From the Guidelines
No, prolactinomas do not cause decreased prolactin levels, as they are benign pituitary tumors that produce excess prolactin, leading to elevated prolactin levels in the blood (hyperprolactinemia) 1. Prolactinomas are composed of lactotroph cells that secrete prolactin autonomously, often resulting in prolactin levels that can be 10-100 times above the normal range. The elevated prolactin can cause symptoms such as:
- Irregular or absent menstrual periods
- Galactorrhea (inappropriate milk production)
- Decreased libido
- Erectile dysfunction
- Infertility Treatment typically involves dopamine agonist medications like cabergoline (0.25-1 mg twice weekly) or bromocriptine (2.5-15 mg daily), which reduce tumor size and normalize prolactin levels 1. In rare cases where medication fails or isn't tolerated, surgical removal may be necessary. If a patient with a known prolactinoma suddenly develops decreased prolactin levels without treatment, this would be unusual and might indicate pituitary apoplexy (sudden bleeding into the tumor) or other pituitary damage requiring immediate medical attention 1. It's essential to note that serum prolactin levels directly correlate with prolactinoma size and are important markers of treatment response 1. However, very high concentrations of prolactin could saturate the signalling antibody, making it less available for binding to the coupling antibody, resulting in artificially low measurements, known as the ‘high-dose hook effect’ 1. Therefore, performing serial dilutions of serum for prolactin measurement in patients with large pituitary lesions and normal or mildly elevated prolactin levels is recommended 1.
From the Research
Prolactinoma and Prolactin Levels
- Prolactinoma is a type of pituitary tumor that secretes prolactin, leading to elevated prolactin levels in the blood 2, 3, 4, 5, 6.
- The primary treatment for prolactinoma is dopamine agonists, which can reduce prolactin levels and tumor size in most patients 2, 3, 5.
- However, some patients may develop resistance to dopamine agonists, characterized by failure to achieve normoprolactinemia and significant reduction in tumor size 2.
Decreased Prolactin Levels in Prolactinoma
- There is no direct evidence to suggest that prolactinoma can cause decreased prolactin levels 2, 3, 4, 5, 6.
- In fact, prolactinoma is typically associated with elevated prolactin levels, and treatment aims to reduce these levels to normal range 2, 3, 5.
- It is possible that in some cases, prolactin levels may decrease after treatment, but this is not a characteristic of the tumor itself, rather a response to therapy 3.
Treatment Options for Prolactinoma
- Dopamine agonists, such as cabergoline and bromocriptine, are the primary treatment for prolactinoma 2, 3, 5.
- Surgery, radiotherapy, and temozolomide chemotherapy may be considered for patients who are resistant to dopamine agonists or have aggressive tumors 2, 4, 5.
- Other treatment options, such as peptide receptor radionuclide therapy and estrogen pathway modulators, are being investigated for aggressive prolactinomas 4.