What are the considerations for taking lithium in patients with thyroid dysfunction?

Considerations for Lithium Use in Patients with Thyroid Dysfunction

Patients with thyroid dysfunction require careful monitoring and management when taking lithium, as lithium can significantly affect thyroid function and may worsen pre-existing thyroid disorders.

Key Considerations

Pre-existing Thyroid Disorders

• Pre-existing thyroid disorders do not necessarily contraindicate lithium treatment, but require careful monitoring and management 1
• Where hypothyroidism exists, thyroid function should be closely monitored during lithium stabilization and maintenance to allow for correction of changing thyroid parameters 1
• Supplemental thyroid treatment (levothyroxine) may be used when hypothyroidism occurs during lithium therapy 1

Monitoring Requirements

• Baseline thyroid function tests (TSH, free thyroid hormones, specific antibodies, and ultrasonic scanning) should be performed prior to starting lithium 2
• Follow-up thyroid assessment should be repeated at one year after starting lithium 2
• Annual measurements of TSH may be sufficient thereafter to prevent overt hypothyroidism 2
• More frequent monitoring (every 4-6 months) is recommended if TSH is elevated or thyroid autoimmunity is present 2

Risk of Lithium-Induced Thyroid Dysfunction

• Lithium primarily affects thyroid function by inhibiting thyroid hormone release, which can lead to hypothyroidism, goiter, and changes in thyroid texture 2
• Annual rates of newly developed thyroid dysfunction during lithium treatment include: autoimmunity (1.4%), subclinical hypothyroidism (1.7%), and goiter (2.1%) 3
• Women are at higher risk for developing lithium-associated hypothyroidism than men 4
• Hypothyroidism may develop particularly during the first years of lithium treatment 2
• Patients with thyroid autoimmunity have a significantly higher chance of requiring levothyroxine supplementation (41% vs. 6% in those without autoimmunity) 3

Management of Thyroid Dysfunction

• If hypothyroidism develops during lithium treatment, supplemental thyroid hormone (levothyroxine) should be added rather than discontinuing lithium 2
• Even with subclinical hypothyroidism, thyroid hormone replacement should be considered if fatigue or other hypothyroid symptoms are present 5
• Referral to an endocrinologist is necessary if TSH concentrations are repeatedly abnormal, or if goiter or nodules are detected 2

Reversibility After Lithium Discontinuation

• Lithium-associated hypothyroidism appears to be reversible in approximately 41% of patients after lithium discontinuation 6
• If lithium is discontinued in a patient with lithium-induced hypothyroidism, an attempt to discontinue thyroid replacement therapy could be considered 6

Special Situations

Elderly Patients

• Elderly patients are more prone to develop neurotoxicity at higher lithium dosages 1
• Lower starting doses and more careful monitoring may be required in this population 5

Drug Interactions

• Carbamazepine used in combination with lithium may decrease TSH concentrations 3
• Careful monitoring is needed when lithium is combined with other medications that may affect thyroid function 1

Practical Recommendations

• Do not stop lithium solely due to thyroid abnormalities, as lithium is often a critical treatment for reducing mortality in affective disorders 2
• Maintain normal diet, including salt, and adequate fluid intake (2500-3000 mL) during lithium therapy 1
• Educate patients about signs of lithium toxicity (diarrhea, vomiting, tremor, mild ataxia, drowsiness, or muscular weakness) 1
• Consider that thyroid autoimmunity is found in excess among patients with affective disorders, regardless of lithium exposure 2

By carefully monitoring thyroid function and appropriately managing any dysfunction that develops, most patients with thyroid disorders can safely continue lithium therapy when it is clinically indicated.