A prolactinoma is a prolactin-secreting tumour of the anterior pituitary, and its effects come from two distinct sources: the excess prolactin acting on the gonadal axis, and the mass of the tumour pressing on nearby structures. That division between hormone-induced and tumour-induced effects shapes how a prolactinoma presents in women, in men, and before puberty.
What a prolactinoma is
Prolactinoma, or a tumour arising from the lactotrope cells of the anterior pituitary gland, is the most common pituitary adenoma, accounting for more than 50% of all pituitary adenomas and about half of all functioning pituitary tumours. Mixed tumours such as GH (growth hormone) and PRL (prolactin), ACTH (adrenocorticotropic hormone) and PRL, and TSH (thyroid-stimulating hormone) and PRL can also be seen.
Micro- and macroprolactinoma
Prolactinomas are grouped by size. The threshold for microprolactinoma and macroprolactinoma is 1 cm of diameter. Among people with a prolactinoma, microprolactinoma is 20 times more prevalent in women, while the prevalence of macroprolactinoma is equal in men and women.
Prolactin behaves in the completely opposite way to GH: in GH-secreting tumours the GH level does not correlate with the size of the tumour, whereas in prolactinoma the level of prolactin secretion is always correlated with the size of the tumour.
Age and sex at diagnosis
The mean age of diagnosis in women is about 30 years, while in men it is mostly diagnosed after the age of 50. Microadenoma is more common in women, while men more often present with a macroadenoma. The size at diagnosis matters for presentation, as the sections on women and men show.
Hormone-induced and tumour-induced manifestations
The clinical manifestations of hyperprolactinemia can be divided into:
- hormone-induced clinical manifestations — galactorrhea and amenorrhea
- tumour-induced clinical manifestations — headache, visual disturbances and hypopituitarism (deficiency of the other pituitary hormones)
Manifestations in women
The main manifestations related to hyperprolactinemia in women are amenorrhea, galactorrhea and infertility.
Amenorrhea — oligo- or amenorrhea is present in more than 85% of the women with prolactinoma — happens because prolactin is able to block the activity of the pulse maker of the GnRH (gonadotropin-releasing hormone) releasing cells in the hypothalamus, disrupting the physiological pulsatility of the GnRH release. If amenorrhea happens before the menarche in women it leads to primary amenorrhea; mostly, though, hyperprolactinemia occurs after menarche and firstly leads to oligomenorrhea and finally to amenorrhea. If the amenorrhea persists, bone density is reduced in comparison with others of the same age, because of the low level of estrogen in these patients. Galactorrhea is present in about 85% of the cases, and infertility is common.
The association is not symmetrical. In more than 85% of the women with prolactinoma there is amenorrhea; conversely, only in 15% of the women with amenorrhea is there hyperprolactinemia, and in more than half of them the cause is prolactinoma.
Manifestations in men
Mostly men show the clinical manifestations in the later stages, when the size of the adenoma is quite big. In more than 80% of men the tumour is a macroadenoma, with more aggressive behaviour than in women, so tumour-related manifestations dominate: visual loss, thyroid dysfunction and adrenal dysfunction. Decreased libido and infertility are also common, and in the long term without control the persistent hypogonadism can cause osteopenia, reduced muscle mass and decreased beard growth.
Before puberty
Occurrence of hyperprolactinemia during childhood before puberty can lead to pubertal arrest, because hyperprolactinemia blocks the GnRH pulsatility which has an important role in the initiation of physiological puberty.