Review of the risks and/or benefits of thyroxine treatment in ‘mild’ subclinical hypothyroidism

Abstract

Subclinical hypothyroidism (SCH) is a form of mild thyroid failure and is a commonly encountered condition in clinical practice. It denotes the presence of a raised serum thyroid stimulating hormone (TSH) and normal serum free thyroid hormone concentrations (tri-iodothyronine [T3] and thyroxine [T4]). ‘Mild’ subclinical hypothyroidism is associated with a TSH level between 4.5-9mIU/L (0.4-4.2) whereas patients with a serum TSH level ?10mIU/L are classified as having the ‘severe’ form. The clinical significance of this condition has aroused a lot of interest over the last decade, especially its effects on various health outcomes (namely cardiovascular disease, lipid metabolism, fertility, pregnancy outcomes and fetal neurocognitive function). Unfortunately the unavailability of adequately powered, double-blind randomised controlled studies precludes the availability of clear cut guidelines as to how one should treat subclinical hypothyroidism. This review looks at the available evidence for and against treatment of SCH with levothyroixine. Most authors agree on the use of clinical judgement as well as individualising management based on the underlying unique patient characteristics when it comes to formulating a management plan for this condition.