What is the Pituitary Gland?

The pituitary gland is a pea-sized gland located at the base of your brain behind the bridge of your nose. It is often referred to as the body’s ‘master gland’ because it controls the activity of most other hormone-secreting glands such as the thyroid, adrenals and reproductive glands. The pituitary gland produces a number of hormones including prolactin, follicle-stimulating hormone (FSH) and luteinising hormone (LH). Prolactin stimulates milk production after childbirth, but it is also produced in non-pregnant women and men, although in smaller amounts. FSH and LH act on the ovaries or testes to stimulate sex hormone production, and egg and sperm maturity.



What is a prolactinoma?

A prolactinoma is a prolactin-producing tumour of the pituitary gland and is the most common type of pituitary tumour. A prolactinoma is a benign tumour and is not a brain tumour or cancer. It grows very slowly and many do not seem to grow at all. 

The vast majority of prolactinomas are small, less than 1cm in diameter. These are called microprolactinomas. The rarer larger tumours, greater than 1cm in size, are called macroprolactinomas. Having a prolactinoma can lead to different symptoms and problems among women and men. Some of these are caused by having too much prolactin in the body, while others are linked to the size and location of the tumour. Excess prolactin, or hyperprolactinaemia, can lower levels of FSH, LH and sex hormones in both women and men. 


What causes a prolactinoma?

A prolactinoma occurs when the cells that are responsible for the production of the hormone prolactin start to multiply. We do not know what causes this to happen. They can occur in men but are more common in women under the age of 50 years old. Prolactinomas rarely run in families.


What are the symptoms of a prolactinoma?

In women, the first symptoms may relate to infrequent or loss of periods (oligomenorrhoea or amenorrhoea). Some women may also develop excess breast milk production (galactorrhoea), which may leak spontaneously. As high prolactin levels interfere with ovulation, an untreated prolactinoma can cause infertility. Women with prolactinomas do not have any increased risk of breast cancer. 

In men, excessive prolactin lowers testosterone levels and may result in a reduced interest in sex and in erectile dysfunction. Infertility due to a low sperm count may also occur.

If left untreated, prolactinomas can increase the risk of osteoporosis, or brittle bones, in both men and women as a result of persistently low levels of the sex hormones oestrogen or testosterone.

If you have a large tumour, you may have pressure symptoms such as headache or visual problems. This is because the nerves to your eyes pass over the top of the pituitary gland. Large tumours may also affect the functioning of the pituitary gland resulting in hypopituitarism (pituitary under activity) with low levels of other pituitary hormones, such as thyroid hormones and cortisol.


What else can cause a raised prolactin?

Prolactin levels normally rise during pregnancy and breastfeeding. They may also rise at other times because of:  

  1. Stress, both physical and mental, and exercise can cause a temporary rise in prolactin levels.
  2. Medication: Some medication such as those used to treat depression and other mental health disorders and medication to stop vomiting, can cause elevated prolactin levels. Make sure you tell your doctor about all your current treatments.
  3. Hypothyroidism: an underactive thyroid gland can cause elevated prolactin. 
  4. Chronic kidney disease
  5. Non-functioning pituitary tumours: These benign (non-cancerous) tumours can cause a slight rise in the prolactin levels.


How is a prolactinoma diagnosed?

The tests to diagnose a prolactinoma are relatively straightforward. They consist of blood tests to check various hormone levels and a scan of the pituitary gland to show the size of the prolactinoma.

If the blood test shows you have a raised prolactin level, this will be repeated at least once to make sure it is a true result. Another blood sample will be taken to make sure your thyroid is functioning normally and other hormones produced by the pituitary will also need to be checked.

An MRI scan (magnetic resonance imaging) is usually carried out to give detailed pictures of the pituitary gland. 

If you have any problems with your vision, you will probably be seen by an eye specialist who will check the strength of your eyesight and chart your fields of vision.


How is a prolactinoma treated?

Whatever the size of your prolactinoma, it is likely that your treatment will be with tablets. The two most commonly prescribed medications are called bromocriptine (brand name Parlodel), and cabergoline (brand name Dostinex).

These drugs act by reducing prolactin secretion by the prolactinoma. Prolactin levels often fall to normal within a few weeks of starting the treatment. In women, once prolactin has fallen to normal, menstrual cycles usually resume and fertility is restored in most cases. This may happen quite quickly, so if you do not wish to fall pregnant, then please discuss with your doctor the best method of contraception. In men, testosterone levels usually rise with normalisation of prolactin levels, which brings an improvement in your sex life.

Nearly all prolactinomas shrink in size following treatment with the above tablets. If your prolactinoma is pressing on the nerves to the eyes, there is a good chance that your vision will improve as the tumour shrinks. If you have a larger prolactinoma, you may have several pituitary scans over the months and years so that shrinkage can be measured. 

Very few patients with microprolactinomas will require surgery or radiotherapy. For the minority of patients with macroprolactinomas which do not shrink following medical treatment, surgery may be required, particularly if your vision has not improved.

If you have pituitary underactivity then hormone supplements may also be required. These may include steroid tablets for adrenal underactivity, thyroid hormone tablets for thyroid underactivity and possibly oestrogen for women or testosterone supplements for men.

The outcome for patients with prolactinomas is usually excellent as the majority respond well to medication. However, you may have to take these medicines for a few years to prevent the tumour from growing back. After 2-3 years, the medicines may be slowly reduced and stopped if prolactin levels are normal and the tumour is no longer visible.


Where can I learn more? 

Contact the Pituitary Foundation at:

Pituitary Foundation

PO Box 1944

Bristol BS99 2UB

Tel: 0845 450 0375

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