Endocrine Abstracts

Subclinical hyperthyroidism (SHyper) is defined as serum FT₄ and FT₃ levels within their respective reference ranges in the presence of is low or undetectable serum TSH levels. The most common cause of SHyper is exogenous SHyper due to unintentional excessive replacement therapy in hypothyroid patients or to intentional TSH suppressive therapy for malignant thyroid disease. Endogenous SHyper is commonly associated with autonomous thyroid function as occurs in Graves’ disease, multinodular goiter, and solitary autonomously functioning thyroid nodules. The prevalence of SHyper is dependent on age, sex, and to some extent, on the iodine intake of the population. Despite the high prevalence of SHyper and the potential progression to overt disease, the risk associated with this condition is debated.

Opinions are quite divergent regarding the deleterious effects of SHyper on cardiovascular mortality. Several meta-analyses have examined the cardiovascular risk associated with SHyper with the aim of establishing whether treatment should be considered. Their results support the concept that the cardiovascular risk of SHyper depends on the age of the patients and co-morbidity conditions. There is a higher cardiovascular risk in elderly persons with SHyper and potential harmful effects are present in patients with co-morbidity conditions. Most studies on endogenous SHyper and bone health have found a decrease in bone mineral density in postmenopausal women, especially in cortical bone-rich sites, but there is little evidence of a clinically significant effect on bone in premenopausal women. Before treatment is started, it should be established whether the subnormal serum TSH is related to endogenous SHyper and whether it is persistent. Although it has not been demonstrated that early treatment of symptomatic patients with SHyper improves clinical outcome, treatment of SHyper might improve quality of life, cardiovascular risk factors and bone mineral density and would prevent a possible progression to overt disease.