RT Journal
A1 Grund FM, Niewoehner CB
T1 HYperthyroxinemia in patients receiving thyroid replacement therapy
JF Archives of Internal Medicine
JO Archives of Internal Medicine
YR 1989
FD April 1
VO 149
IS 4
SP 921
OP 924
DO 10.1001/archinte.1989.00390040119024
UL http://dx.doi.org/10.1001/archinte.1989.00390040119024
AB • Eleven patients, with a history of hypothyroidism, who had hyperthyroxinemia and an elevated free thyroxine index but normal serum triiodothyronine concentrations on levothyroxine replacement underwent levothyroxine dose reduction at three-month intervals until the free thyroxine index fell into the normal range. All were clinically euthyroid throughout. Normalization of the thyrotropin response to thyrotropinreleasing hormone occurred concomitantly, indicating correction of subtle hyperthyroidism. The mean thyroxine dose decreased from 161 μg/d (2.06 μg/kg) to 120 μg/d (1.51 μg/kg). The resting heart rate fell in eight of 11 patients (P<.02). The left ventricular ejection fraction decreased in eight of 11 patients, although the decrease was not statistically significant. Considering the sensitivity of pituitary, cardiac, and bone tissue to even a small excess of thyroxine over time, hyperthyroxinemia associated with an elevated free thyroxine index should be corrected even in patients taking levothyroxine replacement who are clinically euthyroid and whose serum triiodothyronine concentrations are within normal limits.(Arch Intern Med 1989;149:921-924)