A Rare Case of a Plurihormonal Pituitary Adenoma

Background: Pituitary adenomas are usually benign tumors that arise from adenophypophyseal cells and produce one or two types of hormones. Plurihormonal adenomas are a rare subtype that produce two or more hormones and represent less than 1% of all pituitary adenomas. Clinical Presentation: A 76-year-old female presented for evaluation of abnormal thyroid function test results. She was found to have an elevated free T4 of 1.92 ng/dL and total T4 of 14.4 ug/dL with an inappropriately normal TSH of 2.11 uIU/mL. Physical examination was significant for tachycardia, tremors, diaphoresis, coarse facial features, and enlarged hands. Further biochemical evaluation of her pituitary hormone levels demonstrated an elevated prolactin (PRL) of 237.2 ng/mL, elevated insulin-like growth factor 1 (IGF-1) of 787 ng/mL, normal morning ACTH of 47 pg/mL, normal morning cortisol of 17.0 ug/dL, an inappropriately suppressed FSH of <5.0 mIU/mL, an elevated alpha subunit of pituitary glycoprotein hormones (PGH) of 6.9 ng/mL, and an elevated free T4 of 3.5 ng/dL by equilibrium dialysis. She underwent an MRI of the pituitary and brain which demonstrated a pituitary adenoma measuring 1.2 x 1.3 x 1.8 cm with a portion herniating into the sella turcica with no mass effect of the optic chiasm. A formal visual field examination was normal. The patient underwent workup for Cushing’s Disease with a low dose overnight dexamethasone suppression test, resulting in an appropriate response with an 8 AM cortisol of <1.0 ug/dL. Glucose suppression test confirmed the diagnosis of acromegaly with growth hormone at 120 minutes of 19.90 ng/mL. Neurosurgery performed a trans-sphenoidal pituitary adenoma resection. Thyroid function tests on post-operative day 4 demonstrated a suppressed TSH of 0.01 uIU/mL and an elevated free T4 of 2.30 ng/dL. Histological evaluation revealed dual expression of transcription factors pituitary-specific positive transcription factor 1 (PIT1) and steroidogenic factor 1 (SF1) as well as PRL, GH, TSH and FSH expression. Immunostaining for LH and ACTH were negative. Post-operative IGF-1 and GH levels were 106 ng/mL and 0.51 ng/mL at 17 weeks, respectively. Post-operative TSH normalized to 0.82 uIU/mL, free T4 normalized to 1.04 ng/dL, and PRL normalized to 8.1 ng/mL at 12 weeks. The patient remained symptom free after successful surgical resection. Discussion: Our case demonstrates the clinical course of a unique patient with clinical and biochemical manifestations of thyroid dysfunction and acromegaly with a pituitary adenoma immunoreactive for GH, TSH, FSH, and PRL. The co-secretion of GH, TSH, PRL, and FSH as well as positivity for the alpha-subunit is extremely unusual. This case emphasizes the importance of considering pituitary abnormalities as a cause for abnormal thyroid function tests.