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Nuclear medicine thyroid imaging
- 6. Fig. 2: Algorithm showing diagnostic approach to a patient with recurrent hyperthyroidism. sTSH = sensitive TSH. Parmar M S , Sturge C CMAJ 2003;169:415-417 ©2003 by Canadian Medical Association
- 10. The terminology stickler: 1. Thyrotoxicosis vs. hyperthyroid. 2. Toxic multinodular goiter vs Graves’ disease with nodules. 3. A cold or hot area is not necessarily a “nodule.” 4. Pinhole imaging is a form of planar imaging.
- 11. 1996 2003
- 13. I-123 THYROID April 30, 2010
- 14. Ant Post
Editor's Notes
- “Detective” theme: nuc. med. and lab tests to make dxs. Hinton, classic Graves. 52-y.o. with elevated thyroid hormone levels and low TSH. 24-h uptake is 87%. What is diagnosis? Based on what? Pyramidal lobe. Graves disease = diffuse toxic goiter. What about right upper pole on LAO? What are the markers and why? Any reservation about them? Why pinhole collimation? What can you say about the size of the gland? Palpation and ultrasound est mass= d1 x d2 x d3 x pi/6. What is collimation? (pinhole, but not “planar”.) What might you gain in some cases by using standard parallel hole collimation? Better marker accuracy, characterization of substernal goiter, possibly estimation of size. I had a case with everything the same except that the TSH was elevated. What do you think I reported? F/U, take home lesson. [Useful references are ATA guide and SNM guidelines.]
- Gorczyca, Elevated thyroid hormone levels and low TSH. Uptakes: 4 h 34%, 24 h 72%. What is diagnosis? What else might support the diagnosis. The patient had a normal thyroid stimulating immunoglobulln level. No pyramidal lobe. Palpation and correlation. Palpation revealed generalized enlargement. Don’t short-change palpation. Sometimes marking is beneficial with Co-57 or lead disk. (Tricky with pinhole.) Correlation with US? ???Spect CT. Treated with 15 mCi.
- Charles, Graves with cold nodules. Elevated thyroid hormone levels, low TSH. Uptake 58 at 4 h and 70 at 24 h. What is diagnosis and how can you tell. How can you further support it? In this case thyroid stimulating immunoglobulin is elevated. What else? US showed nodules, probably similar. No palpation reported.
- What do we see on this darker version of the RAO view. Wouldn’t expect to see pyramidal lobe; it would be suppressed. What is a pyramidal lobe? Should we now offer I-131 therapy to this patient? We recommended ultrasound with fine needle biopsy. Is this a toxic multinodular goiter? Graves’ disease patients can have cold nodules. How do we do thyroid scans (radiopharmaceutical)? I-123 vs pertechnetate. Tc can miss cold nodules. Organification. Salivary gland often seen on Tc but not I-123. Can’t do uptake with Tc. Some convenience to Tc. Can do uptake with e.g. small dose of I-131.
- Lizzarraga, prob. Thyroiditis. 56 y o female with complaints of nervousness and restlessness, tachycardia, heat intolerance, tremors, and weight loss. Elevated thyroid hormone levels and decreased TSH. Thyroid was tender. 24-h uptake was 1 %. What is diagnosis? Should we offer I-131 therapy? What are the dots at the top? What are our reasons for doing thyroid uptakes and scans in the presence of low TSH and high thyroid hormone? What if the uptake is 20%? What’s important diagnostically is whether or not it is very low. To distinguish true hyperthyroidism from other thyrotoxicosis such as this. Terminology: ATA: Thyrotoxicosis refers to a clinical state that results from inappropriately high thyroid hormone action in tissues generally due to inappropriately high tissue thyroid hormone levels. Hyperthyroidism is a form of thyrotoxicosis due to inappropriately high synthesis due to inappropriately high synthesis andsecretion of thyroid hormone(s) by the thyroid. This patient has thyrotoxicosis but not hyperthyroidism. What causes of thyrotoxicosis are there that aren’t hyperthyroidism? Several kinds of thyroiditis. How can you distinguish thyroiditis from factitious thyrotoxicosis? Serum thyroglobulin. Stool thyroid hormone levels have been reported. Also, rarely struma ovarii. Hyperthyroidism with iodine load could have low uptake. Remember that iodine can be a cause of hyperthyroidism. Otherwise, what is the use of a scan in thyrotoxicosis? Distinguish Graves from TNG or TA. With a known nodule, to see if it is cold. May discover a cold nodule that needs to be biopsied. Hot nodules are rarely cancer. Scan generally not needed unless TSH is low. Besides thyrotoxicosis: Evaluate substernal mass. Evaluate congenital hypothyroidism. Suppose I showed you this with the information that thyroid hormone levels were low. What if TSH was also low? Old-time intervention of TSH stimulation (bovine), to distinguish secondary hyperthyroidism. Obsolete. Detective story re causes of thyrotoxicosis, involving uptake, scan and lab values. Hamburger thyrotoxicosis. Female with clinical thyrotoxicosis, low TSH, low uptake (if we had done it), low T4, low free T4. Was taking T3.
