LT4/LT3 Combination Therapy Versus LT4 Monotherapy in Patients with Autoimmune Hypothyroidism.

Hypothyroidism is common, affecting 5% of the general population, for which levothyroxine (LT4) monotherapy is the standard treatment. Despite normalized serum thyroid hormone levels, 10-15% of LT4 treated patients have various persistent complaints, the most important of which is tiredness. This could be explained by the fact that physiological T4/T3 ratios cannot be reached with LT4 monotherapy, as in a healthy individual T3 is not only derived from T4/T3 conversion but is also directly produced by the thyroid itself. Studies have reported contradicting results as to whether addition of liothyronine (LT4/LT3 combination therapy) in patients with persistent tiredness on LT4 monotherapy is effective or not. Studies have suggested higher effectiveness in patients carrying genetic variation in the type 2 deiodinase (DIO2-rs225014) and monocarboxylate transporter 10 (MCT10-rs17606253) genes. Objective: To investigate whether addition of liothyronine (LT4/LT3 combination therapy) in in patients with persistent tiredness on LT4 monotherapy is effective or not in relieving tiredness.