Search

The widespread use of thyroid tests in asymptomatic individuals identifies many patients with transient subclinical hypothyroidism.Our objective was to determine the effect of seasonal change on serum TSH levels and the transition between subclinical hypothyroid and euthyroid status.This was a retrospective longitudinal study of 1751 subclinical hypothyroid and 28 096 euthyroid subjects aged over 18 years who underwent serial thyroid function tests at a health screening center between October 2003 and May 2011.Age-adjusted geometric mean values of the TSH level by month were calculated using linear mixed models. Adjusted odds ratios of test season and multiple baseline clinical factors were determined using generalized estimating equations.During a median 36 months of follow-up, 57.9% of subclinical hypothyroid subjects reverted to euthyroidism, and 4.3% of euthyroid subjects developed subclinical hypothyroidism. The monthly distribution of follow-up TSH levels indicated a biphasic pattern, ie, an increase during the winter-spring season and a decrease during the summer-fall season, with a maximal TSH difference of 0.69 mIU/L in subclinical hypothyroid and 0.30 mIU/L in euthyroid subjects. Normalization of subclinical hypothyroidism was increased 1.4-fold in follow-up tests during the summer-fall follow-up, whereas subclinical hypothyroidism increased 1.4-fold in euthyroid subjects during the winter-spring follow-up.The season in which thyroid testing was performed was independently related to the transition between subclinical hypothyroid and euthyroid status. Seasonal variations in TSH concentration should be considered before deciding on treatment of subclinical hypothyroidism, particularly in the areas with a wide annual temperature range.

To assess the changes in bone mineral density and osteoblastic activity in patients with hyperthyroidism and to investigate the relationship between those changes, we measured bone mineral density and serum osteocalcin in 109 patients with Graves' disease, comprising 75 untreated patients and 34 patients under treatment, and 200 normal controls. The degree of change in bone mineral density was quantified with Z transformation, in which we used means and SDs of bone mineral densities obtained in the process of age- and sex-matched 1:1 pairing developed by ourselves. Bone mineral density was low in female patients with hyperthyroidism in the spine, femur neck, trochanter, and Ward's triangle, but was not low in male patients. Serum osteocalcin was elevated in patients with untreated Graves' disease and correlated negatively with the Z values of bone mineral densities of the spine, femur neck, and trochanter. In conclusion, indices of osteoblastic activity were elevated in patients with hyperthyroidism, probably secondary to a thyroid hormone-induced increase in bone resorption which resulted in reduced bone mineral density. Quantification of the change in bone mineral density by using the parameters derived in the process of age- and sex-matched pairing seems to be an efficient method for statistical analyses.