The impact of thyroid autoimmunity (TPOAb) on bone density and fracture risk in postmenopausal women

Skeletal development, linear growth, cartilage biology and bone turnover are highly dependent on the activity of thyroid hormones. Thyroid dysfunction affects the skeleton, and autoimmune thyroid disease, manifesting as a chronic inflammatory condition, may be an important contributing factor to impaired bone quality in these patients.

Measurement of TSH, FT4, TPOAb and bone mineral density and FRAX score calculations were performed in 189 postmenopausal women (110 euthyroid women and 79 women diagnosed with subclinical hypothyroidism) divided into subgroups according to the presence of TPOAb.

In multivariate logistic regression analysis only TPOAb were found to be significantly related to fracture, independently of TSH values (p=0.018; OR=7.800; 95% CI 1.424-42.721). Lower bone mineral density and FRAX score for hip and for major osteoporotic fractures were associated with the presence of TPOAb in euthyroid postmenopausal women in an unadjusted logistic regression model, as well as in a model adjusted for age, BMI and smoking. TSH was a better predictive factor for fractures in women with subclinical hypothyroidism (FRAX main p <0.001; 95% CI for SE 0.858-0.959 and FRAX hip p <0.001; 95% CI for SE 0.628-0.854).

Autoimmune thyroid disease is associated with decreased bone mineral density at both spine and hip and risk of future fracture incidence in euthyroid postmenopausal women. Presence of TPOAb is a potential marker of higher fracture risk in these patients. However, in subclinical hypothyroidism, TSH is a better indicator of future fragility fractures than TPOAb.