Thyrotropin-Secreting Pituitary Adenoma Successfully Treated With Cabergoline

Background: Thyrotropin secreting pituitary adenomas (TSH-oma) account for less than 1% of pituitary adenomas and are a rare cause of hyperthyroidism. In this case, we describe the safe use of cabergoline with the subsequent achievement of euthyroid levels and the resolution of symptoms. Clinical Case: A 67-year-old female with a presumed history of hypothyroidism for the last 3 years managed with Armour thyroid was referred for fatigue associated with palpitations, intermittent diarrhea, insomnia, and anxiety. Her TSH was noted to be suppressed at that time, and her Amour thyroid was changed to Levothyroxine 25 mcg daily, which was eventually stopped as her symptoms persisted. Follow-up thyroid function tests (TFTs) showed elevated TSH (8.60 µU/mL, reference range 0.340 - 5.600 µU/mL), and elevated free T3 (10.8 pg/mL, reference range 2.7-4.7 pg/mL) and free T4 (2.0 ng/dL, reference range 0.8-1.5 ng/dL) levels. Further laboratory workup including basal prolactin, LH, FSH, hCG α-subunit, IGF-1, and ACTH levels were within the normal range. Physical examination showed diffuse thyroid enlargement. An I-123 thyroid uptake and scan showed uniform uptake throughout the gland with no focal hyperintense areas. A dedicated pituitary MRI was performed and revealed an 8 mm microadenoma in the posterior left adenohypophysis. The patient wanted to avoid any invasive treatment and refused trans-sphenoidal surgery and medical therapy was chosen. Unfortunately, using a somatostatin analog as part of the standard medical treatment was not an option due to the high cost and lack of insurance coverage. For these reasons, a trial of cabergoline was started to suppress TSH secretion. Atenolol 25 mg daily was added temporarily for the management of her sympathetic symptoms. On periodic follow-up, her symptoms gradually subsided, and TFTs remained within normal limits. Treatment was continued for one year. Conclusion: Clinical manifestations of hyperthyroidism with biochemical evidence of elevated thyroid hormone levels and TSH levels should raise a strong suspicion for central or secondary hyperthyroidism due to TSH secreting pituitary adenoma. Cabergoline might represent an effective alternative form of medical treatment for TSH-oma in certain situations where the first line therapeutic options are refractory, contraindicated, or declined.