A 42-year-old woman complains of anxiety, unexplained weight loss, and palpitations
that started about 3 weeks earlier. She denies fever, trauma, and new
stress. She has a history of several urinary tract infections for which imaging
failed to reveal any predisposing factors; all were successfully treated with
medication. The remainder of the history is unremarkable.
The patient is a nervous, mildly obese woman whose clothes appear to be
too large for her. Temperature is 37.2C (99F); heart rate, 103 beats per
minute and normal rhythm; respiration rate, 24 breaths per minute; and blood
pressure, 148/96 mm Hg. Mild exophthalmos is evident, although the patient
denies any changes in visual acuity. The thyroid gland is smooth and diffusely
enlarged; no adenopathy is noted. Lungs are normal. Results of a neurologic
examination are also normal. The patient's thyroid-stimulating hormone (TSH)
level is markedly low.
Which diagnostic test would you order next—and why?
WHICH TEST—AND WHY: The patient's symptoms and low TSH level suggest a
thyrotoxic state. A nuclear medicine thyroid study can help distinguish between
the various kinds of thyrotoxic states:
- Homogeneous enlargement of the thyroid gland is most
consistent with Graves' disease.
- An enlarged gland with a heterogeneous appearance
suggests a toxic multinodular goiter.
- A focal area of increased activity within the gland—with
suppression of activity in the remainder of the gland—is
most consistent with a toxic adenoma.
Identification of the type of thyrotoxic state has important
therapeutic implications. A multinodular goiter is
more resistant to therapy than Graves' disease and thus is
treated with higher doses of radioiodine (131I). A toxic adenoma
is treated with the maximum dose of 131I allowed in
an outpatient setting. The reason for using the maximum
dose is that the toxic portion of the gland receives most of
the therapeutic effect, and the suppressed portion of the
gland is left intact. As a result, treated patients often revert
to a euthyroid state after therapy.
Results of the thyroid study. This patient's study
is performed with 10 mCi of technetium-99m pertechnetate
and a low dose of 131I for uptake measurements.
A marker image, obtained to assess gland size, reveals
enlargement of the thyroid; the gland occupies more
area than expected between the chin and the sternal
notch (Figure 1). Three subsequent images—a highresolution
frontal planar image, a right anterior oblique
image, and a left anterior oblique image (Figure 2)—
together with the results of palpation confirm that the
gland is homogeneously enlarged. Iodine uptake is
elevated at 48%.
Given the homogeneous enlargement of this patient's
thyroid gland and the elevated iodine uptake, Graves'
disease is diagnosed.
After a negative result on a pregnancy test is obtained,
β-blocker therapy is started to help reduce cardiac
symptoms. The patient is subsequently treated
with 10 mCi of 131I.