Understanding of subclinical hyperthyroidism?

Subclinical hyperthyroidism may increase the risk of fractureA study published in the May 26, 2015 issue of the Journal of the American Medi


Subclinical hyperthyroidism may increase the risk of fracture

A study published in the May 26, 2015 issue of the Journal of the American Medical Association (JAMA), meta, showed an increased risk of hip and other fractures in patients with subclinical hyperthyroidism.

The meta analysis included a total of 13 prospective cohort studies involving 70298 subjects, including 4092 patients with subclinical hypothyroidism and two patients with subclinical hyperthyroidism ().

Subclinical hyperthyroidism is defined as the level of thyroid stimulating hormone (TSH), 0.45mIU/L, and free thyroxine (FT4) levels within the normal reference range. The researchers found that, adjusted for age, sex, and other risk factors after fracture, compared with subjects with normal thyroid function, subclinical hyperthyroidism in patients with hip fracture risk increased 36%, 28% increase in the risk of fractures occur in other parts of the body. In addition, subclinical hyperthyroidism was associated with an increased risk of non pyramidal fractures by 16%. In addition, men with subclinical hyperthyroidism had a 3.5 fold increase in the risk of fracture, but there was no significant increase in the risk of fracture in women with subclinical hyperthyroidism.

The study also found that a decrease in TSH levels was associated with an increased incidence of fractures. For patients with TSH levels of 0.10mIU/L, a 61% increase in hip fracture risk was associated with an increased risk of fracture of the cone by more than a factor of 3.5.

This study did not find any correlation between subclinical hypothyroidism and the risk of fracture and to accept the baseline thyroxine treatment did not receive thyroxine treatment patients were compared, there is no obvious effect of levothyroxine treatment on fracture prognosis.

The Affiliated Hospital of University of Bern, Dr. Manuel R. of Switzerland Blum said, "in the prospective cohort study, the subjects are often mixed with overt thyroid disease, thyroid dysfunction patients and patients with fracture of the sample size and included too small on subclinical thyroid dysfunction and the relationship between the fracture risk differences still exist.

Dr. Blum and others have proposed three possible mechanisms to explain how thyroid dysfunction affects fracture risk.

First of all, the thyroid hormone has been shown to influence osteoclast and osteoblast function, when the level of thyroid hormone in the upper limit of the normal range, may lead to accelerated bone turnover, resulting in the loss of bone mass, increase the risk of fracture.

Subclinical hyperthyroidism can also increase the risk of falls by affecting muscle strength and coordination.

In addition, patients with subclinical hyperthyroidism often have no specific clinical symptoms and may have been delayed for years before diagnosis. However, this phenomenon may lead to the extension of the clinical effect of subclinical hyperthyroidism on bone metabolism.

Dr. Blum also pointed out the deficiencies of these observational data, for example, most of the studies only at baseline thyroid function assessment of subjects, but in the entire study period, some patients may progress to overt thyroid dysfunction; and among different cohorts lack of unified definition of small fracture.

Current guidelines recommend that any 65 years of age or older with subclinical hyperthyroidism and TSH levels continued to < 0.1mIU/L patients have to receive treatment, and for those TSH level than 0.1mIU/L, but lower than the normal range of patients, should be considered for treatment. Dr. Blum noted that their findings further support the current guidelines.



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