|Year : 2018 | Volume
| Issue : 4 | Page : 140-142
Brief overview of the role of nuclear medicine in evaluation of hyperthyroidism
Department of Nuclear Medicine, Christian Medical College, Vellore, Tamil Nadu, India
|Date of Web Publication||16-Apr-2019|
Department of Nuclear Medicine, Christian Medical College, Vellore, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Excessive production of thyroid hormones from the thyroid gland leads to hyperthyroidism. The role of radioiodine uptake study has been well established in the evaluation of hyperthyroidism. This article aims to delineate the nuances involved in the diagnosis and treatment of hyperthyroidism using radioiodine.
Keywords: Hyperthyroidism, radioiodine thyroid uptake test, thyroid hormones
|How to cite this article:|
Mathew D. Brief overview of the role of nuclear medicine in evaluation of hyperthyroidism. Curr Med Issues 2018;16:140-2
| Introduction|| |
Hyperthyroidism is a condition which is the result of the thyroid gland producing abnormal amount of thyroid hormones. It results in increasing metabolism significantly, causing significant weight loss, tachycardia, arrhythmia, increased sweating, and irritability.
| Symptoms and Signs|| |
Patient complaints of weight loss, increased appetite, palpitations, nervousness and irritability, tremors, sweating, menstrual irregularities, heat intolerance, diarrhea, swelling of the gland, increased tiredness and muscle weakness, disturbed sleep, and other nonspecific complaints rarely. It can be asymptomatic and incidentally picked up.
Careful examination may elicit hyperreflexia, warm, moist skin tachycardia, and arrhythmia.
Graves' ophthalmopathy is protrusion of the eyeballs resulting in incomplete closure of the eyelids with associated exposure keratitis. This condition can present to the eye doctor with redness of the eye, with irritation and tearing and visual disturbances.
| Mechanism|| |
T4 and T3 are released from thyroid gland under the control of pituitary gland through thyroid-stimulating hormone (TSH) through the negative feedback mechanism based on the level of T4 and T3 in the blood. This balance is altered in hyperthyroidism.
| Complications|| |
- Atrial fibrillation and congestive heart failure
- Graves' ophthalmopathy
- Graves' dermopathy is redness and thickening of the skin seen usually in the lower limbs
- Thyrotoxic crisis.
| Case|| |
A 30-year-old working female, who was recently divorced, started to smoke to stay awake to work extra hours to get more money as over time. She noticed that she was more anxious and irritable than usual and attributed it to the extra hours and stress that she was currently undergoing. Over a period of few months, she found weight loss despite eating more than the usual amount and palpitations. When she presented to the physician, she was found to have warm moist skin with tachycardia. Reflexes were found to be exaggerated.
The physician evaluated and gave her blood tests including the thyroid function tests. It was found that she had increased thyroid hormones with suppressed TSH values and a diagnosis of hyperthyroidism was made. This was confirmed with increased uptake in thyroid uptake study.
Blood tests and their normal ranges are as follows:
- Total T3 (TT3) serum: 90–190 ng/dL
- Total thyroxine (TT4) serum: 4.5–12.5 μg/dL
- TSH serum: 0.3–4.5 μIU/ml
- Free thyroxine (FT4): 0.8–2.0 ng/dL.
Radioiodine thyroid uptake test
This test is done to check the percentage of iodine uptake to the dose given.
The patient is asked to orally take in iodine radioisotope (liquid or capsule form) and this is absorbed from the gut through the bloodstream and preferentially taken up by the thyroid gland. This uptake is measured with gamma rays captured by a probe. The dose usually given is 1 MBq.
Following oral administration of iodine-131, thyroid uptake values were calculated after background correction at 2, 6, and 24 h. Images of the thyroid gland were acquired after 24 h in the anterior view.
The normal uptake values can be interfered with intake of iodine-containing foods – milk products and seafood. Other factors to be considered are recent use of iodinated contrast in recent computed tomography scans (within 3 months) or gastroenteritis.
