A prolactinoma is a non-cancerous swelling in the pituitary gland, which makes too much of a hormone called prolactin. This can cause various symptoms including reduced fertility, breast changes, and headaches. In children there may be reduced growth or delayed puberty. Prolactinomas can be treated successfully, usually with medication. The medication may be needed long-term. You will need to have follow-up checks because prolactinomas can come back.
What are prolactinomas?
A prolactinoma is a benign tumour (non-cancerous swelling) in the pituitary gland. Prolactinomas make large amounts of a hormone called prolactin.
The pituitary gland lies just below the brain. It makes several hormones, including a hormone called prolactin. (A hormone is a chemical which is made in one part of the body, but passes into the bloodstream and has effects on other parts of the body.)
Prolactin helps the body to produce milk when a woman breast-feeds. It also has effects on other hormones in the body.
What causes prolactinomas?
A prolactinoma occurs when some of the cells in the pituitary gland (the ones producing prolactin) multiply more than usual. We do not know what makes the cells multiply in the first place. In rare cases, there may be an inherited (genetic) cause.
What are the different types of prolactinoma?
Small prolactinomas (less than 10 mm) are called microprolactinomas. Larger ones (more than 10 mm) are called macroprolactinomas. There is also a rare type called giant prolactinomas, which are more than 4 cm.
Who gets prolactinomas?
About 1 in 10,000 people develop a prolactinoma. Prolactinomas are most common in women aged 20-50 years, but they can occur at any age and in men too. Prolactinomas are the most common type of pituitary gland tumour.
What are the symptoms?
High levels of prolactin in the blood can cause various symptoms. The symptoms differ slightly between men, women and children.
Women may have:
- Irregular periods or no periods.
- Reduced fertility.
- Reduced sex drive.
- Milk leaking from the breasts (known as galactorrhoea). The milk may leak out by itself, or may only show when the breast is squeezed. (Note: leakage of milk from the breasts is normal towards the end of pregnancy, with recent childbirth, if breast-feeding, and for some time after finishing breast-feeding.)
- Increased growth of hair on the face or body.
Men may have:
- Reduced fertility.
- Erectile dysfunction (difficulty having an erection).
- Reduced sex drive (libido).
- Breast enlargement (called gynaecomastia).
- Very rarely, leakage of milk from the breasts.
Children and teenagers may have:
- Reduced growth.
- Delayed puberty.
Prolactinomas which are large may press on the brain or nearby nerves (the nearest nerves are the optic nerves which go to the eye). This may cause symptoms such as:
- Eye symptoms - you may get reduced vision or double vision. The early changes can easily go unnoticed, because they affect the peripheral vision - that is, the edges of your vision to the extreme left and right. This means that you may see less of what is around you, but can still see well if you focus on something directly.
If you have headaches or reduced vision, see a doctor urgently - you may need to have treatment promptly to relieve the pressure on the optic nerves.
Rarely, the prolactinoma may press on the rest of the pituitary gland, stopping it from producing other hormones. This can cause symptoms such as tiredness, fainting, low blood pressure, low blood sugar or collapse. Also (rarely) there may be a leakage of the fluid that surrounds the brain and pituitary gland, felt as watery fluid leaking through the nose. These symptoms need urgent treatment.
How is prolactinoma diagnosed?
The diagnosis may be suspected from the symptoms. Women tend to be diagnosed earlier than men, because a change in the woman's periods is an early symptom and is easily noticed. Some prolactinomas are diagnosed by chance, if you have tests for another reason. If a prolactinoma is suspected, you may be offered several tests.
A blood sample to check the level of prolactin in the blood. If a high prolactin level is found, you may be asked to have a repeat test. This is because prolactin levels can be affected by many other things in the body, such as sleep or stress. It may help to take the blood sample when you are reasonably rested and have been awake for at least two hours.
The normal level of prolactin is less than 400 mU/L. A very high prolactin level (>5000 mU/L) usually means that a prolactinoma is present. Levels in between may be due to a prolactinoma, or to other causes (see 'What else could it be?', below).
Other blood tests may be done at the same time. It is important to test the thyroid gland and to check kidney function, as both these can affect prolactin levels. Further tests may be needed to see if the tumour is causing a lack of other hormones made by the pituitary.
Eye tests will assess if the tumour is pressing on the optic nerve - this includes a test of visual fields.
A magnetic resonance imaging (MRI) scan or a computed tomography (CT) scan can show the size of the tumour. A bone density scan may be advised for some patients, to check whether they are at risk of 'thinning' of the bones (osteoporosis), which is a possible complication - see below.
What else could it be?
Apart from prolactinomas, there are other causes of raised prolactin levels. For example, some medicines may cause high prolactin levels. These include:
- The anti-sickness medicines metoclopramide and domperidone.
- Antidepressants of the selective serotonin reuptake inhibitor (SSRI) type.
- Some medicines used to treat schizophrenia or bipolar disorder.
There are other less common causes for a raised prolactin level.
What are the treatment options?
Treatment usually works well to stop the symptoms of prolactinoma and to improve fertility. There are various treatments - the usual one is medication.
Note: if you are a woman starting treatment for a prolactinoma, remember that the treatment could improve your fertility quite quickly, and you could possibly become pregnant before you even have a period. So, if you do not want a pregnancy, you will need to use contraception. Discuss this with your doctor, nurse or family planning clinic if you need advice.
Not treating may be an option
For a small prolactinoma (a microprolactinoma), if symptoms are not too troublesome then one option is just to monitor the situation. This means having repeat blood tests and possibly scans at regular intervals. If symptoms get worse or the prolactinoma seems to be growing, treatment can be started whenever necessary.
