Endocrine Abstracts

Introduction: Secondary hyperthyroidism due to thyrotropin-secreting pituitary adenoma (TSHoma) is rare. Coexistence of TSHoma and primary thyroid disease that could lead to hyperthyroidism is even more unusual.

Case report: A 28-year-old female with longstanding and worsening symptoms of hyperthyroidism was admitted to the hospital. Free-T₄ (32.89 pmol/l) and free-T₃ (6.38 pg/ml) were elevated with moderately increased TSH level (5.997 μIU/ml) suggesting secondary hyperthyroidism. Diagnosis was confirmed by dynamic testing with TRH, that showed no rise in TSH, and MRI revealed a pituitary microadenoma. At the ultrasound thyroid volume was normal, with no nodules nor enhanced blood flow, but with decreased echogenicity and heterogeneous echotexture. Antithyroid antibodies were negative and 24 h iodine uptake was increased (76%). Somatostatin analogue, administered before transsphenoidal neurosurgery, resulted in a moderate improvement of symptoms and hormonal results. After successful tumour removal clinical and laboratory signs of hyperthyroidism resolved. However, a month after neurosurgery symptoms of thyrotoxicosis recurred with elevated fT₄:32.94 pmol/l, fT₃:10.17 pg/ml and suppressed TSH<0.001 μIU/ml. No eye signs, neck pain or goiter were present. Iodine uptake was low (3.5%) and thyroid was hypervascular and remarkably hypoechoic at ultrasound. TPO-ab (91.2 IU/ml) and TG-ab (10.11 IU/ml) titers increased but TR-ab were negative. We diagnosed iodine-induced hyperthyroidism in a patient with preexisting silent thyroid disease (autoimmune thyroiditis) in whom povidone-iodine antiseptic solution was used during neurosurgery. Patient was treated with thiamazole and prednisone with a prompt improvement. Five months after surgery she was well, euthyroid, with no residual adenoma on MRI and a normal response of TSH secretion in TRH test (TSH 0’:1.24 μIU/ml, 60’:7.66 μIU/ml).

Conclusions: Exposure to topical iodine-containing solutions could lead to iodine-induced thyroid dysfunction in susceptible patients with preexisting thyroid disease. In such patients with coexisting pituitary adenomas usage of iodine-based antiseptic solutions should be avoided.