- Fig. 2: Algorithm showing diagnostic approach to a patient with (recurrent) thyrotoxicosis. Martial arts thyroiditis (karate chop). Hamburger thyroiditis.
- Boxley, L lobectomy. 42-y o female referred because of concern about nodules (not because of thyrotoxicosis). Uptake was normal. Interpretation. She had had a left lobectomy because of a nodule. Could have had agenesis of left lobe.
- Koopman. Thyrotoxic. Uptakes 22 and 43%. What do you think about this and how would you next. No surgery. Agenesis Vs. Toxic nodule. How to distinguish between them? Palpation. Revealed right sided enlargement. Could this be Graves’ disease with a cold nodule and agenesis of the L lobe? Could do ultrasound, but no functional information.
- Koopman darker. Supports toxic nodule. How else could you prove a toxic nodule, based on the principle of healthy but suppressed left lobe tissue. Thallium or sestamibi. An intervention. Give TSH. Not utterly obsolete, but probably not much done.
- There is not total consistency about these. Even I, the certified stickler, will slip.
- 1996. Thyrotoxic patient. Diagnosis: toxic adenoma. (Toxic adenoma vs toxic multinodular goiter.) Treated with I-131 and returned for a scan in 2003. Comments? She was euthyroid. Still possible that this is an autonomous but not toxic nodule. How would you prove that? Give thyroid hormone and rescan? Is this the inevitable appearance of a followup scan? No. Patient could still have a clearcut autonomous or toxic nodule or a scar in place of the original nodule. Why do we care to distinguish among the kinds of hyper thyroidism? Prognostic: less chance of hypothyroidism. No concern about Graves’ ophthalmopathy. Needs a higher dose. Besides distinguishing between hyperthyroidism and other causes of thyrotoxicosis, what is the use of the uptake? Why 4 and 24 hour? Just for dose calculation. What are the risks of I-131 therapy? Hypothyroidism, radiation thyroiditis, even storm. Cancer? Maybe a worry with kids.
- Rudolph. Newborn baby with hypothyroidism. What is the diagnosis? Sublingual (ectopic) thyroid. What did we do the scan with? Note background. Important screening with free T4 and/or TSH. (Role of Pittsburgh.) Note that this diagnosis was missed on ultrasound. What are some causes and their appearance? What is the most common cause worldwide? Iodine deficiency. Even American pregnant women should be sure to get enough iodine. (?salt restriction). Ectopia Agenesis, e.g. hemiagenesis. Enzyme defect, e.g. organification. Secondary to pituitary failure. How will we know that? What are the points for using pertechnetate vs I-123? *I-123: reportedly more accurate, less trouble with saliva and salivary glands. Less effective dose than Tc. *Tc: :You can do it promptly. Mike says it is quicker scan. Mettler reports thyroids visualized in the case of organification defect only with Tc and not I. Why? He is talking about 24-h I-123 though. More dosimetry details. What’s the hurry to get it done? Even if you start thyroid hormone, the TSH stays up for a fair time. Possibly an issue of the iodine in T4, though. The important thing is to start thyroid hormone, so why do you want to know the etiology. Agenesis or ectopia means T4 for life. Other etiologies may warrant a trial off thyroid hormone at 3 y.o. There may be other reasons. The American Academy of Pediatrics guidelines call US and scanning “optional.”
- Referred patient as hyperthyroid with nodule. What do we do now? Palpate. 2nd nodule in isthmus found and confirmed by US and both bx’d. What to do if you palpate a nodule but the scan is normal, no hot, no cold. *marker to make sure it isn’t extrathyroidal *just biopsy *Do thyroid hormone suppression.
- Mitchell, wearing a cross.