Pituitary adenomas are one of the most common causes of infertility in women. Because of the pituitary gland’s role in the regulation of prolactin secretion, a secretory adenoma (prolactinoma) adversely affects endometrial binding proteins and can result in chronic infertility or low fertility. These tumors can be clinically silent until becoming a space-occupying problem with impingement on the optic chiasm resulting in clinical blindness. Thus, the majority may go undiagnosed due to insignificant clinical symptoms. Treatment of pituitary microadenomas in women is performed medically with bromocriptine or cabergoline.
A 17-year-old primiparous western lowland gorilla was diagnosed with hyperprolactinemia following multiple failed embryo transfers. Serum prolactin was 302 ng/ml (normal range 1.9–25 ng/ml). An MRI was performed and revealed a pituitary microadenoma involving the pituitary stalk as well as the pituitary body. Treatment was initiated with cabergoline (Dostinex, Pfizer Inc., New York, USA) PO twice weekly. A recheck of the serum prolactin at 3 months still showed elevated levels, so the dose was increased. After 6 months of therapy, a repeat MRI was performed and the tumor was notably smaller. Serum prolactin at this time was within normal limits and treatment was discontinued. Subsequently, the animal was seen breeding regularly and had a positive pregnancy test 6 months later.
Hyperprolactinemia in women can be caused by physiologic disorders, medications, pituitary disorders, or hypothyroidism. In this case, hypothyroidism was ruled out based on normal TSH (3.16 ng/ml, ref. 0.4–4.0 ng/ml) in conjunction with elevated serum prolactin. Medical treatment for microadenomas is generally successful after 6–12 months. In this case the animal was treated for 8 months and a repeat MRI and serum prolactin indicated that the tumor had resolved. The subsequent pregnancy confirmed successful treatment.