lunedì 25 agosto 2008
0.1 mCi of I-123 in the form of sodium iodide capsule was administered orally. 4 and 24 hour radioiodine uptakes were determined. The following day, 5.4 mCi of Tc 99m sodium pertechnetate was injected intravenously for the perfusion part of the scan followed by routine planar and pinhole imaging of the neck.
There is increased flow to the thyroid gland bilaterally. Planar and pinhole imaging of the neck demonstrate a symmetrically enlarged gland with homogenous radiotracer uptake. Thyroid to salivary gland ratio is increased and there is suppression of the background. Four-hour radioactive iodine uptake (RAIU) is 22.2% and 24-hour radioactive iodine uptake is 55.3%.
Diagnosis: Graves disease
Graves disease is the most common etiology of thyrotoxicosis and predominantly occurs in middle-age females. Binding of immunoglobulins to TSH receptors results in autonomous, inappropriate hyperfunctioning of the thyroid gland. This result in suppression of TSH levels, which are typically less than 0.01 mU/L.
Thyroid scintigraphy and RAIU determination are useful for distinguishing Graves disease from other causes of thyrotoxicosis in ambiguous cases. Thyroid scan radiotracers include Tc99m pertechnetate, I123 and I131. I123 is preferred over I131 for most applications due to the shorter half-life and lower peak energy of the I123 gamma photon, which results in more optimal image quality and lower radiation dose to the patient. Imaging is performed 2-6 hours after I123 is administered. Radioiodine distributes to the salivary glands, stomach and choroid plexus and is only stored within the thyroid. The classic thyroid scan findings associated with Graves disease include homogeneously increased activity in an enlarged thyroid gland, increased thyroid to salivary gland activity and suppression of the background. RAIU measurements can be performed at 4-6 hours and 24 hours. Graves disease usually yields RAIU values of 40 to 80% (normal 10 to 30%) at 24 hours. However, high-turn over varieties may manifest only as elevated 4-6 hour RAIU values (normal 4 to 15%), as 24 hour RAIU results may be normal or only mildly elevated.
Patients with Graves disease are initially treated with beta-blockers and temporarily with thyroid specific medications, such as PTU and methimazole. Radioiodine therapy, rather than surgery, represents the definitive treatment of choice. Indeed, high cure rates result from I131 treatment doses of at least 15 mCi. Side-effects for Graves treatment doses include hypothyroidism, radiation induced thyroiditis, xerostomia, sialadenitis, change in taste, and worsening of ophthalmopathy. Leukemia and other secondary malignancies are rare in any setting and not relevant to the Graves/hyperthyroid treatment doses