Giant Prolactinoma Resistant to High-Dose Cabergoline in a Young Male Lost to Follow-Up

Pituitary adenomas are neoplasms of the adenohypophysis (anterior pituitary gland) that can cause a multitude of symptoms secondary to the hormones they secrete (functioning adenomas) or mass effect on the optic chiasma (non-functioning adenomas). Functioning adenomas can secrete prolactin, growth hormone, adrenocorticotrophic hormone (ACTH) or thyroid-stimulating hormone, with some adenomas co-secreting more than one. This can lead to symptoms of prolactinoma, acromegaly, Cushing's disease, and TSHoma dependent on the elevated hormone. In non-functioning adenomas, visual changes, and headaches are seen. This case report follows a 19-year-old male who presented with visual acuity loss and persistent headaches, later diagnosed as a pituitary macroadenoma with a prolactin level of 794,560 mIU/L. He was subsequently treated with off-label cabergoline over three times the therapeutic limit for approximately 10 years. He was unfortunately lost to follow-up and unmonitored during this time, where he developed an impulse control disorder and showed inadequate response to the high-dose cabergoline. At the time of re-presenting to outpatient clinics, his adenoma was found to be extending into the cavernous sinuses with tentorial involvement, reducing the potential for surgical management. Discussions around medical, surgical, and radiotherapeutic management are being raised in light of this cabergoline resistance and placement. The case overall highlights the complexities of managing giant, dopamine agonist-resistant prolactinomas, especially in the setting of delayed follow-up, incomplete biochemical control, and neuropsychiatric side effects.