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Scintigraphic Manifestations of Thyrotoxicosis¹

¹ From the Departments of Radiology (C.M.I., S.M.K.) and Medicine (A.E.D., S.J., J.L.M., D.M.C.), Thomas Jefferson University Hospital, 132 S 10th St, 861 Main Bldg, Philadelphia, PA 19107. Received August 30, 2002; revision requested November 26; final revision received March 13, 2003; accepted March 17. Address correspondence to C.M.I. (e-mail: charles.intenzo@jefferson.edu).

View larger version (158K): [in a new window]   Figure 1.  Graves disease in a 24-year-old woman. Laboratory values were as follows: T4 = 16.7 µg/dL, T3 = 311 ng/dL, and TSH < 0.01 µIU/mL. The 24-hour RAIU was 84%. Anterior distant image obtained with Tc-99m pertechnetate shows an enlarged thyroid. The target-to-background activity is increased to such an extent that the submandibular salivary glands (arrowhead) are barely visualized. Note the appearance of the pyramidal lobe (large arrow). The round photopenic area (small arrow) in this and subsequent figures represents the 2-cm lead marker placed at the suprasternal notch.

View larger version (158K): [in a new window]   Figure 2.  Marine-Lenhart syndrome in a 52-year-old woman. Laboratory values were as follows: free T4 = 2.9 ng/dL, T3 = 181 ng/dL, and TSH < 0.01 µIU/mL. Anterior Tc-99m pertechnetate image shows an enlarged thyroid with diffusely increased radiotracer trapping, as in Graves disease per se. However, within the gland are distinct cold nodules (arrows).

View larger version (129K): [in a new window]   Figure 3.  Toxic autonomous nodule in a 49-year-old woman. Laboratory values were as follows: T4 = 15.1 µg/dL, T3 = 304 ng/dL, and TSH < 0.01 µIU/mL. The 24-hour RAIU was elevated (46%). Anterior distant Tc-99m pertechnetate image shows a hot nodule that occupies most or all of the right thyroid lobe (large straight arrow) with near-total suppression of the left lobe (small straight arrow). The background activity is diminished to such an extent that the salivary glands (curved arrows) are barely visualized. Arrowhead = 2-cm lead marker.

View larger version (143K): [in a new window]   Figure 4.  Toxic multinodular goiter in a 71-year-old man with anxiety and weight loss. Laboratory values were as follows: T4 = 12.1 µg/dL, T3 = 299 ng/dL, and TSH < 0.01 µIU/mL. The RAIU was 17% at 6 hours and 37% at 24 hours. Anterior close-up I-123 image shows an enlarged thyroid with overall nonuniform uptake. Areas of both increased and decreased activity are scattered throughout the gland; the increased uptake represents hot nodules, whereas the decreased uptake represents a combination of suppressed extranodular tissue and cold thyroid nodules.

View larger version (195K): [in a new window]   Figure 5.  Subacute thyroiditis in a 32-year-old woman with relatively rapid onset of palpitations, insomnia, anxiety, neck pain, and mood swings, all of which were preceded by an upper respiratory tract infection. Physical examination demonstrated neck tenderness. Laboratory values were as follows: free T4 = 2.5 ng/dL, free T3 = 640 ng/L, and TSH < 0.01 µIU/mL. The 24-hour RAIU was 0.5%. Anterior distant Tc-99m pertechnetate image shows minimal thyroid activity (arrow) only slightly higher than background activity.

View larger version (208K): [in a new window]   Figure 6.  Silent thyroiditis in a thyrotoxic 28-year-old woman. Laboratory values were as follows: T4 = 21 µg/dL, T3 = 289 ng/dL, and TSH < 0.02 µIU/mL. The 24-hour RAIU was 0.6%. Anterior distant Tc-99m pertechnetate image shows a barely visible thyroid (thick arrow). The dark structures (thin arrow) are the salivary glands, which are very prominent due to the low thyroid-to-background activity. The round photopenic area (medium-sized arrow) is the 2-cm lead marker placed at the suprasternal notch. Owing to slight thyromegaly and the patient’s morbid fear of thyroid cancer (as diagnosed in a sibling), a large-core needle biopsy was performed, which demonstrated lymphocytic infiltrations within the thyroid parenchyma. (Reprinted, with permission, from reference 34.)

