Endocrine Abstracts

Introduction: TSHomas are rare pituitary tumors that secrete an abnormal amount of a hormone called thyroid-stimulating hormone (TSH). Alternatively given the name thyrotropinoma, only makes up to 1%–2% of all pituitary adenomas. Patients often remain misdiagnosed for years. Many patients undergo treatments that end up destroying the thyroid gland. This case report is to emphasize the rarity of the condition and the importance of diagnosing it early and accurately to ensure timely management and relief of symptoms before perpetual damage is done.

Case description: We present to you a case of a 56 year old lady who presented with anxiety, generalized tiredness and sleeplessness. Blood tests showed: Prolactin levels: 738 mIU/l (l<440 mIU/l), TSH 6.7 (normal 0.27–4.5 mIU/l), T4 36.1 (11–23 pmol/l), T3: 9.15 (3.1–6.8 pmol/l). She was clinically asymptomatic apart from thyroid swelling. She gave a history of previously being treated for prolactinoma followed subclinical hypothroidism having had cabergoline and levothyroxine in the past. Having raised T3 and T4 with raised TSH ringed bells for a high suspicion of TSHoma. Associated Prolactin levels were <1000 mIU/l and was thought to be likely secondary to disconnection hyperprolactenemia (stalk effect). TRH stimulation test to rule out secondary and tertiary causes of thyroid hormone abnormalities was performed which showed flat profile with TSH levels in the range of 5.7–8.11 mIU/L and T4 30–32 pmol/l. T3 supression test with SLR showed TSH levels in the range of 1.9 pmol/l–4.5 pmol/l. Heterophile antibody test to rule out interference with thyroid hormone assays was performed and was found to be negative. Familial dysalbuminemic hyperthyroxenemia test was also negative. Alpha subunit levels were checked showing values of 1.35–2.6 ng/ml. Based on these investigation results a formal working diagnosis of TSHoma was considered likely in contrast to Thyroid hormone resistance. MRI pituitary scan was carried out showing a pitutiary adenoma of 16 mm in size. Patient subsequently had Endoscopic Trans-sphenoidal hypophysectomy with biopsies taken. Histopathology reports confirmed atrophic but viable neoplastic cells expressing prolactin with extensive expression of TSH consistent with pleurihormonal adenoma with somatostain treatment effect.

Discussion: TSHoma is highly under diagnosed. It is important to consider the pitfalls in diagnosis where normal or low alpha sub unit levels could lead to dubious differentials. The use of advance technology i.e functional MRI scans to confirm diagnosis should be carried out early on leading to timely treatment options including radiotherapy and surgery.