Thyroid Color Flow Doppler Sonography: An Adjunctive Tool for Differentiating Patients with Inappropriate Thyrotropin (TSH) Secretion due to TSH-Secreting Pituitary Adenoma or Resistance to Thyroid Hormone

Background: Thyrotropin (TSH)-secreting pituitary adenoma (TSHoma) and resistance to thyroid hormone (RTH) are two forms of inappropriate TSH secretion. Thyroid blood flow is largely TSH dependent. Objective: To assess whether thyroid blood flow may help to differentiate TSHoma and RTH. Design: Intrathyroidal color flow Doppler sonography (CFDS) pattern and peak systolic velocity (PSV) were assessed at baseline and during T3 suppression test on eight consecutive patients with TSHoma and 10 with RTH. Main outcome: All controls had CFDS pattern 0. Three RTH patients had pattern I and seven had pattern II. Two TSHoma patients had pattern I, five had pattern II, and one had pattern III. PSV at baseline was 3.8 1.3 cm/s in controls, 8.8 2.5 cm/s in RTH, 11.1 2.7 cm/s in TSHoma (p 0.0003 vs. controls, p 0.087 RTH vs. TSHoma). After T3 suppression test, PSV values were lower in RTH than in TSHoma (4.6 1.8 vs. 7.7 2.6 cm/s, p 0.008). PSV values and CFDS pattern normalized in nine and eight RTH patients, respectively, after T3 suppression test; conversely, only one TSHoma patient had a normalization of PSV values, and none had a normalization of CFDS pattern (p 0.003 vs. RTH). Conclusions: Both RTH and TSHoma have increased CFDS pattern and PSV values; however, after T3 both parameters normalized in most patients with RTH but not in those with TSHoma. Accordingly, CFDS pattern and PSV are adjunctive tools to differentiate these two forms of inappropriate TSH secretion.