Uninhibited thyroidal uptake of radioiodine despite iodine excess in amiodarone-induced hypothyroidism
Iodine excess is associated with a low thyroidal radioiodine uptake due to dilution of the radioisotope by the increased stable iodide pool. We studied thyroidal uptake of radioisotopes in cardiac patients with iodine excess due to amiodarone treatment. /sup 99m/Tc-pertechnetate scintigraphy was performed in 13 patients receiving long term amiodarone therapy. Five patients had a clearly visible thyroid gland, and 8 patients had no or a very faint thyroid image. All patients with positive scans had an increased plasma TSH level, whereas all patients with negative scans had a normal or absent TSH response to TRH. Thyroidal uptake and discharge of 123I were studied in 30 other patients. Group I (n = 11) had normal plasma TSH responses to TRH and no iodine excess, group II (n = 7) had normal TSH responses to TRH and excess iodine from metrizoate angiography in the previous month, group III (n = 7) had normal or decreased TSH responses to TRH while receiving long term amiodarone therapy, and group IV (n = 5) had increased TSH responses to TRH while receiving long term amiodarone therapy. The mean radioiodine uptake value in group I (5.4 +/- 0.8% (+/- SE) at 60 min) was higher than those in group II (2.3 +/- 0.7%; P = 0.009) and group III (0.8 +/- 0.3%; P = 0.0005), but not different from that in group IV (5.3 +/- 1.2%; P = NS). Radioiodine discharge after perchlorate (expressed as a percentage of the 60 min uptake) in group I (10.1 +/- 2.2%) was lower than those in group II (24.9 +/- 10.6%; P = 0.05) and group III (28.8 +/- 5.3%; P less than 0.005), whereas discharge in group IV (58.0 +/- 6.1%) was greater than those in group II (P less than 0.05) and group III (P less than 0.01). In conclusion, 1) thyroid visualization by /sup 99m/Tc-pertechnetate and thyroid radioiodine uptake during iodine excess are decreased in euthyroid and hyperthyroid patients, but preserved in hypothyroid patients.
- OSTI ID:
- 5125189
- Journal Information:
- J. Clin. Endocrinol. Metab.; (United States), Journal Name: J. Clin. Endocrinol. Metab.; (United States) Vol. 2; ISSN JCEMA
- Country of Publication:
- United States
- Language:
- English
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62 RADIOLOGY AND NUCLEAR MEDICINE
BENZOFURANS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BODY
COUNTING TECHNIQUES
DIAGNOSTIC TECHNIQUES
DISEASES
DRUGS
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
ENDOCRINE DISEASES
ENDOCRINE GLANDS
FURANS
GLANDS
HALOGENS
HETEROCYCLIC COMPOUNDS
HORMONES
HOURS LIVING RADIOISOTOPES
HYPOTHYROIDISM
INTERMEDIATE MASS NUCLEI
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IODINE 123
IODINE ISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
NONMETALS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANS
PATIENTS
PEPTIDE HORMONES
PITUITARY HORMONES
RADIOISOTOPE SCANNING
RADIOISOTOPES
RESPONSE MODIFYING FACTORS
SCINTISCANNING
TECHNETIUM 99
TECHNETIUM ISOTOPES
THYROID
TSH
UPTAKE
YEARS LIVING RADIOISOTOPES