Introduction

Prolactinoma is a common benign tumour of the pituitary gland, occurring in about 1 in 10,000. It is the most frequent type of hormone-producing pituitary tumour. Prolactinomas cause symptoms due to excess secretion of the hormone prolactin, which is secreted by the pituitary gland.

Prolactin is best known for its role in stimulating milk production after childbirth, hence the name of the hormone. It also affects reproductive function and behaviour. Prolactin hypersecretion, whether from a prolactinoma, another r type of pituitary tumour, or from a disorder of the hypothalamus, suppresses the secretion of GnRH (gonadotropin releasing hormone) which can cause a lack of menstruation, infertility, decreased libido, impotence and abnormal milk production in those assigned males at birth (AMAB).

This can cause knock-on effects on other hormones. In those assigned females at birth (AFAB) who are neither pregnant nor lactating, hypersecretion of prolactin can cause the absence of menstruation, infertility, and in some cases, galactorrhea (abnormal milk production) and/or menopausal symptoms. Unfortunately, some of these effects in reproductive aged people AFAB can be mistaken for stress and low nutrition. 

Definition of prolactinoma

Prolactinoma is a health condition that emerges when a non-cancerous tumour forms in the pituitary gland—a pea-sized organ located at the base of your brain. This gland is like the control centre for most of the hormones in your body, including prolactin. Prolactin's main job is to promote milk production in people AFAB after childbirth, but it has other roles too, such as affecting reproductive functions and behaviours.

When someone has a prolactinoma, this tiny tumour starts producing prolactin in excess. It is similar to a tap that has been left on, causing the levels of prolactin in the blood to rise higher than normal. This can lead to a variety of symptoms, depending on your sex, such as changes in menstrual cycles for people AFAB, decreased sex drive in both those AMAB and AFAB, and even fertility issues.

Prevalence of prolactinoma

Prolactinomas rarely occur in paediatric cases. It only accounts for less than 3% of intracranial tumours of childhood. In adults, prolactinomas are the most common pituitary tumour, representing approximately 40% of all pituitary tumours.³ While there is no racial predisposition to prolactinoma, the prevalence is far greater in people AFAB than people AMAB.²

It can take years to diagnose this silent disease due to its nonspecific symptoms.¹ The incidence of prolactinoma varies greatly, probably according to environmental factors, as well as genetic ones, which themselves are poorly understood at present. The prevalence of diagnosed prolactinoma is about 100 per million, although the prevalence in autopsy studies suggests that many of these tumours never come to clinical attention, and are probably not pathological.

The AFAB to AMAB ratio is about 10:1 for recognised diseases, with a lower ratio in older age groups. This may not be a true representation, as the different manifestations and effects of the disease in those AMAB may delay diagnosis because the possibility of prolactinoma is not considered.⁴

Common symptoms of prolactinoma

Decreased libido (sex drive) and mood changes

Both AMAB and AFAB can experience a decrease in sexual desire as a result of elevated prolactin and prolactinoma. A thorough medical history, physical exam, and blood testing for hormone levels are also important in evaluating this problem (dopamine has not been linked in any way to prolactin or prolactinoma).⁵

Prolactin itself does not cause a loss of energy, mood changes, depressive thoughts, or a decreased interest in life. But, as discussed, increased prolactin can interfere with other hormone levels. High prolactin and low dopamine can promote changes in mood and energy. High levels of prolactin and low levels of estrogen and testosterone can cause problems with mood, energy levels, and cognitive and visual-spatial skills.⁶ 

Infertility or difficulty getting pregnant

Because infertility can be multi-factorial, patients with fertility problems should have a complete history and physical examination to help identify other factors that may contribute to the problem. High levels of prolactin can stop the secretion of the hormones that are needed to ovulate. Without ovulation, a person AFAB cannot conceive.

This is why the symptoms of high prolactin levels are often found in infertile AFAB. Prolactin-induced infertility is usually more common in those AFAB with irregular menstrual periods, galactorrhea, and who had normal menstrual cycles before the onset of taking birth control pills.

Galactorrhea (abnormal breast milk production)

Both those AMAB and AFAB may have the problem of "abnormal" (not associated with pregnancy or breast-feeding) milk secretion (galactorrhea). A comprehensive medical history, physical examination, and a series of blood tests can help determine if a patient has a prolactinoma. In addition to measuring the levels of various hormones, the doctor will need to rule out other causes of abnormal milk secretion such as a thyroid or other hormonal problem. Expansion to the word "Galactorrhea," we find that it derives its name from the Greek language.

Gála means milk and rhoía means flow. This can happen in both people AMAB and AFAB, but when it occurs in those AFAB who are not pregnant or breastfeeding, this is an unusual occurrence. It can be described as the spontaneous flow of milk from the breast and can occur at any age. The severity can also vary, with some people AFAB finding just a few drops of milk on a rare occasion after stimulation of the nipple, to others finding that it has occurred in large amounts and they may actually have seen milk on their clothes without any stimulation at all.

