The presence of an elevated cardiac index and development of atrial
fibrillation led to the testing of thyroid function. The results were
consistent with pronounced thyrotoxicosis, with a total thyroxine
concentration of 20.8 μg/dL (normal, 5.0 to 10.6 μg/dL), free
thyroxine index of 6.0 ng/dL (normal, 1.0 to 2.2 ng/dL), and
thyroid-stimulating hormone < 0.04 μIU/mL (normal, 0.10 to 6.3μ
IU/mL). On examination, the thyroid gland was small without any
irregularities. She did not have any stare, lid lag, or proptosis.
Auscultation of the lungs revealed clear lung fields, and her cardiac
sounds were notable for splitting of both S1 and
S2. In addition, she had extensive pitting edema
in both lower extremities. A mild fine tremor was observed in both
hands, as was mild hyperreflexia. Titers of antithyroglobulin (positive
at a titer of 1:2,560; normal, < 1:10), antiperoxidase (556 IU/mL;
nonreactive, < 1.5), and thyroid-stimulating hormone (163%; normal,< 130% of basal activity) antibodies were elevated. As a result of
these findings, a diagnosis of Graves’ disease was made.