The two iodine radioisotopes used are 123-I and 131-I. 123-I has a shorter half-life than 131-I with lesser radiation and shorter time period for the scan.
Pregnancy and lactation.
The radiation dose is too small to harm the patient. Inadvertent use in lactating mothers can potentially cause damage to the thyroid gland of the child and can be of risk of teratogenicity in case of pregnancy.
The radioactive iodine (RAI) is cleared from the body through urine. The patient is asked to take in water and make sure that after the urine is passed; flushing is done to prevent any contamination with other members using the same.
Thyroid uptake study is approximately costing Rupees 2000/-.
Normal uptake values (range [%])
- 2 h: Normal 8%–17%
- 6 h: Normal 13%–25%
- 24 h: Normal 23%–40%.
Causes of thyrotoxicosis
The common causes of thyrotoxicosis are as follows –
- Thyrotoxicosis associated with a normal or elevated RAI uptake over the neck
- Graves' Disease
- Toxic adenoma
- Toxic multinodular goiter
- Trophoblastic disease
- TSH-producing pituitary adenomas
- Resistance to thyroid hormone.
- Thyrotoxicosis associated with a near-absent RAI uptake over the neck
- Painless (silent) thyroiditis
- Amiodarone-induced thyroiditis
- Subacute (granulomatous and De Quervain's) thyroiditis
- Palpation thyroiditis
- Iatrogenic thyrotoxicosis
- Factitious ingestion of thyroid hormone
- Struma ovary
- Acute thyroiditis
- Extensive metastases from follicular thyroid cancer.
The thyroid uptake study images from a normal patient, a patient with toxic adenoma, a patient with Graves' disease and a patient with thyroiditis are shown in [Figure 1], [Figure 2], [Figure 3], [Figure 4], respectively.
|Figure 1: Normal thyroid gland. A 35-year-old female who was evaluated for tachycardia was found to have thyroid uptake values as 11%/23%/36% – Euthyroid status. (Image courtesy: Nuclear Medicine CMC Vellore); SSN – Suprasternal notch.|
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|Figure 2: Toxic adenoma. A 50-year-old female with complaints of the right neck swelling and recent tremors was found to have thyroid uptake values as 42%/60%/78% – Hyperthyroidism. (Image courtesy: Nuclear Medicine CMC Vellore); SSN – Suprasternal notch.|
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|Figure 3: Graves' disease. A 25-year-old female with complaints of significant loss of weight was found to have thyroid uptake values as 47%/67%/79% – Hyperthyroidism. (Image courtesy: Nuclear Medicine CMC Vellore); SSN – Suprasternal notch.|
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|Figure 4: Thyroiditis. A 65-year-old female with complaints of palpitations was found to have thyroid uptake values as 2%/3%/2% suggesting thyroiditis. (Image courtesy: Nuclear Medicine CMC Vellore); SSN – Suprasternal notch.|
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Images of the thyroid gland in thyroid uptake study
The patient described above was diagnosed to have Graves' disease and was treated with radioiodine 5 mCi orally along with beta blockers. She had symptomatic improvement and was monitoring her thyroid function tests three monthly. After a period of 1 year, she became hypothyroid which was then supplemented by a small dose of thyroid hormones.
The various modalities used for the treatment of hyperthyroidism include –
- RAI – Usually, a mean dose of 10–15 mCi (370–555 MBq) is administered orally (5 mCi in our center) causing radioactive damage to the cells in the thyroid gland with resultant remission within 3 to 6 months
- Antithyroid drugs – Prevents excess production of thyroid hormones causing symptomatic improvement in 6 to 12 weeks
- Beta-blockers – Reduces the symptoms of tachycardia and palpitations
- Surgery – Total thyroidectomy is offered if any of the above treatments could not be offered due to other reasons.
After and during this treatment, thyroid function tests should be monitored every 3 months to check for hypothyroidism and as needed to start thyroid supplements appropriately.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]