THYROID STIMULATING HORMONE (TSH) SECRETING PITUITARY ADENOMA: A RARE CAUSE OF THYROTOXICOSIS.

Introduction: Thyroid stimulating hormone secreting pituitary adenoma (TSHoma) is a rare cause of thyrotoxicosis, which manifests with features of thyrotoxicosis along with neurological manifestations of pituitary tumour. Biochemically, it is characterized by elevated thyroid hormone (T3 and T4) levels with unsuppressed TSH levels. It accounts for 1-2% of all pituitary adenomas. Mixed TSHomas account for 30% of these cases, among which mixed TSHoma/LH(luteinizing hormone)oma is very rare (<2%). We report a case of mixed TSHoma/LHoma, who was successfully treated with pre-operative Somatostatin analogues followed by Endoscopic Transphenoidal surgery for resection of pituitary adenoma. Case report: A 35 years old, male presented to our hospital in September 2017 with complaints of headache, decreased vision in both eyes, palpitations, excessive sweating, tremors of the hands and increased frequency of loose stools since 8 months. He had bilateral gynaecomastia and decreased libido since 6 months. On evaluation, he was found to have Free T3: 7.5pg/ml (1.45-3.48), Free T4: 2.1ng/dl (0.75-1.85), TSH: 25.31mU/l (0.27-4.2), Prolactin: 31ng/ml (4.1-15.4). MRI Brain showed pituitary macroadenoma of size 2.7?3.4?3.6 cm with suprasellar extension and displacement of optic chaisma laterally. He was treated initially with daily subcutaneous Octreotide for 2 months followed by a single dose of long acting Octreotide LAR. One week after starting Octreotide, his symptoms improved and Free T3 was decreased to 5.42pg/ml, Free T4 to 1.75ng/dl and TSH came down to 16.34mU/l. Then 2 months later, Free T3 was 1.7pg/ml (2.1-4.2), Free T4 was 0.81ng/dl (0.8-2.7), TSH was 0.98mU/l (0.35-4.5). His 8am cortisol was 5.5mcg/dl, LH was 2.61U/l, FSH was 3.63U/l, Testosterone was 1.59ng/ml, IGF-1 was 149ng/ml and Prolactin was 20.2ng/ml. USG neck showed normal sized thyroid gland with a tiny colloid cyst of size 5?3mm in the right lobe of thyroid. Repeat MRI Brain showed pituitary macroadenoma measuring 2.2?2?2.6 cm with suprasellar extension, displacing the optic chaisma superiorly and partial encasement of bilateral cavernous ICA. He was treated with Endoscopic Transphenoidal surgery for resection of pituitary adenoma, along with peri-operative steroid coverage and levothyroxine supplementation. Post-operative period was uneventful, his steroids were tapered and stopped. The histopathology and immunohistochemistry report were s/o TSHoma. He was discharged 1 week later with levothyroxine supplementation. Conclusion:TSHoma should always be considered in patients who present with signs and symptoms of thyrotoxicosis, but with unsuppressed TSH levels in presence of elevated thyroid hormone levels, especially in those who have features of mass effects of pituitary tumour. Its recognition is important avoid unnecessary anti-thyroid drugs and thyroid ablative therapies, which can have a detrimental effect on the pituitary mass.