*4.2.3. Subclinical hyperthyroidism and skeletal changes*

Subclinical hyperthyroidism is defined as subnormal serum TSH with normal serum free thyroid hormones without signs or symptoms of thyrotoxicosis. Its prevalence in the U.S. population has been reported 0.7% (Hollowell et al, 2002). By definition, such patients should not have any clinical abnormalities associated with thyrotoxicosis (Biondi et al, 2005). However, a reduced bone mass was reported among postmenopausal patients (Bauer et al 2001). These observations could thus have a broader impact on the healthcare systems, as the subclinical hyperthyroidism is more frequent than overt thyrotoxicosis (Hollowell et al, 2002). Improvement of bone mineral density was shown in postmenopausal women with subclinical hyperthyroidism after normalization of their thyroid function (Faber et al, 1998). These data would justify indications of treatment in the older population. However, the risk/benefit ratio needs to be demonstrated by long-term, randomized studies.

On the other hand, the bone mineral density of the lumbar spine, femoral neck and the midshaft of the radius were not significantly decreased in premenopausal women (Foldes et al, 1993). The impact of subclinical hyperthyroidism in men is less known. A recent work suggests that a serum TSH concentration at the lower end of the reference range may be associated with low BMD in men (Kim et al, 2010).