If you are choosing the no-treatment option, your doctor may advise taking maintenance hormone treatment - to provide oestrogen hormones (for women) or testosterone hormones (for men). This is because prolactinomas can cause low oestrogen or low testosterone levels in the body. In the short term, low oestrogen and low testosterone levels are not harmful. However, in the long term, this could lead to 'thinning of the bones' (osteoporosis). Also, you may feel better if you have enough oestrogen or testosterone in your body.
For women, oestrogen may be taken in the form of the combined oral contraceptive pill or as hormone replacement therapy, depending on her age and whether she needs contraception. For men, testosterone can be taken by mouth, in patch or gel form or by injection once a month.
Medication is a very effective treatment for most prolactinomas. The medication is a type called dopamine agonists. These act on the pituitary gland to reduce the amount of prolactin it makes, and they can also shrink the tumour. Usually with this medication, prolactin levels go down to normal in a few weeks. Dopamine agonists can be taken as long-term treatment.
Are there any side-effects of dopamine agonists?
Possible side-effects are:
- A feeling of sickness (nausea)
- Low mood
A rare side effect is psychosis (disturbed thinking) - which clears up if the medication is stopped. Side-effects are less likely if you start with a low dose and increase gradually.
Note: if you feel drowsy, do not drive or use dangerous machinery.
Some people may get low blood pressure during the first few days of starting treatment. This can cause faintness or dizziness. If this happens, your blood pressure may need monitoring, and do not drive or use machinery until you feel well.
There have been concerns that dopamine agonists may cause hardening and damage (fibrosis) of internal organs - if taken in high doses long-term. It is still uncertain how much of a risk there is from these medicines. Many specialists think that the risk of fibrosis is low, and that for most patients, the benefits of treatment outweigh the risks.
The current advice for people taking long-term treatment with dopamine agonists is that you should be monitored for fibrosis, although in most cases this is simply a precaution:
- Before starting treatment, have an ultrasound test of the heart (an echocardiogram) to check the heart valves. Your doctor should consider arranging a blood test and chest X-ray too, to check for signs of fibrosis or inflammation.
- You should be monitored for symptoms such as shortness of breath, cough, heart problems or tummy (abdominal) pain.
- Regular tests on the lungs (lung function tests) may be advised.
- If you take cabergoline or pergolide you should have an echocardiogram within 3-6 months of starting treatment and then at 6-12-month intervals.
What about treatment in pregnancy? If you are planning a pregnancy, it is best to discuss treatment options with your doctor beforehand. Treating the prolactinoma usually improves fertility, so can help you become pregnant. Bromocriptine is thought to be the safest of the dopamine agonists for pregnancy, because it is the most tried and tested one. Many women have had babies after taking bromocriptine.
Discuss with your doctor what to do if you become pregnant. Some women are advised to stop medication during all or part of the pregnancy. Bromocriptine can be used in pregnancy if required.
During pregnancy, some prolactinomas can get bigger. If you have any symptoms such as headache or reduced vision, see a doctor immediately so that this can be checked.
Surgery may be an option if medication does not work, is not wanted, or for larger prolactinomas. The operation is called trans-sphenoidal surgery, because the surgeon gets to the pituitary through the sphenoid bone, via a small cut above the upper front teeth or from inside a nostril. It is done under general anaesthetic.
Radiotherapy (X-ray treatment) focuses high-intensity radiation at the prolactinoma, to destroy the abnormal cells. It is not usually needed for prolactinomas - however, it may be used rarely, if other treatments are not sufficient. It can have side-effects.
Sometimes prolactinomas cause a reduction in the other hormones that the pituitary gland produces. If so, you may need to take tablets to replace these hormones. This will depend on your symptoms and blood test results.
What are the possible complications?
The main complication is the risk of 'thinning' of the bones (osteoporosis), if high prolactin levels are untreated for a long time (over one year). This is because the high prolactin reduces oestrogen or testosterone levels, which can lead to osteoporosis. Osteoporosis can be prevented by treating the prolactinoma (as above), which reduces prolactin levels. Alternatively, replacement oestrogen or testosterone can be taken.
Large prolactinomas may cause complications if they grow and press on the structures nearby: the pituitary gland, the brain and the nerves to the eye. To prevent this, large prolactinomas should usually be treated. If untreated, the pressure might eventually lead to loss of vision, other hormone problems (which could cause severe illness) or severe headaches.
Rare complications are:
- A leak of fluid from around the brain into the nose, which means that there is a risk of infection such as meningitis.
- Pituitary apoplexy, which is a rare but serious complication, when there is a bleed inside the tumour, making it suddenly expand. This causes sudden increasing symptoms such as headache and reduced vision, and may cause collapse. It needs urgent treatment and may require surgery.
- The possibility, which is extremely rare, of a prolactinoma being cancerous (malignant).
What is the outlook (prognosis)?
The outlook is very good. Most prolactinomas are successfully treated with medication. If this does not work, surgery is usually successful. Treatment for women can restore periods and fertility (assuming that the fertility problem was due to the prolactinoma). For men also, fertility can improve with treatment, but you may need to take additional medication called gonadotrophins in order to father children.
For some people, the prolactinoma itself may be cured after about three years of taking medication. So you may be able to come off treatment.
Prolactinomas can come back (recur), even after successful treatment with medication or surgery. You will still need monitoring (such as regular blood tests) to check that the prolactinoma has not come back. If it has, then treatment can be restarted.
Dr Tim Kenny
Dr Colin Tidy
Dr John Cox