you have a period. The cysts can fill with dark blood and are known as 'chocolate cysts'.
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How is the diagnosis of endometriosis confirmed?
The symptoms caused by endometriosis can be caused by other conditions. Therefore, if any of the above symptoms become persistent then tests are usually advised to find the cause of the symptoms. Endometriosis is usually confirmed by a laparoscopy. This is a small operation which involves making a small cut, under anaesthetic, in the tummy (abdominal) wall below the tummy button (umbilicus). A thin telescope-like instrument (a laparoscope) is pushed through the skin to look inside. Patches of endometriosis can be seen by the doctor.
How does endometriosis progress?
How your endometriosis progresses is very variable. If endometriosis is left untreated, it may improve but may also get worse or stay the same. Endometriosis is not a cancerous condition.
Complications sometimes occur in women with severe untreated endometriosis. For example, large patches of endometriosis can sometimes cause a blockage (obstruction) of the bowel or of the tube (the ureter) from the kidney to the bladder.
What are the aims of treatment?
The main aims of treatment are to improve symptoms such as pain and heavy periods and to improve fertility if this is affected. There are various treatment options which are discussed below.
If symptoms are mild and fertility is not an issue for you then you may not want any treatment. In about 3 in 10 cases, endometriosis clears and symptoms go without any treatment. You can always change your mind and opt for treatment if symptoms do not go, or become worse.
Painkillers for endometriosis
- Paracetamol taken during periods may be all that you need if symptoms are mild.
- Anti-inflammatory painkillers such as ibuprofen, diclofenac, and naproxen, may be better than paracetamol. However, some people have side-effects with these.
- Codeine alone, or combined with paracetamol, is a more powerful painkiller. It may be an option if anti-inflammatories don't suit. Constipation is a common side-effect.
To ease pain during periods, it is best to take painkillers regularly over the time of your period rather than 'now and then'. You can take painkillers in addition to other treatments.
Hormone treatments for endometriosis
There are several options. They can be effective, particularly in reducing pain. They do not improve fertility but there is no permanent reduction in fertility.
- The combined oral contraceptive pill - 'the pill'.
- The intrauterine system (IUS).
- Gonadotrophin-releasing hormone (GnRH) analogues. There are several GnRH analogue preparations which include buserelin, goserelin, nafarelin, leuprorelin and triptorelin.
- Progestogen hormone tablets. Progestogen hormone tablets include norethisterone, dydrogesterone and medroxyprogesterone.
Sometimes an operation is advised to remove some of the larger patches of endometriosis. An operation may ease symptoms, and increase the chance of pregnancy if infertility is a problem.
There are various techniques that can be used. Most commonly, a thin telescope-like instrument (a laparoscope) is pushed through a small cut in the tummy (abdomen). The surgeon then uses the laparoscope to see inside the abdomen and remove any cysts or other endometriosis tissue (keyhole surgery).
An alternative to excision (removal of areas of endometriosis) is to use direct heat or a laser to destroy the suspected endometriosis tissue (this is called ablation). Excision is now preferred to ablation.
However either excision or ablation, with removal of areas of scar tissue (adhesions), can be used for endometriosis that does not involve the bowel, bladder, or the tube carrying urine from the kidney to the bladder (ureter). This improves the chance of pregnancy.
Sometimes, but less often, a more traditional operation is done with a larger cut to the abdomen to remove larger patches or cysts.
If you have completed your family, and other treatments have not worked well, removal of the womb (uterus) - a hysterectomy - may be an option. The ovaries may also be removed. If your ovaries are not removed then endometriosis is more likely to return. If your ovaries are removed during a hysterectomy then you may need hormone replacement therapy (HRT) and this will need to be discussed with you.
Some general points about the treatment of endometriosis
Initial treatment without a conclusive diagnosis may be advised
The way to confirm a diagnosis of endometriosis is to have a laparoscopy (the small operation described earlier). However, many women develop symptoms that are 'probably' due to endometriosis such as painful periods - but have not yet had a laparoscopy. In such circumstances, your doctor may suggest an initial treatment of painkillers and/or 'the pill' or the levonorgestrel-releasing intrauterine system (LNG-IUS), in particular, if you require contraception as well. These treatments are used to treat period pains anyway, even without endometriosis. If the symptoms improve with this initial treatment (as often they do) then a laparoscopy may not then be needed.
Laparoscopy to diagnose and treat
A laparoscopy is done under general anaesthetic. You may have one to confirm a diagnosis of endometriosis. Your specialist may also ask for your consent at the same time to treat any large patches they may find (as described earlier) 'whilst they are in there'. This saves having two laparoscopies - one to diagnose and one to treat.
Severity and type of symptoms may influence the choice of treatment
Some women with endometriosis have no symptoms and need no treatment. If symptoms are mild, painkillers alone may be fine. Hormone treatments usually work well to ease pain but do not improve fertility. Surgery may be needed if infertility is caused by endometriosis.
Success of treatment and side-effects
Overall, the hormone treatment options all have about the same success rate at easing pain. However, some women find one treatment better than others. Also, the treatments have different possible side-effects. You may try one and it may be fine. However, it is not unusual to switch from one treatment to another if the first does not suit.
Age and plans for pregnancy
Symptoms often improve during pregnancy. Also, the longer you have endometriosis, the greater the chance of reduced fertility. You may need to take this into account if you have plans for having children. If your family is complete, your treatment options will be wider.
Length of treatment
It may take a few months of hormone treatment to get full benefit. Do persevere for a few menstrual cycles if pain does not ease straightaway. Danazol and GnRH analogues are usually only advised for six months. Symptoms may be much improved after six months of treatment, but may return once treatment is stopped. Progestogens, 'the pill' and the LNG-IUS are suitable for long-term treatment.
Once the endometriosis has gone with treatment, it may come back again in the future. Further treatment or a combination of treatments may need to be considered if symptoms do come back.
Further reading and references
Endometriosis: diagnosis and management; NICE Guidelines (Sept 2017)
Guidelines on Chronic Pelvic Pain; European Association of Urology (2015)
Endometriosis; NICE CKS, February 2020 (UK access only)
Brown J, Farquhar C; Endometriosis: an overview of Cochrane Reviews. Cochrane Database Syst Rev. 2014 Mar 103:CD009590. doi: 10.1002/14651858.CD009590.pub2.