a milky breast discharge occurring at anytime other than during normal breast feeding. Galactorrhea is most often seen in women with hyperprolactinemia (high blood levels of prolactin), especially in those with prolactinoma or other pituitary-related tumors. Galactorrhea often occurs in association with amenorrhea (absence of menstrual periods) because of the effect of high prolactin on LH and FSH release from the pituitary gland. Rarely men may also experience galactorrhea

Prolactinomas secrete excess prolactin and are the most common pituitary adenoma. The normal blood prolactin level is typically less than 20-25 ng/ml. In general, the prolactin level correlates with the size of the prolactinoma. 

In most women, prolactinomas are detected when they are smaller (microadenomas) and the prolactin level is moderately elevated (50 - 300 ng/ml). A relatively small elevation in prolactin will cause irregular menstrual periods or amenorrhea and galactorrhea. In contrast, in men prolactinomas are typically detected when they are larger (macroadenomas), with prolactin levels over 500 - 1000 ng/ml. Most men with a prolactinoma have some degree of pituitary failure (hypopituitarism), especially hypogonadism. Women and men also typically have a reduced sex drive (decreased libido) and weight gain. With larger tumors, headaches and visual loss (from compression of the optic nerves or optic chiasm) can occur. A minority of patients with large tumors may have hemorrhage into a tumor (pituitary apoplexy) causing rapid onset of headache, visual loss, double vision, and pituitary failure.

Prolactinomas are typically diagnosed because of problems related to high prolactin and associated hypogonadism or with macroprolactinomas, prolactinomas may cause headaches, visual loss or bleeding (apoplexy).
Hormonal diagnosis: A prolactinoma is diagnosed by demonstrating elevated blood prolactin levels. A prolactin level of over 150-200 ng/ml is almost always due to a prolactinoma. However, moderate prolactin elevations (30-200 ng/ml) can occur from other causes such as pregnancy, stress (discomfort, exercise), low thyroid function (hypothyroidism), kidney or liver failure and medications (e.g., haloperidol, antidepressants, verapamil). An additional cause of high prolactin level is "stalk compression effect" from a pituitary or brain tumor that compresses the pituitary stalk. Other adenomas, craniopharyngiomas, Rathke’s cleft cysts and other brain tumors may cause modest prolactin in the range of 40 – 150 ng/ml. 

Medical therapy: In general, the first line of treatment for patients with a prolactinoma is medication rather than transsphenoidal surgery. Approximately 80% of patients will have prolactin levels restored to normal with dopamine agonist therapy and many will have marked tumor shrinkage. The most commonly used agent is cabergoline (Dostinex) which has replaced bromocriptine (Parlodel) as the drug of choice given cabergoline’s higher success rate and lower side-effect rate. Most women have return of menses and many become fertile again. Tumor shrinkage will often results in rapidly improved vision and headache resolution. Dostinex is taken only twice per week and generally has few side effects. It is also effective in patients whose prolactinomas are resistant to bromocriptine therapy. The usual starting dose is 0.5 mg twice per week and may be increased up to 1.0 mg twice per week. Bromocriptine, if used, should be started at a low dose to minimize nausea and other gastrointestinal side effects, usually 2.5 mg tablet per day at mealtime. The dose is then increased over several days or weeks to a daily maximum usually no exceeding 10 mgs.