Thyroid Replacement Therapy: The Hidden Challenges

Abstract

Hypothyroidism has a gradual onset and non-specific symptoms, which might be subtle, and which might therefore be ignored or misdiagnosed. Subclinical hypothyroidism is a well-established phenomenon where a patient does not have thyroid symptoms, but shows biochemical evidences of hypothyroidism. However, diagnosis and treatment of these patients may prevent development of overt hypothyroidism and cardiovascular symptoms. Replacement therapy with levothyroxine (T4) is the treatment of choice for hypothyroidism; levothyroxine is taken daily, provides stable plasma levels and is suitable for the majority of patients. Patients with certain forms of hypothyroidism -central hypothyroidism, thyroidectomy patients and patients with "low T3 syndrome" -may benefit from treatment with liothyronine (T3), which is more potent and has a shorter onset of action. The use of liothyronine in combination with levothyroxine is controversial, but there is evidence that some patients, particularly those with deiodinase 2 and thyroid hormone transporter expression polymorphisms, may benefit from combination therapy.