DETERMINATION OF THE AUTONOMOUSLY FUNCTIONING VOLUME OF THE THYROID

The aim of this work was to determine the autonomously functioning vol ume in euthyroid and hyperthyroid goitres for prognostic and therapeut ic purposes. To this end, various groups of patients were selected: in dividuals without evidence of thyroid disease, euthyroid patients with diffuse goitre of normal structure and function, euthyroid patients w ith evidence of autonomy and patients with hyperthyroidism due to auto nomy. In all of them the thyroid uptake of technetium-99m was determin ed under exogenous suppression (TcU(s)) in the euthyroid state and und er endogenous suppression (TcU) in the hyperthyroid state. It was demo nstrated that: 1. In patients with unifocal autonomy the TcU(s) and Tc U correlated linearly with the autonomous volume delineated and measur ed by sonography. 2. A nearly identical result was obtained if the mea n autonomous volume in individuals without thyroid disease of 2.2 +/- 1.1 ml calculated by TcU(s)/TcU x total thyroid volume was used as a b asis. 3. The critical autonomous volume, i.e. the volume at which hype rthyroidism will occur, was found to be 16 ml at a cumulated sensitivi ty and specificity of > 0.9. The method can be used to select patients for definitive treatment before hyperthyroidism occurs and to measure the autonomously functioning volume independent of its distribution w ithin the thyroid for treatment with radioiodine. The method is easy t o perform and is also an example of how a relative parameter of a func tion can be converted into an absolute parameter of a functioning volu me.