This can be very troubling for them at what can already be a difficult time of discovery for their symptoms. It is recommended that a bra that is designed to be more compressive should be worn to try and lessen the stimulation to the nipples. This may help, but some may still require a bra with cotton wool inserts to absorb any milk discharge.

This symptom is obviously detrimental to a person AFAB trying to live a normal life and can cause a huge deal of embarrassment and distress. It is important that the root cause is discovered and the correct treatment is then taken, as long-term milk production can lead to osteoporosis due to the lack of calcium.⁷

Irregular menstrual periods

Those who are not pregnant or nursing and have stopped menstruating should consult their physicians. Irregular menstrual periods are quite common in those with prolactinoma. The high level of prolactin in the blood causes a decrease in normal levels of estrogen, which is what causes irregular periods.

Estrogen is what builds up the lining of the uterus. When there are low levels of it, the lining does not build up normally. Then, when it comes time for the menstrual period, there is less to shed, causing the period to be lighter or the woman may skip periods. This is why hormone imbalances are a common cause of missed periods.

This also causes infrequent periods. Less common causes of irregular periods include too much prolactin, a thyroid disorder, an eating disorder, or heavy stress or anxiety. All of these can alter the body's normal hormone levels, leading to irregular 

Erectile dysfunction in males

AMAB sexual function is governed by two major neurogenic erection management systems located in the brain. The hypothalamic pituitary axis is of critical importance in the control of libido, and the initiation and maintenance of sexual function. Prolactin has a negative modulating relationship with the hypothalamic pituitary axis and high levels of prolactin can lead to a reduction in testosterone secretion which would lead to a hypogonadal state in the man causing a loss of libido and possibly erectile dysfunction.

Erection in those AMAB is largely a hydraulic event that is achieved by relaxation of the arteries in the penis that allow blood to fill the erectile tissue and achieve erection. This is then maintained by an increased intracavernous blood pressure due to decreased blood outflow occurring through a combination of neurologically mediated events and the endocrine modulation of smooth muscle tone. It is this pressure that gives rigidity to the penis.

Testosterone is known to be the major endocrine regulator of penile erection and rigidity and is produced by the Leydig cells of the testis. High levels of prolactin have been associated with erectile dysfunction and a decrease in rigidity of the penis. This is because prolactin has a suppressive effect on the gonadotrophin releasing hormone which will lead to a reduction in testosterone secretion. High levels of prolactin have also been associated with a decrease in libido through unknown means, one study found that those with raised prolactin levels had orgasms half as often as those with normal levels of prolactin.⁸ 

Other general symptoms

Headaches 

Imagine your brain is like a room, and prolactinoma is an uninvited guest taking up space. As it grows, it starts to push against the walls (in this case, your skull), and this pressure can lead to some pretty nasty headaches. 

Visual impairments 

This same uninvited guest, prolactinoma, can also lean on the nerves that connect your eyes to your brain. These nerves are important because they help you see. If the tumour presses on them, it's like someone is partially blocking the screen at a movie theatre, making it hard to see the whole picture. This can cause vision problems or even loss of peripheral vision, making it difficult to see things to your side without turning your head.

Bone density loss 

Lastly, prolactinoma can lead to lower levels of sex hormones like estrogen and testosterone, which are crucial for keeping your bones strong. This means that prolactinoma could make your bones more fragile, increasing the risk of fractures or osteoporosis over time.⁹ 

Diagnostic approaches

Blood tests to measure hormone levels

A blood test can show doctors the levels of prolactin in your body. If prolactin levels are higher than usual, it might indicate that prolactinoma is the reason. It’s a quick way for doctors to see if something's wrong with your hormone levels.

Magnetic resonance imaging (MRI) 

An MRI takes pictures of the inside of your body It uses a large magnet and radio waves to create pictures of your brain. If there’s a prolactinoma, the MRI can spot it, showing exactly where it is and how big it is. This helps doctors get a clear view of what they’re dealing with.

Visual field tests 

Since prolactinoma can press on the nerves that affect your vision, doctors might check your eyesight with visual field tests. It helps doctors understand if the tumour is affecting your ability to see around the edges of your vision.

Physical examination 

They might check for signs of prolactinoma like unexpected milk production, visual problems, or changes in your menstrual cycle or sexual function.

Summary

Quick recap: We've dived into what prolactinoma is— a usually benign tumour in your brain's pituitary gland. This little troublemaker can throw your body's prolactin levels out of whack, leading to all sorts of symptoms like changes in your vision, mood swings, headaches, and even affecting bone strength. It can mess with those AMAB and AFAB reproductive functions too, leading to issues like decreased sex drive and fertility problems.

Why catching it early matters: Finding and treating prolactinoma sooner rather than later can make a big difference. Early diagnosis means you can tackle the symptoms before they get too serious, helping prevent complications down the line. Think of it as catching a small leak before it floods your entire house—it saves a lot of hassle and keeps you healthier in the long run.

A nudge to get checked: If you're noticing any of the symptoms we talked about, don't just brush them off. It's easy to think it might be stress or just a phase, but it's worth talking to a doctor about it. If something feels off, getting it checked out is the smart move.