Prolactinoma and
Hyperprolactinaemia
Hyperprolactinaemia
Hyperprolactinaemia is commo actice, occurring more
commonly in women than men. Demonstration of persistent hyperprolactinaemia is
important because repeat prolactin measurement may be normal. Pregnancy is a
common cause of hyperprolactinaemia, and should be considered before further investigation.
A full drug history is required because dopamine antagonists such as
anti-emetics and antipsychotics commonly cause an elevation in prolactin.
Classic features of hyperprolactinaemia include menstrual disturbance, reduced
fertility and galactorrhoea. Profound hypothyroidism can cause
hyperprolactinaemia by TRH-driven prolactin secretion. Polycystic ovary
syndrome is commonly associated with mild hyperprolactinaemia, with prolactin
levels typically <1000 miU/L together with symptoms of androgen excess. In
large pituitary tumours, a prolactin level >5000 iU/L suggests a
macro-prolactinoma rather than a non-functioning adenoma.
Prolactinoma
Clinical presentation
Micro-prolactinoma
These are the most common pituitary tumours and are more
frequently seen in women than men. Micro-prolactinomas are <1 cm, and
typically present with menstrual disturbance and galactorrhoea, although
infertility may be the only feature (Figure 6.1). Migrainous headaches can be a
feature, probably because of endocrine disturbance in individuals predisposed
to migraine, rather than mass effect. Polycystic ovary syndrome is
distinguished from prolactinomas by the presence of androgenic symptoms, less
elevated prolactin levels (typically <1000 miU/L) and the absence of a pituitary
lesion on MRI. Occasionally, micro-prolactinomas can be so small that they are
not seen on MRI.
Macro-prolactinomas
By definition these are >1 cm and can be very large.
They are more common in men than women, and patients typically present with mass
symptoms of visual field loss and headache, particularly if there is cavernous
sinus invasion. Prolactin levels are typically >5000 miU/L and can be in the
hundreds of thousands, which is virtually diagnostic of a macro-prolactinoma
(Figure 6.1). When levels of prolactin are extremely high, the immunoassay can
give inaccurately low results for methodological reasons (called the hook
effect) so it may be necessary to dilute the sample to achieve a more accurate
result.
Treatment
Prolactinomas are treated with dopamine (D2) agonists, most
commonly cabergoline and bromocriptine (Figure 6.1). Cabergoline is given once
or twice weekly and is better tolerated than bromocriptine, which is given
daily. Common side effects include nausea and postural hypotension, and rarely
psychiatric disturbance. Bromocriptine is preferable to cabergoline in women
who are trying to conceive.
Macro-prolactinomas are treated medically even if they are
very large, usually with good reduction in prolactin and tumour bulk (Figure
6.2). In 10% of macro-prolactinomas, cerebrospinal fuid (CSF) leak occurs as a
result of the rapid reduction in the size of the lesion. This is important to
recognise as it is a potential source of meningitis.
Surveillance and long-term follow-up
The aim of treatment is resolution of symptoms and
normalisation of prolactin using the lowest possible dose of dopamine agonist
medication. Micro-prolactinomas are usually treated with dopamine agonists for
2–3 years and then discontinued to see if there is remission. A convenient time
for discontinuing treatment is after menopause, because prolactinomas are
oestrogen-driven. Macro-prolactinomas require higher doses of dopamine agonists
and commonly recur so treatment time is longer. A high cumulative dose of
dopamine agonist can lead to cardiac valve abnormalities, although this is not
a concern in the usual dosage needed to treat micro-prolactinomas.
Pituitary incidentaloma
Approximately 1 in 10 people have an incidental pituitary
lesion, which may be of no clinical significance. Increased access to MRI scans
has led to an increase in their detection. The majority of incidentalomas are
micro-adenomas. Serum prolactin should be checked and if there are signs of
acromegaly, Cushing’s or hypopituitarism, appropriate basal and dynamic tests
should be performed. If there is thickening of the pituitary stalk on MRI,
serum and urine osmolalities should be checked to exclude diabetes insipidus,
especially if there is polyuria and polydipisia. Local protocols will guide
further imaging, but patients can often be reassured and event if there is no
growth detected on serial scans.
