Q: What are the possible etiologies for elevated prolactin?
The causes of hyperprolactinemia fall into three categories: physiologic, pharmacologic, and pathologic.2 The table provides examples from each category.
A nonsecretory pituitary adenoma or any lesion in the brain that would disrupt the hypophyseal stalk may interfere with dopamine’s inhibitory control and thereby increase prolactin. This is called the stalk effect. It is important to note that not all MRI-proven pituitary adenomas are prolactin secreting, even in the presence of hyperprolactinemia. According to an autopsy series, about 12% of the general population had pituitary microadenoma.3
There is rough correlation between prolactinoma size and level of prolactin. Large nonsecretory pituitary adenomas have prolactin levels less than 150 ng/mL. Microprolactinomas (< 1 cm) are usually in the range of 100 to 250 ng/mL, while macroprolactinomas (> 1 cm) are generally
≥ 250 ng/mL. If the tumor is very large and invades the cavernous sinus, prolactin can measure in the 1,000s.3
Polycystic ovarian syndrome (PCOS) is a common disorder affecting women of reproductive age and the most common cause of underlying ovulatory problems. Patients with PCOS can have mildly elevated prolactin; the exact mechanism of hyperprolactinemia in PCOS is unknown. One theory is that constant high levels of estrogen experienced in PCOS would stimulate prolactin production. It is important to rule out other causes of hyperprolactinemia before making the diagnosis of PCOS.
What is the clinical significance of elevated prolactin? Why do we have to work up and treat it? See answer on the next page...