An Atypical Case of TSH-Secreting Pituitary Adenoma in a Patient Presenting With Low Libido and Insomnia

Background: TSH-secreting pituitary adenoma is an incredibly rare cause of hyperthyroidism. Most patients with TSHomas present with clinical hyperthyroidism, but some patients may have atypical signs. Here we present the case of a patient who had been suffering from low libido and insomnia who was found to have secondary hyperthyroidism from a TSH-secreting pituitary adenoma. Clinical Case: A 47-year-old man presented with complaints of progressive headache, fatigue, depression, insomnia, low libido and erectile dysfunction. After questioning, he noted the presence of intentional tremor for more than 5 years. He denied anxiety, palpitations, heat intolerance, hyper defecation, proximal muscle weakness, local compressive symptoms of the neck and ocular symptoms. Physical exam was notable for fine tremor and mild thyromegaly, but otherwise patient had no evidence of anxiety, exophthalmos, hyperreflexia or diaphoresis. The patient was found to have a normal free testosterone (46 pg/mL, n 30-140 pg/mL) but had an elevated TSH (6.302 IU/mL, n 0.4-5 IU/mL), elevated Free T4 (3.6 ng/dL, n 0.6-1.2 ng/dL) and an elevated T3 (422 ng/dL, n 73-178 ng/dL). Further lab work revealed elevated alpha-subunit (4.4 ng/mL, n <0.5 ng/mL) suggestive of TSH-secreting pituitary adenoma. Prolactin and IGF-1 levels were normal. Patient had an MRI pituitary which showed a 2.3 cm sellar mass abutting the optic chiasm without involvement of the cavernous sinus. Patient proceeded to trans-sphenoidal resection. Post-operatively, TSH had dropped from 6.534 to 0.002 IU/mL (n 0.4-5 IU/mL) and Free T4 had dropped from 3.1 to 0.5 ng/dL (n 0.6-1.2 ng/dL). Interestingly, immunohistochemical staining was negative for TSH but the specimen did show histologic features characteristic of TSH-producing adenoma including extensive stromal fibrosis and nuclear pleomorphism. Patient was seen in clinic post-operatively where he noted a dramatic improvement in his headache and insomnia. He did show signs of hypothyroidism including constipation and weight gain. Patient was started on levothyroxine 75 mcg PO daily. Conclusion: This demonstrates the case of a patient with a TSH-secreting pituitary adenoma who presented with minimal thyrotoxic symptoms despite elevated thyroid hormones. Patients with this condition may present with atypical symptoms, thus requiring clinicians to have a high index of suspicion for this rare tumor. References: (1) Beck-Peccoz, P., Lania, A., Beckers, A. et al. 2013 European thyroid association guidelines for the diagnosis and treatment of thyrotropin-secreting pituitary tumors. Eur Thyroid J 2013; 2:76. (2) Cossu, G., Daniel, R.T., Pierzchala, K. et al. Thyrotropin-secreting pituitary adenomas: a systematic review and meta-analysis of postoperative outcomes and management. Pituitary 2019; 22:79.