View larger version (166K): [in a new window]   Figure 7.  Silent thyroiditis during the recovery phase in a 55-year-old woman with intermittent episodes of anxiety, palpitations, and irritability. Laboratory values were as follows: free T4 = 1.9 ng/dL, total T3 = 265 ng/dL, and TSH = 0.1 µIU/mL. Physical examination revealed a pulse rate of 68 beats per minute (during ß-blockade), and there was no hand tremor. On palpation of the neck, there was no goiter, no palpable nodules, and no tenderness. One week after thyroid function testing, the 24-hour RAIU was 37%. Tc-99m pertechnetate image obtained at this time shows a normal-sized gland with increased thyroid-to-background activity. On thorough requestioning, the patient thought that her symptomatic episodes had become slightly less frequent over time (although this conclusion was not entirely reliable due to the ß-blockade). The differential diagnosis was Graves disease with both a normal-sized gland and relatively rapid iodine turnover versus a healing or recovery phase of silent thyroiditis. Since the probability of the former was intuitively less likely than that of the latter, the presumptive diagnosis was silent thyroiditis in recovery. We recommended to the patient that any treatment for Graves disease be deferred pending repeated thyroid function testing 4-6 weeks later to definitely exclude the possibility of Graves disease. The results of her thyroid function tests eventually normalized.

View larger version (181K): [in a new window]   Figure 8.  Iodine-induced hyperthyroidism in a 68-year-old man. His history was significant for amiodarone therapy for intractable atrial fibrillation. Laboratory values were as follows: free T4 = 1.7 ng/dL, T3 = 351 ng/dL, and TSH = 0.05 µIU/mL. The 24-hour RAIU was 2.7%. Anterior distant Tc-99m pertechnetate image shows decreased radiotracer trapping throughout the thyroid.

View larger version (186K): [in a new window]   Figure 9.  Factitious hyperthyroidism in a 72-year-old male physician who was admitted to the hospital with multiple premature ventricular contractions. The work-up included thyroid function testing, which demonstrated the following values: free T4 = 5.5 ng/dL, T3 = 150 ng/dL, and TSH < 0.01 µIU/mL. The I-123 RAIU at 24 hours was low (2%). Anterior distant I-123 image shows decreased activity throughout the thyroid. The possibility of iodine-induced hyperthyroidism was not considered because there was no known previous iodine administration. The initial presumptive diagnosis was silent thyroiditis. However, the consulting endocrinologist measured the serum thyroglobulin level, which was undetectable; this result essentially confirmed the diagnosis of factitious hyperthyroidism. When confronted with this information, the patient admitted he was secretly taking L-thyroxine (a T4 preparation) to "enhance sexual potency."

View larger version (143K): [in a new window]   Figure 10a.  Thyrotoxicosis from metastatic thyroid cancer in a 53-year-old man with a mass compressing the lower thoracic spinal cord and a history of subtotal thyroidectomy for follicular thyroid cancer 5 years earlier (at another institution). Biopsy of the mass revealed metastatic follicular thyroid cancer. Iatrogenic hyperthyroidism from overzealous thyroid suppression with L-thyroxine was the presumptive diagnosis. In preparation for I-131 ablation, L-thyroxine therapy was stopped for 5 weeks. However, the thyrotoxic symptoms persisted; the free T4 level was 2.6 ng/dL, the free T3 level was 752 ng/L, and the TSH level was 0.02 µIU/mL. Computed tomography (CT) of the chest showed a destructive mass in the right chest wall. The diagnosis of thyrotoxicosis caused by metastatic follicular thyroid cancer was made. I-131 ablation was then considered. Thallium-201 whole-body scanning was performed immediately before I-131 ablation. We eliminated the diagnostic I-131 study to save time (scanning is performed 48 hours after administration of the diagnostic dose of I-131) and to avoid the possibility of stunning by the diagnostic dose. (a) Anterior Tl-201 whole-body image shows metastases in the right chest wall (arrowhead) and thoracic spine (arrow). (b) Anterior (left) and posterior (right) postablation I-131 images obtained 1 week after administration of 200 mCi (7,400 MBq) of I-131 show thyroid bed uptake (curved arrow), a right infraclavicular lymph node (small straight arrow), the chest wall metastasis (arrowheads), and the thoracic spine lesion (large straight arrow).

