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Thyroid suppression test with L‐thyroxine and [ 99m Tc] pertechnetate
Author(s) -
Ratnos Celso D.,
ZantutWittmann Denise E.,
Tambascia Marcos A.,
Assumpção Lígia,
Etchebehere Elba C. S. C.,
Camargo Edwaldo E.
Publication year - 2000
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1046/j.1365-2265.2000.00898.x
Subject(s) - euthyroid , medicine , pertechnetate , thyroid , technetium , endocrinology , nuclear medicine , prospective cohort study , gastroenterology , thyroid disease , thyroid nodules , graves' disease
Summary OBJECTIVE The thyroid suppression test is still used in some centres as an adjunt in the diagnosls of autonomous functioning thyroid nodules. With the purpose of minimizing the disadvantages of the original T3 suppression test, we have evaluated the efficacy of a method using L‐thyroxine as TSH suppression agent and [ 99m Tc] pertechnetate as radio‐pharmaceutical. DESIGN Open nonrandomized prospective study MATERIALS AND METHODS A control group of 15 normal volunteers (11 males, 4 females; 21–35 years, mean 26–4 years) and a patient group of 20 patients (18 females, 2 males: 27–83 years, mean 53.6 years) divided into 4 subgroups, were studied: 7 patients with autonomous functioning nontoxic nodules, 3 with autonomous functioning toxic nodules, 7 with Graves disease and 3 with nonautoimmune diffuse toxic goitre. Baseline thyroid uptake and imaging were begun 20 minutes after an intravenous injection of 370 MBq (10mCi) of [ 99m Tc] pertechnetate. This was followed by a single daily intake of 2μg/kg of L‐thyroxine, for 10 days. Thyroid imaging and uptake were then repeated. RESULTS In the control group [ 99m Tc] pertechnetate uptake after L‐thyroxine suppression had a mean reduction of 75.8 ± 7.69% (58–47%) in comparison to the baseline level. All subjects were euthyroid by clinical and laboratory criteria and none complained of side‐effects, despite significant suppression of TSH levels. In the patient group, thyroid uptake after suppression decreased in 10 patients (maximum reduction 39%), was unchanged In 2 patients and increased in the remaining 8 patients. CONCLUSION The method described was efficient for demonstration of autonomous thyroid tissue, since none of the patients showed significant reduction of thyroid uptake after L‐thyroxine suppression compared with the control group. This test was as effective as the original T 3 suppression test, but more convenient to the patient: no side‐effects, ease of hormonal intake, low dosimetry and short stay in the nuclear medicine laboratory.