Coexistence of Pituitary Adenoma Causing Acromegaly and Medullary Thyroid Cancer

Background: We present a case of coexisting acromegaly and medullary thyroid cancer. As both conditions are rare, the association raises the possibility of causality (non-genomic) as opposed to pure coincidence. Clinical Lesson: A 73 year-old man presented to our clinic with an incidental finding of a left thyroid nodule. The patient underwent an ultrasound-guided fine needle aspiration biopsy which revealed medullary thyroid carcinoma. Shortly afterward, the patient underwent a total thyroidectomy with bilateral cervical lymph node dissection. The patient tested negative for mutations involving RET exons 8, 10, 11, 13, 14, 15, and 16. On initial presentation, the patient was also noticed to have an appearance typical of acromegaly, with spade-like hands and characteristic acromegalic facial features, including prognathism and macroglossia. These findings were long-standing. He was found to have elevated IGF-1 (121.4 nmol/L, reference range 6.1 - 26.9 nmol/L) and hyperprolactinemia (78.2 mcg/L, reference range 2.7 - 16.9 mcg/L). His growth hormone (GH) levels did not suppress following a 75 g oral glucose tolerance test. Magnetic resonance imaging of the sella turcica revealed a prominent pituitary gland and stalk with a rightward deviated infundibulum, with a suspected 1.1 cm left-sided pituitary macroadenoma. The patient declined surgical management, and he was instead managed medically with octreotide. Conclusion: Coexistance of GH-producing pituitary adenoma and medullary thyroid cancer is a rare occurrence. We identified ten cases previously described in the literature. Specifically, this is the second reported case of a patient presenting with both medullary thyroid cancer and pituitary adenoma causing acromegaly. The advanced acromegalic phenotype suggested long standing disease and therefore prolonged tissue exposure to elevated levels of IGF-I. Although acromegaly is more commonly associated with nodular goiter of follicular-cell origin, the possibility of a thyroidal C-cell neoplasm must be entertained especially if GLP-1 agonist therapy is being considered for the treatment of hyperglycemia.