MON-414 The Case of a Dual-Secreting Pituitary Macroadenoma

Abstract

Introduction: Pituitary adenomas are estimated to occur in 17% of the population (1 in 600 persons).1 One-half of pituitary adenomas secrete a distinct hormone, most often prolactin, GH or ACTH.1 Prolactinomas are the most common, 50% of functional pituitary tumors and 40% of pituitary tumors overall.1 Exceedingly rare are dual-secreting pituitary adenomas. We aim to describe a pituitary macroadenoma secreting both prolactin and ACTH with significant mass effect. Clinical Case: An 87-year-old female was seen in Endocrine clinic for bitemporal hemianopsia and fatigue in October 2017. A brain MRI revealed a 2.0 x 1.1 x 1.2 cm pituitary mass displacing the optic chiasm and left optic nerve. She denied any headaches, galactorrhea, weight or appetite changes. Her physical exam was only notable for visual field defects. Her prolactin was 591 ng/mL (n 5-23 ng/mL) and 395 ng/mL after a dilution test. Her ACTH was 103 pg/ml (n 6-58 pg/mL) and cortisol 15 ug/dl at baseline. After a low-dose (1 mg) dexamethasone suppression test, ACTH was 32 pg/ml and cortisol was 5.1 ug/dl (cutoff 1.8 ug/dl). A high-dose (8 mg) dexamethasone test suppressed ACTH to 3.7 pg/mL and cortisol to 0.9 ug/dl. Her TSH was 0.64 uIU/mL (n 0.30-4.50 uIU/mL) with a total T4 of 0.6 ng/dL (n 0.6-1.5 ng/dL). The patient was deemed a poor Neurosurgical candidate due to her age and comorbidities. She was started on Levothyroxine and Cabergoline. Over time with medical management, her vision loss and fatigue improved. Her prolactin level reduced from 591 ng/mL to 209 ng/mL after 2 months. On repeat brain imaging in February 2018, the macroadenoma was stable in size. Discussion: Our case is unique as it describes a pituitary macroadenoma with concurrent secretion of prolactin and ACTH. She presented with subclinical Cushing’s disease given her test results, no symptoms, and normal exam. Gradual growth of the adenoma led to pituitary compression and a secondary hypothyroidism. While the adenoma was stable in size, resolution of her visual field defect indicates some treatment response. Dual-secreting pituitary adenomas are rare. In a 6-year study at UCSF, 22 of 593 patients diagnosed with pituitary adenomas had dual GH and prolactin secretion (3.7%).2 As for coexistent ACTH and prolactin tumor secretion, very few cases have been reported.3Conclusion: Neuroendocrine tumors have the potential for significant morbidity due to potent endocrine effects and critical mass effect as seen in our patient.1 Early diagnosis and treatment is critical to reduce morbidity and mortality of this disease.