View larger version (108K): [in a new window]   Figure 10b.  Thyrotoxicosis from metastatic thyroid cancer in a 53-year-old man with a mass compressing the lower thoracic spinal cord and a history of subtotal thyroidectomy for follicular thyroid cancer 5 years earlier (at another institution). Biopsy of the mass revealed metastatic follicular thyroid cancer. Iatrogenic hyperthyroidism from overzealous thyroid suppression with L-thyroxine was the presumptive diagnosis. In preparation for I-131 ablation, L-thyroxine therapy was stopped for 5 weeks. However, the thyrotoxic symptoms persisted; the free T4 level was 2.6 ng/dL, the free T3 level was 752 ng/L, and the TSH level was 0.02 µIU/mL. Computed tomography (CT) of the chest showed a destructive mass in the right chest wall. The diagnosis of thyrotoxicosis caused by metastatic follicular thyroid cancer was made. I-131 ablation was then considered. Thallium-201 whole-body scanning was performed immediately before I-131 ablation. We eliminated the diagnostic I-131 study to save time (scanning is performed 48 hours after administration of the diagnostic dose of I-131) and to avoid the possibility of stunning by the diagnostic dose. (a) Anterior Tl-201 whole-body image shows metastases in the right chest wall (arrowhead) and thoracic spine (arrow). (b) Anterior (left) and posterior (right) postablation I-131 images obtained 1 week after administration of 200 mCi (7,400 MBq) of I-131 show thyroid bed uptake (curved arrow), a right infraclavicular lymph node (small straight arrow), the chest wall metastasis (arrowheads), and the thoracic spine lesion (large straight arrow).

View larger version (157K): [in a new window]   Figure 11a.  Struma ovarii in an 81-year-old woman with thyrotoxicosis, ascites, and a pelvic mass. Laboratory values were as follows: T4 = 13.7 µg/dL, T3 = 200 ng/dL, and TSH < 0.01 µIU/mL. The initial imaging study was pelvic CT. (a) CT scan shows a left ovarian mass (arrow). (b) Top left: Anterior distant Tc-99m pertechnetate image shows decreased tracer activity in a small thyroid (arrow). The 24-hour RAIU was 3%. Because of the known pelvic mass, imaging of the pelvis was also performed. Top right: Anterior image shows the pelvic mass (arrowhead) displacing the bladder to the right (arrow). To optimally image the pelvic mass without the background activity that appears with Tc-99m pertechnetate, scanning was repeated with I-123. Bottom left: I-123 image obtained after voiding shows the mass (arrow). At surgery, the entire left ovary was removed, revealing a large struma ovarii containing thyroid tissue, which stained positive for thyroglobulin. Thyroid function soon returned to normal. Two months later, the 24-hour RAIU was 16%; Tc-99m pertechnetate scanning was performed. Bottom right: Anterior close-up Tc-99m pertechnetate image of the thyroid shows normal tracer concentration. Ectopic thyroid tissue within the pelvis is better visualized with I-123 than with pertechnetate, since the bladder is visible with the latter. Conceivably, this visibility could result in the bladder obscuring the ectopic thyroid tissue or erroneously being interpreted as representing the thyroid tissue.

View larger version (148K): [in a new window]   Figure 11b.  Struma ovarii in an 81-year-old woman with thyrotoxicosis, ascites, and a pelvic mass. Laboratory values were as follows: T4 = 13.7 µg/dL, T3 = 200 ng/dL, and TSH < 0.01 µIU/mL. The initial imaging study was pelvic CT. (a) CT scan shows a left ovarian mass (arrow). (b) Top left: Anterior distant Tc-99m pertechnetate image shows decreased tracer activity in a small thyroid (arrow). The 24-hour RAIU was 3%. Because of the known pelvic mass, imaging of the pelvis was also performed. Top right: Anterior image shows the pelvic mass (arrowhead) displacing the bladder to the right (arrow). To optimally image the pelvic mass without the background activity that appears with Tc-99m pertechnetate, scanning was repeated with I-123. Bottom left: I-123 image obtained after voiding shows the mass (arrow). At surgery, the entire left ovary was removed, revealing a large struma ovarii containing thyroid tissue, which stained positive for thyroglobulin. Thyroid function soon returned to normal. Two months later, the 24-hour RAIU was 16%; Tc-99m pertechnetate scanning was performed. Bottom right: Anterior close-up Tc-99m pertechnetate image of the thyroid shows normal tracer concentration. Ectopic thyroid tissue within the pelvis is better visualized with I-123 than with pertechnetate, since the bladder is visible with the latter. Conceivably, this visibility could result in the bladder obscuring the ectopic thyroid tissue or erroneously being interpreted as representing the thyroid tissue.

View larger version (180K): [in a new window]   Figure 12.  TSH-induced thyrotoxicosis in a 33-year-old woman. Laboratory values were as follows: free T4 = 2.0 ng/dL, T3 = 191 ng/dL, and TSH = 37.1 µIU/mL. The latter measurement was repeated, and the value was 39.0 µIU/mL. Anterior distant Tc-99m pertechnetate image shows relatively high target-to-background activity, similar to that seen in Graves disease. CT of the brain performed at an outside imaging center revealed a pituitary tumor. Upon removal of the tumor, the symptoms subsided and thyroid function returned to normal.