Relationship between thyroid volume and serum thyroglobulin during long-term suppression with triiodothyronine in patients with diffuse non-toxic goitre

Twenty-five patients with non-toxic diffuse goitre were studied during and after 12 months of treatment with 60 micrograms triiodothyronine daily in order to see whether a correlation could be found between the reductions of thyroid volume, using ultrasonic scanning, and serum thyroglobulin. Thyroid function tests and thyroid volume determination were performed before treatment and after 3, 6 and 12 months of therapy in 19 patients (group 1). In patients of group 2 (n = 19) the same tests were performed at the end of 12 months treatment and 6 and 12 months after withdrawal. Before treatment all patients had a significantly increased thyroid volume compared to controls matched according to sex, age and body weight (P less than 0.001). Serum thyroglobulin was elevated compared to controls (P less than 0.02), with a significantly positive correlation to the thyroid volume (Spearmann's Rho = 0.52, P less than 0.02). Both serum thyroglobulin and thyroid volume decreased during treatment in the majority of the patients, concomitantly in approximately half of them. After withdrawal of treatment (group 2) serum thyroglobulin showed a median increase of 54% after 6 months and remained unchanged thereafter, whereas the thyroid volume was unchanged after 6 months. These findings might support the concept that the regulation of thyroid growth and of protein synthesis and degradation might be determined by different factors.