Background/Purpose:

Hyperthyroidism has been described as a risk factor for poor bone health.^{1, 2} The FRAX^TM tool has been used to identify the ten year risk of fracture by utilising hip bone mineral density (BMD) only. If hyperthyroidism is predominantly associated with bone loss in the lumbar spine, the fracture risk in these patients may have been underestimated. No previous study has examined the differential amount of bone loss in hyperthyroidism. This study will determine the extent and site of bone loss in patients with primary hyperthyroidism compared to controls, looking at lumbar spine and femoral neck BMD.

Methods:

Using a nested case-control approach, a cohort of patients referred between 2004 and 2011 for a dual-energy x-ray absorptiometry scan with hyperthyroidism as their main risk factor was identified. These were then age and gender matched with controls referred in the same time period with no indication for scanning. Sites of bone loss were ascertained by comparing the BMD in two areas (L1-L4 vertebrae and the left femoral neck) between cases and controls, using students T-test. A logistic model was then fitted to determine the odds of having a significantly reduced BMD with a diagnosis of hyperthyroidism. The fit of the model was tested using receiver operating characteristic (ROC) curves.

Results:

232 patients with current hyperthyroidism were identified, comprising 184 females (79.7%), with a mean age of 62 (SD 10.7). 232 controls were age and sex matched. Simple comparisons between cases and controls were identified using the students t-test; mean difference between L1-L4 BMD was 0.085 g/cm² (95% CI 0.051- 0.119) and femoral neck BMD difference was 0.057 g/cm²(95% CI 0.031- 0.083); both had a p-value ≤0.001. The odds of having a significantly reduced BMD was found to be greater in the femoral neck, with an odds ratio of  19.4 for femoral neck BMD (95% CI 4.8-79.0)  compared with 12.2 for L1-L4 BMD (95% CI 4.3-34.8). When the area under the ROC curve was calculated for both L1-L4 and femoral neck BMD, the result was a similar sensitivity and specificity, with an area under the ROC curve of 0.63 for L1-L4 BMD, and an area of 0.62 for the femoral neck.

Conclusion:

Both hip BMD and lumbar spine BMD are significantly reduced in thyrotoxic patients- while BMD loss was found to be greater in the femoral neck than in the lumbar spine, this was only marginally more. Further analysis looking at whether this risk factor has more implications on fracture risk than those used in the FRAX^TM tool is needed.

References:

1.            Gogakos AI, Duncan Bassett JH, Williams GR. Thyroid and bone. Archives of Biochemistry and Biophysics. 2010;503(1):129-36.

2.            Nicholls JJ, Brassill MJ, Williams GR, Bassett JHD. The skeletal consequences of thyrotoxicosis. Journal of Endocrinology. 2012;213(3):209-21.

---

« Back to 2013 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-effects-of-hyperthyroidism-on-bone-mineral-density-at-different-sites-an-observational-case-control-study/