Does a psychiatrist initiate thyroid hormone replacement therapy, such as levothyroxine, in a patient with potential hypothyroidism (underactive thyroid) taking lithium, or refer them to a primary care provider or endocrinologist?

Psychiatrists Should Refer Lithium-Induced Hypothyroidism to Primary Care or Endocrinology

Psychiatrists should not initiate thyroid hormone replacement therapy themselves but should refer patients with lithium-induced hypothyroidism to primary care physicians or endocrinologists for management. While psychiatrists are responsible for monitoring thyroid function in patients on lithium, the actual initiation and management of levothyroxine therapy falls outside the typical scope of psychiatric practice and requires expertise in thyroid hormone management 1.

Rationale for Referral

Complexity of Thyroid Hormone Management

• Levothyroxine dosing requires careful titration based on multiple patient-specific factors including age, cardiac status, and comorbidities, with initial doses ranging from 25-50 mcg/day in elderly or cardiac patients to full replacement doses of 1.6 mcg/kg/day in younger patients 1.
• TSH monitoring must occur every 6-8 weeks during dose titration, with dose adjustments of 12.5-25 mcg based on response, requiring expertise in interpreting thyroid function tests and managing potential complications 1.
• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, fractures, and cardiac complications 1.

Critical Safety Considerations Beyond Psychiatric Expertise

• Before initiating levothyroxine, concurrent adrenal insufficiency must be ruled out, as starting thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis 1.
• Patients over 70 years or with cardiac disease require starting doses of 25-50 mcg/day with gradual titration to avoid unmasking cardiac ischemia or precipitating arrhythmias 1.
• Overtreatment occurs in 14-21% of treated patients and increases risk for atrial fibrillation (3-5 fold), osteoporosis, and cardiovascular mortality, particularly in patients over 60 years 1.

Psychiatrist's Role in Lithium-Induced Hypothyroidism

Baseline and Ongoing Monitoring

• Thyroid function tests (TSH, free T4, and thyroid autoantibodies) should be performed at baseline before initiating lithium therapy and then annually during treatment 2.
• More frequent assessment is recommended for middle-aged females (≥50 years), patients with family history of thyroid disease, and those positive for thyroid autoantibodies 2.
• Lithium-induced hypothyroidism develops most often during the first two years of treatment, with 55% of cases diagnosed within the first year and 74% within two years 3.

Recognition and Referral Triggers

• Hypothyroidism occurs in approximately 20% of women on long-term lithium therapy, with no men affected in some studies 4.
• All cases of lithium-induced hypothyroidism show elevated TSH levels, making TSH the laboratory examination of choice for detection 4.
• When TSH is persistently >10 mIU/L or when patients develop hypothyroid symptoms with any degree of TSH elevation, immediate referral for levothyroxine therapy is indicated 1.

Continuation of Lithium During Treatment

Lithium Should Not Be Discontinued

• Hypothyroid patients responding well to lithium treatment should continue their medication combined with appropriate thyroxine substitution 4.
• Lithium affects thyroid function through multiple mechanisms including decreased thyroid hormone synthesis and release, and decreased peripheral deiodination of T4 2.
• The development of hypothyroidism is not an indication to discontinue lithium if the psychiatric condition is well-controlled 4.

Common Pitfalls to Avoid

• Never attempt to manage thyroid hormone replacement without appropriate training, as the complexity of dosing, monitoring, and managing complications requires endocrine expertise 1.
• Do not delay referral when TSH >10 mIU/L, as this level carries approximately 5% annual risk of progression to overt hypothyroidism and warrants treatment regardless of symptoms 1.
• Avoid assuming hypothyroidism requires lithium discontinuation, as combined therapy with levothyroxine and lithium is the standard approach 4.
• Do not treat based on a single elevated TSH value, as 30-60% of elevated TSH levels normalize on repeat testing; confirm with repeat measurement after 3-6 weeks 1.