Hyperthyroid Disorders

Lesson 6: Conventional Treatment Options

Radioiodine

Radioiodine is still the most popular treatment for hyperthyroidism in the United States. However, as more patients become involved in their healthcare and more information about the hazards of radioiodine has become available in the last few years, more patients are opting for ATDs or surgery.

RAI Safety
According to Dr. John Gofman, the country’s leading radiation expert, there is no safe medical use for radioiodine. Radioiodine either mutates or destroys the cells at its path length. The actions of RAI persist for months to years. While the half-life of I-131, the isotope most often used, is only a few days, radioiodine persists for a long time as its being broken down. A November 2004 press release cautioned that patients having radioiodine ablation will set off airport radiation detectors for an average of 90 days.

Although patients in the U.S. wishing to become pregnant after RAI are advised to wait 6 months to 1 year, in most other parts of the world, RAI is prohibited for women of childbearing age. There are no long-term studies available of the children born to irradiated women. However, data released from the radioiodine spill in Chernobyl shows an increased rate of thyroid and other cancers in people exposed to RAI. Radiation is emitted for many months after RAI ablation.

RAI Procedure
Prior to this procedure, patients are asked to sign a waiver or consent, stating that they have been advised of other treatment options and they are instructed to avoid intimate contact and direct contact with children for at least 8 days. Patients are also instructed to flush the toilet twice after using it and to dispose of all dishes and utensils that are used. In most states the consent advises that the risk for thyroid eye disease is increased. It’s important to read the consent and ask questions ahead of time. Once RAI is administered there is no way to change the outcome.

For ablation, which refers to destruction of the thyroid gland, an oral dose of I-131 is administered. There is no agreement on an ideal dose. Over the years the philosophy on dosage has changed. At one time, lower doses were used in an attempt to prevent hypothyroidism. However, lower doses are more likely to cause mutations, and mutated cells can be passed on to progeny and over time lead to cancer. Today, higher doses are usually used to prevent the possibility of developing malignancies. The usual dose delivers 5,000-10,00 rads to thyroid tissue and other tissue that concentrates iodine. This includes the stomach, breast, pancreas, salivary glands, pituitary gland and other tissues.

Adverse Effects
Radiation thyroiditis occurs within the first days to weeks after treatment. This can cause neck pain, sore throat, painful salivary glands, nausea and vomiting. It can also cause an exacerbation or worsening of hyperthyroid symptoms, which can progress to thyroid storm. Most patients who develop thyroid storm due so within the first 8 weeks after ablation. Because thyroid hormone and thyroid antibodies are released from dying thyroid cells, thyroid hormone levels can rise for up to 8 weeks or longer.

In patients with mild hyperthyroidism, thyroid cell destruction may be sufficient to cause a rapid move into hypothyroidism. For these reasons it’s important for patients to be aware that hyperthyroidism can worsen and hypothyroidism can develop quickly. Many patients are told to return to their doctors at four weeks. Studies show that mortality from thyroid storm is most likely from 3-5 weeks after RAI. Patients should be aware of symptoms of both hypothyroidism and thyroid storm and notify their doctor as needed so that they can have their levels checked or be examined.

In most cases, hypothyroidism develops within the first week to first 3 months after RAI. By the first year after RAI, up to 90 percent of irradiated patients become hypothyroid. However, it’s not unusual for doctors to order a second or third ablation before the first year is up, not realizing that the effects persist. These patients are at a higher risk for TED and other adverse effects of radiation.

Over time, hypothyroidism worsens. The average dose of replacement hormone needed one year after RAI is 0.1 mg levothyroxine. At 6 years the average dose is 0.175. With decreased thyroid function, many patients are unable to convert T4 into T3 and over time require T3 as well as T4 supplementation. For this reason it’s important that both FT4 and FT3 levels are checked. TSH is frequently falsely elevated because of the dramatic increase in TSH receptor antibodies, which can persist for many years after RAI.

RAI is known to increase or precipitate the development of thyroid eye disease, pretibial myxedema and acropachy. These conditions, which are further explored in chapter 8, are known to develop up to 30 years after RAI. Over time, acropachy can lead to elephantiasis. RAI is also known to damage the other glands that absorb iodine, including salivary glands and the pancreas. These organs may have mild to markedly diminished functioning. Because of diminished salivary gland function, irradiated patients are more likely to experience dental problems, and because of the immune system assault and stimulation, irradiated patients are more likely to develop other autoimmune diseases.

Advantages
The major advantage of RAI is its low cost. Most patients become hypothyroid within a short time, and they can be treated with ATDs until hypothyroidism develops. While the symptoms of hypothyroidism can be far worse than those of hyperthyroidism, they are not considered as important despite the fact that myxedema coma has a much higher mortality rate than thyroid storm.

Because hypothyroidism is not considered important, patients are advised to only have yearly checkups. Replacement hormone is also very cheap and most patients are monitored with an annual TSH level. For patients in rural areas that have difficulty getting to appointments or patients who have other time constraints, RAI can be a good short-term choice. The long-term effects, however, are still being debated.

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