A Case of TSH-Secreting Pituitary Adenoma With Unusual Positive Staining for SF1

Abstract Background: TSH-secreting pituitary adenomas are the rarest functional pituitary tumors. While they are often plurihormonal, SF1 positivity (indicating gonadotroph lineage) is unusual. Here we present the rare case of a patient with TSH-secreting pituitary adenoma with staining positive for TSH, GH, prolactin, SSTR2A, PIT-1, and SF1. Clinical Case: Patient is a 42 year-old male with a history of hypogonadotropic hypogonadism (lost to follow-up), who presented with a 5 day history of nausea and vomiting. Vitals were notable for tachycardia to 108 BPM, with BMI 14.8 kg/m2. On physical exam he had enlarged right hemi-thyroid and exophthalmos. Labs were notable for TSH 12.55 μIU/mL (0.27-4.20), Free T4 >7.77 ng/dL (0.80-1.80), Free T3 29.02 pg/mL (2.57-4.43), 8am cortisol 0.9 μg/dL (6.0-18.4), FSH 0.6 μIU/ml (1.5-12.4), LH 0.8 μIU/mL (1.7-8.6), PRL 8.5 ng/mL (4.0-15.2), total testosterone <5 ng/dL (249-836), and IGF-1 88.9 ng/mL (94.4-223.0). MRI showed large lobulated pituitary mass extending into the suprasellar region with mass effect and thyroid US showed enlarged almost completely cystic right hemi-thyroid. The patient was started on methimazole 30mg BID, prednisone 40mg daily, and cabergoline 0.5mg weekly (he declined octreotide). FT4 and FT3 remained significantly elevated despite escalation of cabergoline to 0.5mg 5 days weekly, so the patient was admitted two months after his initial presentation for plasmapheresis followed by thyroidectomy. His hospital course was complicated by post-op meningitis and DI, both successfully treated. Surgical pathology was notable for patchy expression of TSH with rare cells expressing GH and prolactin, SSTR2A positivity, strong nuclear positivity for PIT-1 with negative T-PIT staining, and unusual positivity for SF1. At follow-up he is clinically euthyroid and stable without use of LT4 or HC therapy. Repeat TSH, FT4, ACTH, cortisol, and testosterone are pending. He declines chemotherapy, radiation, and octreotide. Conclusion: This is a rare case of TSH-producing adenoma demonstrating SF1 positivity in addition to TSH, GH, PRL, and PIT-1 expression, in the absence of excess gonadotroph secretion. When such tumors secrete multiple hormones, this has been used as evidence to support the argument that such tumors arise from a stem cell population(1). However, the implications for our patient remain unclear. References: (1) Tordjman et al. Plurihormonal Pituitary Tumor of Pit-1 and SF-1 Lineages, with Synchronous Collision Corticotroph Tumor: a Possible Stem Cell Phenomenon. Endocr Pathol. 2019 Mar;30(1):74-80.