Approach
Hyperprolactinaemia in premenopausal women results in galactorrhoea, menstrual irregularity, and infertility. Galactorrhoea is less common in post-menopausal women due to oestrogen deficiency. Men may also present with symptoms of secondary hypogonadism, such as reduced libido, impotence, and infertility. Later presentation in men and post-menopausal women means that these patients are more likely to present with locally invasive tumours which may compress adjacent structures in the suprasellar region (optic tracts or chiasm) or the parasellar cavernous sinuses (other cranial nerves), causing mass effect features (e.g., visual disturbances, ophthalmoplegia, headaches). Chronic hyperprolactinaemia with subsequent secondary hypogonadism may lead to osteoporosis.
Hormonal determination
A single measurement of serum prolactin taken without significant venepuncture stress is sufficient to establish the diagnosis of hyperprolactinaemia. In cases of mild hyperprolactinaemia, it may be worth measuring several sequential prolactin measurements, separated by at least 20 minutes and taken via an indwelling cannula in order to minimise venepuncture stress. Secondary causes should be excluded by a careful history, examination, and pregnancy test. Mild prolactin level elevations, <2000 mIU/L (<100 micrograms/L), can occur with certain drugs, including typical and atypical antipsychotics (e.g., phenothiazines, risperidone, clozapine), opiates, anti-emetics (e.g., metoclopramide, domperidone), oestrogens, H2 blockers, and verapamil. Therefore it is important to take a full drug history.
Prolactin levels can be elevated in renal failure and in primary hypothyroidism, so renal and thyroid function should be checked prior to further investigating a raised prolactin level. Generally, prolactin levels associated with prolactinomas correspond with tumour size.[11] Most patients with a microprolactinoma will have a serum prolactin level between 2000 and 4000 mIU/L (100 and 200 micrograms/L), and a level of >5000 mIU/L (>250 micrograms/L) is almost certainly a macroprolactinoma.[12] In non-functioning pituitary adenomas, disconnection hyperprolactinaemia can occur. This is where prolactin is raised due to pituitary stalk compression impeding dopamine transport via the portal vessels to the anterior pituitary. In this setting, serum prolactin is normally <2000 mIU/L (<100 micrograms/L).[12]
In cases of significant hyperprolactinaemia, gonadotrophins (follicle-stimulating hormone, luteinising hormone) and estradiol/testosterone may be low, consistent with secondary hypogonadism. All patients, but particularly those with macroprolactinomas, should have assessment of the remainder of their pituitary function. Up to 50% of patients with growth hormone (GH)-secreting tumours causing acromegaly also have hyperprolactinaemia.[11] Therefore it is important to exclude this condition in patients with an elevated prolactin using clinical assessment, and random GH and insulin-like growth factor 1 measurement.
Pituitary imaging
A gadolinium-enhanced magnetic resonance imaging is required to confirm the diagnosis of a prolactinoma. Computed tomography does not provide sufficient pituitary visualisation.
Visual-field examination
Clinical visual-field examination is performed in all patients as part of the initial patient assessment. However, computerised visual field examination (perimetry) is also required in all patients with a macroadenoma with suprasellar extension to exclude the existence of optic chiasmal compression.
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