Exophthalmos and elevated thyroxine levels in association with lithium therapy

Area of Science:

• Endocrinology
• Pharmacology
• Thyroidology

Background:

• Lithium carbonate is a common treatment for bipolar disorder.
• Thyroid dysfunction, including goiter and hypothyroidism, is a known side effect of lithium therapy.
• However, hyperthyroidism and exophthalmos associated with lithium are rare.

Observation:

• A 62-year-old male patient developed rapid-onset exophthalmos (protruding eyes).
• He also exhibited elevated circulating thyroxine (T4) levels, elevated thyroid-stimulating hormone (TSH), and increased radioiodine uptake.
• These symptoms emerged within six weeks of re-initiating lithium carbonate treatment.

Findings:

• Discontinuation of lithium carbonate led to normalization of all thyroid function indices.
• The patient's exophthalmos resolved from 22mm to 17mm after stopping lithium.
• The study suggests lithium decreases thyroid hormone secretion, leading to TSH elevation.

Implications:

• The patient's pituitary may have been refractory to thyroxine's inhibitory feedback due to normal triiodothyronine (T3) levels.
• This refractory state could have caused continued TSH hypersecretion, resulting in lithium-induced hyperthyroidism.
• This case highlights a rare but significant adverse effect of lithium carbonate on thyroid function.