From the Guidelines
Lithium therapy requires regular monitoring of thyroid function tests (TFTs) due to its potential to cause hypothyroidism, with baseline assessments and follow-up monitoring every 3-6 months recommended. The effect of lithium on TFTs is a significant concern, as it can lead to hypothyroidism in a substantial proportion of patients, with some studies suggesting a prevalence of 20-30% 1. Lithium's mechanism of action on the thyroid gland involves inhibiting thyroid hormone release and synthesis, resulting in elevated thyroid-stimulating hormone (TSH) levels and decreased free T4 and T3 levels.
- Key considerations for monitoring lithium's effect on TFTs include:
- Baseline TFTs before starting lithium therapy
- Regular monitoring every 3-6 months during the first year of treatment
- Annual monitoring thereafter
- More frequent monitoring for patients with pre-existing thyroid conditions or a family history of thyroid disorders
- If hypothyroidism develops, levothyroxine supplementation can be initiated, typically starting at 25-50 mcg daily, with titration based on TSH levels, allowing lithium therapy to continue without interruption 1.
From the FDA Drug Label
Thyroid Abnormalities: Euthyroid goiter and/or hypothyroidism (including myxedema) accompanied by lower T3 and T4. The effect of lithium on Thyroid Function Tests (TFTs) is that it can cause hypothyroidism accompanied by lower T3 and T4 levels.
- Lithium use has been associated with euthyroid goiter and/or hypothyroidism.
- T3 and T4 levels may be lower in patients taking lithium. 2
From the Research
Effect of Lithium on Thyroid Function Tests (TFTs)
- Lithium therapy can affect thyroid function, leading to changes in TFTs, including thyroxine (T4), triiodothyronine (T3), thyroid-stimulating hormone (TSH), and free T4 index 3.
- Studies have shown that lithium can decrease thyroid hormone synthesis and release, and increase the propensity to thyroid autoimmunity in susceptible individuals 4.
- The most common thyroid abnormalities associated with lithium therapy are hypothyroidism and goitre, with hyperthyroidism being less frequent 4, 5.
- Subclinical hypothyroidism is a common condition in patients on lithium therapy, and may be associated with somatic and neuropsychiatric symptoms 6.
Monitoring of Thyroid Function in Patients on Lithium Therapy
- Regular monitoring of thyroid function is essential in patients on lithium therapy, with recommendations for baseline and annual assessments of TFTs, including TSH, free thyroid hormones, and thyroid auto-antibodies 4, 5.
- More frequent assessments may be necessary in certain patient populations, such as middle-aged women, those with a family history of thyroid disease, and those positive for thyroid auto-antibodies 4.
- The use of ultrasonic scanning to assess thyroid size and texture may also be useful in monitoring patients on lithium therapy 5.
Clinical Significance and Management of Lithium-Induced Thyroid Abnormalities
- Lithium-induced thyroid abnormalities can have significant clinical consequences, including somatic and neuropsychiatric symptoms, and may interfere with treatment responsiveness 6.
- Guidelines for the evaluation and treatment of lithium-associated subclinical hypothyroidism have been proposed, including recommendations for thyroxine supplementation in patients with elevated TSH levels 6.
- Thyroid function abnormalities should not constitute an outright contraindication to lithium treatment, and decisions regarding treatment should be made on a case-by-case basis, taking into account the potential benefits and risks of lithium therapy 5.