A young woman who has had a relatively good response to low dose lithium treatment has labs that suggest she may be developing hypothyroidism (low thyroid) and asks what her options are. What can be done to treat the problem? What risks are there for developing it? And what would happen if she decided to taper off the lithium, would her thyroid return to normal.
We have some good answers for many but not all of her questions.
First, what are the odds of developing some symptoms of low thyroid on lithium. It turns out that, like thyroid disease in general, the risk is much higher for woman. Perhaps 18% of women on lithium will develop some evidence for low thyroid function. Between 5 and 10% of men will develop signs of low thyroid.
In her case, as with many women who develop thyroid problems on lithium, she has a family history of thyroid disease in her mother and her mother’s mother. We did not check thyroid antibodies, but they might have been elevated, which would be consistent with the most common type of low thyroid on lithium – unmasking an underlying tendency to low thyroid.
This occurs because lithium interferes with the creation of thyroid hormone in response to stimulation by TSH from the brain. As a result, the first sign of this problem is a risking TSH as the brain tries to overcome this lithium effect. For most people that works fine and a small bump (not measurable on our tests) in TSH overcomes the effect of lithium and thyroid function remains normal.
We also know that there is a relationship between low thyroid and bipolar. Studies of bipolar patients not treated with lithium find a doubling of the rate of low thyroid compared with the general population. Consistent with
Hypothyroidism risk in bipolar patients with different treatments. All were higher than the general population.
that, studies find that all treatments for bipolar are associated with some increase in risk of low thyroid. Not because the treatments necessarily cause low thyroid, but just because they are given to people with bipolar, who are at higher risk of thyroid problems.
So what will happen if she stops lithium now? We know that within about two weeks of stopping lithium there will be an increased output of thyroid hormone. We don’t know if this will return her back to normal, but it probably will, since she has only been taking lithium for a short while.
Had she been taking lithium for longer the low thyroid hormone level would be less likely to return to normal.
There is however some good news, we also know that this is not a progressive problem. Low thyroid in patients on lithium shows up within the first six months and reaches its peak (a modest effect on thyroid function) within two years. After that thyroid function remains the same no matter how long the person takes lithium.
We also know that this is an easy problem to treat. A low dose of levothyroxine, or other thyroid hormone replacement solves the problem for nearly everyone with no apparent adverse effects.
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