Current Medical Issues

REVIEW ARTICLE
Year
: 2018  |  Volume : 16  |  Issue : 4  |  Page : 140--142

Brief overview of the role of nuclear medicine in evaluation of hyperthyroidism


David Mathew 
 Department of Nuclear Medicine, Christian Medical College, Vellore, Tamil Nadu, India

Correspondence Address:
David Mathew
Department of Nuclear Medicine, Christian Medical College, Vellore, Tamil Nadu
India

Abstract

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.



How to cite this article:
Mathew D. Brief overview of the role of nuclear medicine in evaluation of hyperthyroidism.Curr Med Issues 2018;16:140-142


How to cite this URL:
Mathew D. Brief overview of the role of nuclear medicine in evaluation of hyperthyroidism. Curr Med Issues [serial online] 2018 [cited 2019 Nov 17 ];16:140-142
Available from: http://www.cmijournal.org/text.asp?2018/16/4/140/256316


Full Text

 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.[1] 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 failureOsteoporosisGraves' ophthalmopathyGraves' dermopathy is redness and thickening of the skin seen usually in the lower limbsThyrotoxic 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.

Diagnosis

Blood tests and their normal ranges are as follows:

Total T3 (TT3) serum: 90–190 ng/dLTotal thyroxine (TT4) serum: 4.5–12.5 μg/dLTSH serum: 0.3–4.5 μIU/mlFree 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.

Procedure

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.

Interference

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.

Radioisotopes

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.

Contraindications

Pregnancy and lactation.

Complications

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.[2]

Elimination

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.

Cost

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 –[3]

Thyrotoxicosis associated with a normal or elevated RAI uptake over the neck

Graves' DiseaseToxic adenomaToxic multinodular goiterTrophoblastic diseaseTSH-producing pituitary adenomasResistance to thyroid hormone.

Thyrotoxicosis associated with a near-absent RAI uptake over the neck

Painless (silent) thyroiditisAmiodarone-induced thyroiditisSubacute (granulomatous and De Quervain's) thyroiditisPalpation thyroiditisIatrogenic thyrotoxicosisFactitious ingestion of thyroid hormoneStruma ovaryAcute thyroiditisExtensive 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}{Figure 2}{Figure 3}{Figure 4}

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.

Treatment

The various modalities used for the treatment of hyperthyroidism include –[4]

RAI[5] – 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 monthsAntithyroid drugs – Prevents excess production of thyroid hormones causing symptomatic improvement in 6 to 12 weeksBeta-blockers – Reduces the symptoms of tachycardia and palpitationsSurgery – Total thyroidectomy is offered if any of the above treatments could not be offered due to other reasons.

Follow-up

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

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1Léger J, Carel JC. Diagnosis and management of hyperthyroidism from prenatal life to adolescence. Best Pract Res Clin Endocrinol Metab 2018;32:373-86.
2Nguyen CT, Sasso EB, Barton L, Mestman JH. Graves' hyperthyroidism in pregnancy: A clinical review. Clin Diabetes Endocrinol 2018;4:4.
3Ross DS, Burch HB, Cooper DS, Greenlee MC, Laurberg P, Maia AL, et al. 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis. Thyroid 2016;26:1343-421.
4Kahaly GJ, Bartalena L, Hegedüs L, Leenhardt L, Poppe K, Pearce SH. 2018 European Thyroid Association guideline for the management of Graves' hyperthyroidism. Eur Thyroid J 2018;7:167-86.
5Rokni H, Sadeghi R, Moossavi Z, Treglia G, Zakavi SR. Efficacy of different protocols of radioiodine therapy for treatment of toxic nodular goiter: Systematic review and meta-analysis of the literature. Int J Endocrinol Metab 2014;12:e14424.