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EFFECTS OF METHIMAZOLE ON THYROID GLAND UPTAKE OF 99M TC‐PERTECHNETATE IN 19 HYPERTHYROID CATS
Author(s) -
Fischetti Anthony J.,
Drost Wm Tod,
DiBartola Stephen P.,
Chew Dennis J.,
Schenck Patricia A.,
Meadows Cheyney
Publication year - 2005
Publication title -
veterinary radiology and ultrasound
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.541
H-Index - 60
eISSN - 1740-8261
pISSN - 1058-8183
DOI - 10.1111/j.1740-8261.2005.00040.x
Subject(s) - thyroid , medicine , cats , pertechnetate , methimazole , endocrinology , iodine , hormone , scintigraphy , technetium , nuclear medicine , chemistry , organic chemistry
Nineteen cats with abnormally high serum T 4 concentrations underwent thyroid scintigraphy using technetium‐99m pertechnetate ( 99m TcO 4 ) before and after 36±6 days of methimazole administration (approximately 2.5 mg PO q 12 h). Thyroid‐to‐salivary gland ratios (T:S ratios) and percentage thyroidal uptake of injected radioactivity at 20 and 60 min after injection of 99m TcO 4 were compared before and after methimazole treatment. Serum thyroid stimulating hormone (TSH) concentration was measured before and after methimazole treatment. Quantitatively, there was a positive association between the thyroid uptake of 99m TcO 4 and the serum T 4 before treatment ( r =0.74–0.83). TSH suppression was present when cats were first evaluated for hyperthyroidism. Methimazole treatment did not relieve TSH suppression in 17 cats. Two cats with unilateral thyroid uptake developed bilateral, asymmetric thyroid uptake of 99m TcO 4 after treatment and had the greatest increase in TSH concentration after treatment. Quantitatively, thyroid scintigraphy did not significantly change after methimazole treatment ( P >0.1). Evaluation of serum TSH concentration may be helpful in identifying methimazole‐induced changes in the scintigraphic features of hyperthyroidism in mildly hyperthyroid cats.