Endocrine Abstracts

Introduction: Prolactinomas are the most common hormone-secreting pituitary tumors, accounting for up to 40% of pituitary adenomas. They are classified into microprolactinomas (<10 mm), macroprolactinomas (≥10 mm), and giant prolactinomas (≥40 mm). Symptoms may arise from hyperprolactinemia or mass effect. Differential diagnoses for hyperprolactinemia include physiological states, medications, hypothyroidism, and non-functioning adenomas. We report a case of a giant prolactinoma with central hypothyroidism and hypogonadism, showing a remarkable response to medical therapy.

Case Presentation: A 45-year-old male was evaluated for ejaculatory dysfunction. Initial testing revealed low testosterone (1.70 nmol/l), prompting pituitary hormone assessment:

• Prolactin: 220,948 mU/l

• FSH: 1.53 IU/l

• LH: 1.10 IU/l

• TSH: 0.96 mU/l

• Free T4: 7.5 pmol/l

• Cortisol: 327 nmol/l

He reported fatigue, aches, headaches, visual blurring, dizziness, and low libido but denied galactorrhea, rhinorrhea, or erectile dysfunction. Past medical history included atrial septal defect, pulmonary valve stenosis, and chronic hepatitis B. Visual fields by confrontation were initially normal. MRI revealed a large pituitary macroadenoma remodeling the clivus, displacing the optic chiasm, encasing the left internal carotid artery, and invading both cavernous sinuses. The patient denied any CSF leak. He was started on Cabergoline (250 mg twice weekly) and referred urgently to the Pituitary MDT and Ophthalmology. Formal testing revealed grossly depressed visual fields bilaterally, and the patient was advised not to drive. Baseline echocardiography was stable.

After one month:

• Prolactin: 19,526 mU/l

• TSH: 1.75 mU/l

• Free T4: 10.4 pmol/l

• Cortisol: 396 nmol/l

• Testosterone: 2.19 nmol/l

Cabergoline was uptitrated to 500 mg TDS, reducing prolactin to 2,000 mU/l, and is being increased to 1 mg BD. Testosterone replacement was initiated. Levothyroxine was started for central hypothyroidism. The patient is awaiting a repeat MRI scan to assess tumor size and further guide management.

Conclusion: This case demonstrates the potential for dramatic prolactin reduction and symptomatic improvement in giant prolactinomas with high-dose dopamine agonists alone. Surgery may be avoidable even in large, invasive tumors. Treatment goals include rapid tumor shrinkage, visual recovery, and full hormonal restoration.