Lithium's Masking of Thyroid Biomarkers in a Hyperthyroid State
Poster #: 061
Session/Time: B
Author:
Baylee Elise Marin, BS
Mentor:
David Spiegel, MD
Research Type: Case Report
Abstract
INTRODUCTION:
Lithium is a mood stabilizing medication used primarily in the treatment of bipolar disorder I and II that is proven to be particularly useful in treating and preventing relapse of manic symptoms. There are many known side effects that require routine monitoring, including kidney damage, cardiac effects, and hypothyroidism. Lithium decreases thyroxine (t4) produced endogenously by the thyroid gland by building up to toxic levels in thyroid tissue, while also decreasing peripheral conversion of thyroxine (t4) to the active form triiodothyronine (t3) by deiodinases.
CASE INFORMATION:
A 62 year old female with a past medical history of schizoaffective disorder, bipolar disorder, multinodular goiter s/p total thyroidectomy, and substance abuse presented to the hospital for shortness of breath and altered mental status. On physical exam, the patient was found to be tachypneic, tachycardic, anxious, and suffering diffuse weakness and a tremor. The patient was on levothyroxine 125 mg after having a total thyroidectomy four months prior. Her thyroid stimulating hormone (tsh) was 0.01, so there was concern for levothyroxine overdose as her clinical presentation and tsh supported a hyperthyroid state, and she struggled to recall her medications and dosing. However, her t4 level was within normal limits at 1.4, and t3 was very low at 1.4. While t4 can often be normal in a hyperthyroid state, the t3 level was certainly incongruent. However, the patient had been chronically on lithium for her bipolar disorder, so it was suspected the lithium could be causing the low t3 level. The patient's lithium was discontinued on hospital day 2 after evaluation from psychiatry. The patient's levothyroxine dosage was also monitored, and her symptoms eventually cleared up.
DISCUSSION/CLINICAL FINDINGS:
This case highlighted the ability of lithium's effect on thyroid hormone to hide certain biochemical markers of hyperthyroidism. While it is well known that lithium can cause hypothyroidism in euthyroid individuals, there is paucity in research detailing how lithium can affect the thyroid biomarkers in an athyreotic patient taking supplemental t4, or a patient with potential thyroid overdose. This patient's low tsh and physical symptoms were consistent with hyperthyroidism, despite her t4 being within normal limits and her t3 being very low. Even with normal levels of t4, thyroid levels and feedback is very individualized and varying levels can lead to clinical symptoms and low tsh, however free t3 tends to rise before t4. Lithium, even at subtherapeutic levels, decreases the peripheral conversion of t4 to t3, explaining why her t3 was so low.
CONCLUSION:
While it is standard practice to monitor the thyroid function of patients on lithium, the common concern with the medication is the toxic buildup of the medication in the thyroid tissue and its interference with endogenous production. This case showed that the effects of lithium on peripheral deiodination can greatly influence the thyroid function of athyreotic individuals on supplemental t4, and mask certain biomarkers in a patient experiencing thyroid overdose, further emphasizing the importance of monitoring thyroid function in patients taking lithium.
Lithium is a mood stabilizing medication used primarily in the treatment of bipolar disorder I and II that is proven to be particularly useful in treating and preventing relapse of manic symptoms. There are many known side effects that require routine monitoring, including kidney damage, cardiac effects, and hypothyroidism. Lithium decreases thyroxine (t4) produced endogenously by the thyroid gland by building up to toxic levels in thyroid tissue, while also decreasing peripheral conversion of thyroxine (t4) to the active form triiodothyronine (t3) by deiodinases.
CASE INFORMATION:
A 62 year old female with a past medical history of schizoaffective disorder, bipolar disorder, multinodular goiter s/p total thyroidectomy, and substance abuse presented to the hospital for shortness of breath and altered mental status. On physical exam, the patient was found to be tachypneic, tachycardic, anxious, and suffering diffuse weakness and a tremor. The patient was on levothyroxine 125 mg after having a total thyroidectomy four months prior. Her thyroid stimulating hormone (tsh) was 0.01, so there was concern for levothyroxine overdose as her clinical presentation and tsh supported a hyperthyroid state, and she struggled to recall her medications and dosing. However, her t4 level was within normal limits at 1.4, and t3 was very low at 1.4. While t4 can often be normal in a hyperthyroid state, the t3 level was certainly incongruent. However, the patient had been chronically on lithium for her bipolar disorder, so it was suspected the lithium could be causing the low t3 level. The patient's lithium was discontinued on hospital day 2 after evaluation from psychiatry. The patient's levothyroxine dosage was also monitored, and her symptoms eventually cleared up.
DISCUSSION/CLINICAL FINDINGS:
This case highlighted the ability of lithium's effect on thyroid hormone to hide certain biochemical markers of hyperthyroidism. While it is well known that lithium can cause hypothyroidism in euthyroid individuals, there is paucity in research detailing how lithium can affect the thyroid biomarkers in an athyreotic patient taking supplemental t4, or a patient with potential thyroid overdose. This patient's low tsh and physical symptoms were consistent with hyperthyroidism, despite her t4 being within normal limits and her t3 being very low. Even with normal levels of t4, thyroid levels and feedback is very individualized and varying levels can lead to clinical symptoms and low tsh, however free t3 tends to rise before t4. Lithium, even at subtherapeutic levels, decreases the peripheral conversion of t4 to t3, explaining why her t3 was so low.
CONCLUSION:
While it is standard practice to monitor the thyroid function of patients on lithium, the common concern with the medication is the toxic buildup of the medication in the thyroid tissue and its interference with endogenous production. This case showed that the effects of lithium on peripheral deiodination can greatly influence the thyroid function of athyreotic individuals on supplemental t4, and mask certain biomarkers in a patient experiencing thyroid overdose, further emphasizing the importance of monitoring thyroid function in patients taking lithium.