Thyroid hormone resistance (THR) and pituitary TSH-secreting adenomas (TSHoma) are both characterised by increased serum free thyroid hormone levels and normal TSH concentrations. Differentiation of the two syndromes is a clinical challenge, and relies on the suppression (TRH) or lack of suppression (TSHoma) of TSH-dependent parameters and on the presence of germinal mutations in the thyroid hormone receptor beta 1 gene in patients with THR. Thyroid blood flow, evaluated using color flow Dopller sonography (CFDS) depends on TSH receptor stimulation; in fact, it is increased in patients with Graves disease and absent in those with thyrotoxicosis factitia.
The aim of the study was to assess whether CFDS might help in differentiating patients with THR or TSHoma. CFDS was performed in 6 patients with THR and 6 patients with TSHoma during T3 suppression test at 50, 100 and 200 mcg Titre. Patients with THR or TSHoma did not differ as serum TSH levels, CFDS pattern and intraparenchiaml peak systolic velocity (PSV). Mean PSV values reduced from 9.2±1.6 cm/s to 3.7±0.5 cm/s in patients with THR and from 11.3±3.3 cm/s to 7.3±2.6 cm/s in patients with TSHoma (P<0.005) during T3 suppression test. PSV values and CFDS pattern reduced to the normal range in 5 patients with THR and in 1 patient with TSHoma (P<0.05).
In summary, the present study shows that 1) thyroid blood flow is increased in patients with THR or TSHoma, 2)CFDS pattern and intraparenchymal PSV values reduced to the normal range in most patients with THR but not in those with TSHoma. In conclusion, thyroid CFDS may represent an adjunctive tool for differentiating patients with THR or TSHoma.
01 - 05 Apr 2006
European Society of Endocrinology