Increased serum thyroglobulin concentrations and impaired thyrotropin response to thyrotropin-releasing hormone in euthyroid subjects with endemic goiter in Sicily: their relation to goiter size and nodularity
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Serum thyroglobulin (Tg), T4, T3, FT4, FT3, TSH concentrations and TSH response to iv TRH (ΔTSH) were measured in 56 consecutive patients with (multi) nodular goiter from a severily iodine-deficient endemic goiter area in Northeastern Sicily and in 11 non goitrous euthyroid individuals living in the same area. Serum Tg concentrations were sharply increased in goitrous subjects (453 ± 476 ng/ml) and related to thyroid size and the presence of nodules (χ2 = 43.5, p < 0.0005). Serum TSH levels measured in goitrous patients (2.1 ± 0.9 μU/ml) were significantly lower than those measured in nongoitrous iodine deficient subjects (3.1 ± 0.9 μU/ml, p <0.001) and decreased with increasing goiter size and nodularity (χ2 = 27.3, p<0.05). A similar pattern was shown by the analysis of the Δ TSH (χ2 = 43.1, p<0.0005). These results suggest that at least a part of the largest and multinodular goiters become autonomously functioning with duration and growing in size. In 13 goitrous patients with absent or impaired response to TRH, a significant direct relation was apparent between log-Tg and goiter size and nodularity (r = 0.64) with an inverse relationship between serum FT3 and Δ TSH (r = 0.73). A computed program analysis based on the combination of different independent variables (x) including age, thyroid size and nodularity, serum TSH, log-Tg and FT3, indicated the existence of a significant negative relationship between these variablesand the TSH response to TRH (r = 0.75, p = 0). This confirms the limited clinical significance of the impaired TSH response to TRH in patients with multinodular goiters and gives an explanation for the not infrequently observed ineffectiveness of suppressive treatment with thyroid hormones.
Key-wordsThyroglobulin endemic goiter thyroid autonomy TSH response to TRH iodine deficiency
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