MON-115 - Cabergoline as First-Line Therapy in A Giant Adolescent Macroprolactinoma.

A 16-year-old male presented with a two-year history of progressive visual symptoms, peripheral field loss, and worsening headaches. Ophthalmologic evaluation detected a visual field defect (bitemporal hemianopia), consistent with interrupted optic chiasma. He denied polyuria, polydipsia, adrenal insufficiency symptoms, or hypoglycemia but reported fatigue, absence of spontaneous erections, and limited linear growth. MRI revealed a large pituitary macroadenoma measuring 3.2 × 3.0 × 2.6 cm. Hormonal testing showed markedly elevated prolactin levels >4700 ng/mL (normal 2.8–11), consistent with a macroprolactinoma. Surgical management was the first-line therapy due to visual involvement. Still, the endocrine and neurosurgery teams agreed to initiate cabergoline at 0.25 mg, titrated to 2.5 mg weekly, resulting in symptomatic improvement and a reduction in prolactin to 16.9 ng/ml. Follow-up evaluation demonstrated secondary hypogonadism, leading to initiation of testosterone replacement. GH stimulation testing showed a peak GH of 1.1 ng/mL, confirming severe growth hormone deficiency. Other labs showed normal sodium, normal thyroid function, and low morning cortisol with an adequate response to high-dose ACTH stimulation, suggesting intact adrenal reserve. Over one year, the tumor size decreased to 1.4 × 1.5 × 1.7 cm with cabergoline therapy.
This case underscores the efficacy of dopamine agonist therapy as first-line management for macroprolactinomas, even in large tumors with significant chiasmal compression. The observed hormonal abnormalities—secondary hypogonadism and growth hormone deficiency—reflect the extensive functional impact of the tumor on pituitary physiology and emphasize the necessity of comprehensive endocrine evaluation. The patient’s favorable response to cabergoline demonstrates that medical management can achieve both biochemical and structural remission, often precluding the need for immediate surgery. From a broader perspective, this case contributes to growing evidence supporting early dopamine agonist initiation and periodic reassessment of pituitary function as key principles for improving outcomes in patients with prolactin-secreting macroadenomas. It also emphasizes the need for a multidisciplinary approach, as the patient was followed by an endocrinologist, neurosurgeon, ophthalmologist, and cardiologist (to monitor for possible Cabergoline adverse effects).

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