Lithium induced subclinical hypothyroidism
Definition: elevated TSH (thyroid stimulating hormone) in a lithium treated patient, with normal T4 and T3
Prevalence: 6-52% in 11 reports (UptoDate Lithium and the Thyroid, accessed 3.8.2015), average 20-30%
Odds ratio for hypothyroidism on lithium: 5.78
TSH should be tested for every 6-12 months
When does it occur? “usually within the first 6-18 months of treatment” (Managing the Side Effects of Psychotropic Medications, Joseph Goldberg, MD, Carrie Ernst, MD, APP, 2012, page 185)
May be more common in patients with circulating thyroid antibodies (ie, underlying chronic autoimmune thyroiditis; measure antiperoxidase and antithyroglobulin
More common in women
When should supplemental thyroid hormone be added?
1. One option is to monitor TSH more often (every 3 months) but not treat unless TSH levels “exceed 10 mU/L or clinical manifestations emerge”
2. Typical manifestations are “fatigue, anergia, weight gain, poor concentration, depression, cold intolerance, and brittle hair.” (Clinician’s Guide to Bipolar Disorder, David Miklowitz, PhD and Michael Gitlin, MD, Guilford Press, 2014, p. 123)
3. Another option: add thyroid hormone whenever TSH is high (eg, 4-10), especially if there are mood symptoms, or complaints of lethargy and fatigue
How to add:
1. Start with T4 (eg Synthroid, levothyroxine) 0.025 mg/day .
2. Recheck TSH in 6 weeks.
3. If still low, continue to increase by 25 micrograms every 6 weeks, rechecking TSH, until levels have normalized.