[Early recognition of autonomous thyroid tissue by a combination of quantitative thyroid pertechnetate scintigraphy with the free T4 equivalent (author's transl)].

Autonomously functioning thyroid tissue (AFTT) of the circumscribed as well as the disseminated form was found with equal frequency and extent in eumetabolic patients under and over 40 years of age who live in an endemic goitre area. In an area of iodine deficiency this is the most frequent precondition for hyperthyroidism induced by iodine administration. A suspicion of AFTT can be raised in 80% of still euthyroid patients by a combined evaluation of an equivalent to the free T4 (FTE) and an equivalent to the clearance using a quantitative evaluation of the thyroid technetium scan (TcTU). The suppression test not only confirms the autonomy in a qualitative manner but also provides an estimate of the volume of autonomous tissue because the TcTU after suppression strictly correlates linearly with the volume of the AFTT. Since after iodine administration FTE increases proportionally to the volume of AFTT, the procedure can be of some prognostic value: those with autonomous tissue in excess of a "critical" volume will almost certainly develop hyperthyroidism following a certain minimum rate of iodine administration. A prospective study of patients under age 50 whose thyroids contained various amounts of AFTT has shown that prophylactic dietary iodine supplementation will not cause hyperthyroidism to develop provided the additional iodine intake does not exceed 100 micrograms per day.