Determination of the autonomously functioning volume of the thyroid.

The aim of this work was to determine the autonomously functioning volume in euthyroid and hyperthyroid goitres for prognostic and therapeutic purposes. To this end, various groups of patients were selected: individuals without evidence of thyroid disease, euthyroid patients with diffuse goitre of normal structure and function, euthyroid patients with evidence of autonomy and patients with hyperthyroidism due to autonomy. In all of them the thyroid uptake of technetium-99m was determined under exogenous suppression (TcUs) in the euthyroid state and under endogenous suppression (TcU) in the hyperthyroid state. It was demonstrated that: 1. In patients with unifocal autonomy the TcUs and TcU correlated linearly with the autonomous volume delineated and measured by sonography. 2. A nearly identical result was obtained if the mean autonomous volume in individuals without thyroid disease of 2.2 +/- 1.1 ml calculated by TcUs/TcU x total thyroid volume was used as a basis. 3. The critical autonomous volume, i.e. the volume at which hyperthyroidism will occur, was found to be 16 ml at a cumulated sensitivity 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 within the thyroid for treatment with radioiodine. The method is easy to perform and is also an example of how a relative parameter of a function can be converted into an absolute parameter of a functioning volume.