A new article published in StatPearls discussed that iodine is an essential micronutrient that has a crucial role in metabolism. It is oxidized to produce iodine-containing thyroid hormones. Thyroid hormones, on the other hand, are necessary for controlling growth, metabolism and many other body functions. They are crucial for fetal and neonatal brain development.

The authors stated that iodine deficiency has long been a recognized global problem and remains a leading cause of preventable fetal brain damage. Iodine deficiency in pregnancy leads to hypothyroidism and impaired infant neurobehavioral development.

Iodine is not synthesized in the human body and must be obtained from food, dietary supplements, medications, and iodinated contrast media. The recommended dietary allowance (RDA) for adults is 150 micrograms/day; 220 to 250 micrograms/day for pregnant women; and 250 to 290 micrograms/day during breastfeeding. Generally, up to 1 mg/day is safe for most individuals. Sources of excess iodine can be from overconsumption of iodized salt, drinking water, milk rich in iodine, certain seaweeds and dietary supplements containing iodine. Ingestion of over 1.1 mg/day of iodine may be harmful and can lead to acute and/or chronic toxicity.

Iodine excess can cause subclinical or overt thyroid dysfunction in patients with specific risk factors, including those with pre-existing thyroid disease, the elderly, fetuses and neonates. The effects of excess iodine are variable among individuals and relate to the individual’s underlying thyroid function. Iodine toxicity may lead to thyroiditis, hypothyroidism, hyperthyroidism and thyroid papillary cancer. Clinical features of iodine toxicity from oral ingestion can range from mild to severe. Mild symptoms manifest as GI upset, nausea, vomiting and diarrhea, which may progress to delirium, stupor and shock – rarely fatal.

Iodine toxicity most commonly results from over-consumption of dietary supplements. Foods containing iodine include iodized salt (one gram contains about 77ug of iodine), drinking water, milk, certain seafood and seaweeds. Some oral medications may also contain iodine, such as amiodarone and potassium supplements. Tincture of iodine and betadine are topical medications used as antiseptics and can cause a rash or blistering when applied topically, and more severe toxicity if accidentally ingested.

Treatment/Management

Approach to management of iodine toxicity entails supporting the airway, breathing and circulation. If the patient is unstable, they should immediately be placed on a cardiac monitor with supplemental oxygen, with two large-bore IVs placed. Endotracheal intubation is necessary if the patient is unable to protect their airway due to an altered mental status.

There is no specific antidote to iodine poisoning. If the patient is stable, alert and protecting their airway, activated charcoal should be given to decontaminate the gastrointestinal tract. Hospitalization or prolonged observation in the emergency department may be necessary until deemed medically stable.

Complications

Scientists hypothesize that the increased incidence of thyroid cancer may be associated with iodine excess. Changes in iodine intake appear to affect the histologic type of thyroid cancer, yet it is unclear whether iodine deficiency or iodine excess increases the overall risk of thyroid cancer.

Deterrence and Patient Education

The agency for toxic substances and disease registry (ATSDR) provides the following patient education information:

• The general public has low exposure levels to iodine.
• Food (iodized salt) is the primary source of exposure.
• The general public is rarely exposed to radioactive iodine unless they have specific tests or treatment of thyroid disease.
• Iodine is both potentially beneficial and harmful.
• Thyroid requires iodine to produce thyroid hormones.
• Exposure to unnecessarily high levels of iodine can result in damage to the thyroid.

This article summarized that iodine toxicity is a rare condition, wherein patients may exhibit vague signs and symptoms – for instance, nausea, vomiting, and diarrhea. While history taking may reveal the toxicity, the cause is difficult to determine without further evaluation.

While the emergency physician is almost always involved in the initial care of patients, it is important to consult with an interprofessional team of specialists that include an intensivist, toxicologist and endocrinologist. The nurses are also a vital part of the interprofessional team as they will monitor the patients vital signs and assist with the education of the patient and family.

The outcomes of iodine toxicity depend on the cause and severity. However, to improve outcomes, prompt consultation with an interprofessional group of specialists is recommended.

Source: StatPearls [Internet]. Updated 2020 Aug 15.