Drug-induced hypothyroidism
Definition
Drug-induced hypothyroidism is an underactive thyroid gland due to a reaction from medication. "Drug-induced" means caused or brought on by medication.
Causes
Drug-induced hypothyroidism may be caused by:
- Drugs used for hyperthyroidism (overactive thyroid), such as propylthiouracil (PTU), radioactive iodine, potassium iodide, and methimazole
- Treatment with lithium or iodides in certain people
Unusual causes of drug-induced hypothyroidism include:
- Amiodarone
- Eating a large amount of iodine-containing seaweed
- Nitroprusside
- Perchlorate
- Povidone iodine (Betadine)
- Sulfonylureas
Too much iodine may cause either hyperthyroidism or hypothyroidism. For example, iodine used by the mother during pregnancy (or as an antiseptic in the delivery room) can cause the fetus or newborn to develop goiter (enlarged thyroid gland). This can cause temporary hypothyroidism.
The most severe form of hypothyroidism is called myxedema coma. This is a medical emergency. Severe hypothyroidism, however, is rarely related to drugs.
Symptoms
Early symptoms:
Late symptoms:
- Decreased hearing ability
- Hoarseness
- Menstrual disorders
- Puffy face, hands, and feet
- Slow speech
- Thickening of the skin
- Thinning of eyebrows
Joint stiffness may also occur.
Exams and Tests
A physical examination may reveal an enlarged thyroid gland. Other signs may include:
- Low blood pressure
- Low temperature
- Slow heart rate
A chest x-ray may show an enlarged heart.
Blood tests to determine thyroid function include:
Other abnormalities that may be discovered in the laboratory include:
Treatment
Stop taking the drug causing the hypothyroidism, if possible. However, do not stop taking prescribed medications without first talking to your healthcare provider. Some drugs may cause unpleasant or even life-threatening reactions if not stopped gradually or replaced.
Levothyroxine, a thyroid replacement hormone, is the most commonly used medication to treat this condition. The dose is adjusted to bring TSH to normal levels. After you have started replacement therapy, report symptoms of increased thyroid activity (hyperthyroidism):
If a period of lowered thyroid activity has led to weight gain, a high-fiber, low-calorie diet and moderate activity can help relieve constipation and promote weight loss.
Outlook (Prognosis)
With early treatment, your condition should return to normal. However, hypothyroidism will return if the replacement therapy is not continued. Myxedema coma can result in death.
Possible Complications
Myxedema coma, the most severe form of hypothyroidism, is rare. It can be caused by an infection, illness, exposure to cold, or certain medications. Symptoms and signs of myxedema coma include:
Other complications of hypothyroidism are:
When to Contact a Medical Professional
Call your health care provider if you have symptoms of hypothyroidism.
Prevention
Medications that can cause hypothyroidism should be used with caution. If you take such medicines, you are usually monitored closely. For example, your thyroid levels may be checked every once in a while.
Review Date:
6/17/2008
Reviewed By:
Elizabeth H. Holt, MD, PhD, Assistant Professor of Medicine, Section of Endocrinology and Metabolism, Yale University. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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