Jacobs Journal of Internal Medicine

Subclinical Hyperthyroidism: Clinical Consequences and Management

*Avraham Ishay
Department Of Medicine, Endocrine Institute, Israel

*Corresponding Author:
Avraham Ishay
Department Of Medicine, Endocrine Institute, Israel
Email:ishayav@netvision.net.il

Published on: 2016-08-04

Abstract

Background: Subclinical hyperthyroidism (Shyper) is a common clinical entity which represents a condition of mild thyroid over-activity. Whether or not Shyper should be treated remains a matter of debate, despite the body of evidence that demonstrates an association between this condition and significant adverse effects.
Summary: After an overview of the etiology, differential diagnosis, epidemiology and natural history of Shyper, this review will focus on the clinical outcomes related to this condition, i.e., cardiovascular morbidity and mortality, bone health, mood and cognitive function. The treatment options of Shyper are essentially the same as overt hyperthyroidism. Notwithstanding the lack of appropriately designed prospective studies, we provide a practical framework to effectively manage Shyper.
Conclusion: Treatment of Shyper should be considered after evaluating four critical parameters: age>65 years, the degree of TSH suppression (TSH <0.1mU/L), the presence of clinical thyroid abnormalities and underlying relevant co-morbidities.

Keywords

Subclinical hyperthyroidism; Treatment; Cardiovascular risk; Atrial fibrillation; Osteoporosis

Introduction

Subclinical hyperthyroidism (SHyper) has been increasingly recognized due to availability of thyroid functioning tests, as a condition characterized by a low or undetectable concentration of serum thyrotropin (TSH) with normal free thyroxine (FT4) and free triiodothyronine (FT3) levels. This entity has emerged due to the increase in sensitivity of TSH assays. Third-generation assays, which have a functional sensitivity of 0.01-0.02 are able to discriminate between complete and incomplete TSH suppression. The pituitary gland is extremely sensitive to small changes in thyroid hormone levels. TSH and FT4 have a negative log-linear relationship such that small changes in FT4 levels results in large changes in TSH levels. Although thyroid hormone levels are, by definition, within the normal range in SHyper, they are often near the upper limit of the reference range. In fact, in some individuals, serum thyroid hormones concentrations in the normal range are sufficiently high to suppress TSH and produce adverse tissue effects. Actually, TSH is more sensitive than FT4 for assessing mild thyroid function excess. Moreover, interindividual differences in the thyroid-pituitary set point, which are genetically determined, may explain the different peripheral thyroid hormone effects in subjects with the same hormonal setting, thus the distinction between SHyper and hyperthyroidism is somewhat artificial.