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Iodine Induced Hyperthyroidism

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Posted: 10/1/2011 11:47:25 AM
 

Iodine Induced Hyperthyroidism by Jeffrey Dach MD

autonomous hot nodule iodine induced hyperthyroidism dr jeffrey dach mdIodine Induced Hyperthyroidism

by Jeffrey Dach MD

The Strange Case of the Autonomous Thyroid  Nodule

A young woman, Brenda,  was found to have essentially no urinary iodine excretion, indicating iodine deficiency. 

Although she had been in the US for twenty years, she was born and grew up in a foreign country noted for low iodine levels.

Because of iodine deficiency Brenda began a program of iodine supplementation with iodized salt.  About a week later, Brenda experienced an episode of severe tachycardia, with a sustained pulse rate of 220.  She was taken to the local hospital Emergency Room, where diagnostic testing was negative, and the doctors had no explanation for the tachycardia which resolved spontaneously shortly after arrival.  She was sent home with a Beta-Blocker Drug, Atenolol.

Above left image: Autonomous Thyroid Nodule on Radionuclide Thyroid scan (black arrow), also called a "Hot Nodule"  courtesy of wikimedia commons.

What Caused Brenda's Tachycardia ?  The Autonomous Nodule.

Brenda's tachycardia was a manifestation of hyperthyroidism from an autonomous thyoid nodule.  The increased iodine available to the nodule was immmediately and uncontrollably converted to thyroid hormone.  This is transient hyperthyroidism associated with an increase in dietary Iodine caused by autonomous thyroid nodule. 

An episode of hyperthyroidism after iodine ingestion is most commonly associated with an autonomous thyroid nodule that manufactures thyroid hormone independent of the normal control mechanism of TSH. 

The Sonogram and Radio-Nuclide Thyroid Scan

Brenda was advised to stop dietary Iodine and sent for diagnostic evaluation for an autonomous thyroid nodule, also called a  "hot nodule"Sure enough, Brenda's thyroid sonogram showed a thyroid nodule in the right upper lobe, and her Technesium 99M radionuclide scan showed that the nodule took up the tracer avidly, and was a "Hot Nodule", indicating an autonomous nodule. 

Thyroxine Suppression Test

In some cases, the nodule uptake may not be increased or "Hot" compared to the surrounding normal thyroid gland, and an additional step with a repeat scan after giving the patient Thyroxine (called a Thyroxine suppression test) may be needed to show increased uptake in the autonomous nodule.  The Thyroxine suppresses uptake in the normal thyroid gland, yet does not reduce the uptake in the autonomous hot nodule, allowing visibility on the uptake scan.

What is an Autonomous Nodule?

Recent medical research reveals that autonomous thyroid nodules are clones of cells that have a mutation in the TSH receptor (Thyroid Stimulating Hormone Receptor). (9)  These mutations usually arise as a result of iodine deficiency in patients who spend their childhood in iodine deficient regions.  The mutations make these nodules independent of TSH control usually found in normal thyroid tissue.  The nodules make thyroid hormone uncontrollably based on the availability of Iodine.

Even small amounts of iodine supplements normally found in Iodized Salt can cause transient hyperthyroidism in patients with autonomous nodules.(1-7)  This increased prevalence of hyperthyroidism was reported with the introduction of Iodized Salt and Iodized Bread programs to prevent iodine deficiency in various countries including the US.  In addition, iodinated radiographic contrast (such as used for a CAT scan) can also cause transient hyperthyroidism in susceptible patients with autonomous nodules.

Treatment of Autonomous Nodule

If hyperthyroidism becomes clinically apparent and requires treatment, an elegant method is percutaneous ethanol injection into the nodule under ultrasound control.(38-40)   Other mainstream treatments include surgical removal and radioactive iodine ablation.

Another way to check Iodine Sufficiency- Serum Thyroglobulin

Serum thyroglobulin is also useful in evaluating Iodine status.

The Autonomous Nodule Originates in an Iodine Deficient Region

Luckily, autonomous nodules are quite rare in the US after iodine supplementation  to table salt in 1924.  However, when people migrate to the United States after growing up in an iodine deficient region, these people may harbor autonomous nodules and may present with features of transient hyperthyroidism when supplemented with iodine in the diet.  Iodine deficiency is a risk factor for mutations in the TSH receptors and development of the autonomous thyroid nodule. 

Articles With Related Interest

Iodine is Safe and Effective

Iodine Treats Breast Cancer, Overwhelming Evidence

Iodine and Breast Cancer Prevention

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Posted: 10/1/2011 12:35:15 PM
 
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joecool55

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Posted: 10/1/2011 2:47:42 PM
 
What does someone do with iodine if they discover that they have an autonomous nodule? They wouldn't want to induce hyperthyroidism by taking iodine, but they also wouldn't want to stay iodine deficient. What is the best solution?
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