Subclinical hyperthyroidism.

Purpose of review: Subclinical hyperthyroidism is a clinical condition where thyroid-stimulating hormone (TSH) is below the normal range along with normal levels of circulating thyroid hormones. It is associated with cardiovascular complications such as atrial fibrillation, but the effects on other organ systems is less certain. There are areas of uncertainty in the management of this condition, which this review seeks to address by reviewing relevant literature from the last 18 months.

Recent findings: Data on prevalence from recent meta-analyses are in line with previous studies. Individual TSH reference ranges are influenced by genetic factors, which suggests that current reference ranges may be leading to misdiagnosis. Further research has increased the strength of evidence for the association with atrial fibrillation. A meta-analysis has shown increased risk of osteoporosis and fractures. Data support an association between subclinical hyperthyroidism and dementia. A randomised controlled trial has recently been conducted to investigate the effect of treatment on atrial fibrillation incidence, in which post hoc-analysis showed normalisation of TSH decreased risk of atrial fibrillation.

Summary: Degree of TSH suppression is an important element of clinical assessment. Subclinical hyperthyroidism is associated with atrial fibrillation, osteoporosis and dementia. Further research in this field is warranted.