Endocrine Abstracts

Patients with inappropriate TSH syndrome have elevated serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations and normal or slightly elevated serum thyroid stimulating hormone (TSH) level. Inappropriate TSH syndrome include generalized resistance to thyroid hormone (GRTH), pituitary resistance of thyroid hormone (PRTH) and TSHoma.

We report here three cases that the first patient has GRTH, the second has TSHoma and third patient has PRTH. Patient with GRTH has goitre and normal TSH and high serum levels of FT3 and FT4. The patients with GRTH and PRTH have sufficient TSH respond to TRH stimulation test. After T3 suppression test, patient with GRTH has unelevated SHBG but ferritin level was elevated. Whereas patient with PRTH has elevated SHBG and elevated ferritin levels. The patient with GRTH and the patient with PRTH has not pituitary adenoma on pituitary MRI. Patient with TSHoma has inappropriate TSH secretion, pituitary adenoma on pituitary MRI and elevated α subunit/TSH molar. The patient with TSHoma has insufficient TSH respond to TRH stimulation test.

As a result; if the relation between T3, T4 and TSH can not be explained, GRTH, PRTH and TSHoma diseases should be kept in mind and the necessity tests for differential diagnosis should be made for inappropriate TSH syndrome.