A case of a prolactinoma resistant to dopamine agonists

Dopamine agonists are the drugs of choice in the treatment of prolactinomas, the most common type of pituitary adenomas. However, up to 25% of prolactinomas do not respond to these drugs and alternative treatments have to be considered. We describe a 37-year old female with a microprolactinoma who, although having received all available formulations of dopamine agonists over a period of 11 years, did not respond either clinically--diminution of galactorrhea and restoration of her menstrual cycle--or hormonally through normalisation of the elevated prolactin levels. Throughout the same period, the size of the adenoma remained unchanged. While on high doses of dopamine agonists, the patient presented with side effects such as nausea, vomiting, orthostatic hypotension and tachycardia without any symptoms of psychosis. Therefore, either the dose of the dopamine agonists was not toxic enough for the mesolimbic dopaminergic pathway to be activated or the patient was dopamine-resistant in this pathway as well.