Thyroid Problems Triggered by Lithium for Bipolar Disease

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Patients with bipolar disorder are often surprised to learn that thyroid problems are a common side effect of taking the drug lithium. Lithium is a common drug used to treat bipolar disorder, which is sometimes referred to as manic depression.

Lithium has several effects on the thyroid:

  • it reduces your thyroid gland's ability to produce thyroxine (T4) 
  • it interferes with the conversion of T4 to T3 
  • it can provoke an increase in the TSH level 
  • it can worsen underlying autoimmune thyroid disease 

Lithium is known to cause goiter (an enlarged thyroid), as well as hypothyroidism (an underactive thyroid), and chronic autoimmune thyroiditis, an inflammatory condition of the thyroid gland. There is also a link between lithium and hyperthyroidism in some patients.

Lithium's Thyroid-Related Side Effects 

Goiter: Goiter, an enlarged thyroid gland, is the most common thyroid-related side effect of lithium, and is estimated to occur in approximately half of all patients treated with lithium. Goiter usually develops within the first two years of lithium treatment. With a lithium-induced goiter, your thyroid can enlarge to as much as twice its normal size.

Hypothyroidism: Hypothyroidism—a deficiency in thyroid hormone—is estimated to occur in up to half of all patients taking lithium. It most often occurs during the first two years of your lithium treatment.

Women over 45 are at greater risk of lithium-induced hypothyroidism, and the overall risk of hypothyroidism in patients treated with lithium increases with age.

The hypothyroidism can be subclinical—with an elevated thyroid stimulating hormone (TSH) level, and normal T4 and T3 levels—with few signs or symptoms.

In some cases, the hypothyroidism is mild, and shows up within the first few months of lithium treatment, but is transient, and thyroid function returns to normal. A small percentage of patients, however, will develop overt hypothyroidism, with its typical signs and symptoms. These patients should be treated for the lithium-induced hypothyroidism.

Autoimmune Thyroiditis: Patients taking lithium are also at risk of developing chronic autoimmune thyroiditis—an autoimmune inflammation of the thyroid gland. If you are just starting lithium therapy, the presence of elevated antithyroid antibodies (thyroid peroxidase TPO antibodies)— even without measurable thyroid dysfunction— puts you at higher risk of developing an overt thyroid condition while being treated with lithium. There also appears to be some evidence that lithium itself can cause elevated antibodies and the onset of autoimmune thyroid disease in some patients.

Lithium treatment also appears to be linked to an increased risk of hyperthyroidism—an excess of thyroid hormone. Several studies have shown that hyperthyroidism is two to three times more prevalent in patients treated with lithium, versus the prevalence in the general population.

What Should Patients Do? 

UpToDate has some advice to help patients taking lithium understand the thyroid-related effects:

Because of the high incidence of goiter and hypothyroidism that occurs during lithium treatment, patients should have a careful thyroid physical examination and determination of serum TSH and antithyroid antibody titers before lithium treatment is begun. Patients with normal thyroid function at that time should be reevaluated every six to 12 months for several years. If thyroid function is abnormal at the initial evaluation, lithium can still be given if necessary but the thyroid dysfunction should be treated.

What this means is that if you are prescribed lithium, you'll need to make sure that you have a thorough clinical thyroid examination, as well as blood tests to measure TSH and antithyroid antibody levels, before you start your lithium therapy. Some experts also recommend having a thyroid evaluation six weeks after you start lithium treatment. As long as you are taking lithium, your doctor should reevaluate your thyroid function, including comprehensive blood tests and a clinical evaluation, every six to 12 months, or earlier, if you begin to show symptoms that suggest you have a thyroid dysfunction.

Lithium-induced hypothyroidism is usually able to be reversed if you stop taking the lithium. If you develop a thyroid problem while on lithium therapy, experts do not recommend stopping your lithium therapy. Instead, they key is to work with your doctor to ensure that you are getting effective treatment for your thyroid condition. Your physician will need to monitor your thyroid and your response to thyroid treatment to ensure you are fully treated, and to periodically evaluate whether continuing with lithium therapy is the best option for your health.

Source:

Goldberg, Joseph, MD. "Management of Hypothyroidism in Patients on Lithium Prophylaxis for Bipolar Disorder." Medscape. October 31, 2008. Online: http://www.medscape.com/viewarticle/581200​

Surks, Martin. "Lithium and the thyroid." UpToDate.  Accessed: March 2009.

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