Impact of Thyroid Disease on Bone Mineral Density Preservation in Patients With Osteoporosis and Idiopathic Hypercalciuria

Background: Idiopathic hypercalciuria (IHC) is associated with reduced bone mineral density (BMD) and increased risk of osteoporotic fractures. It is not known if thyroid disease impacts the degree of urine and bone mineral abnormalities in patients with IHC and osteoporosis (OPO). Methods: Retrospective chart review from a private endocrinology clinic identified 62 consecutive patients with OPO (fragility fracture and/or t-score ≤-2.5 on bone density scan) and concomitant diagnosis of IHC (urine calcium > 4.0 mg/kg weight/d when intaking low-moderate calcium amounts). Patients were classified into two groups: those with thyroid disease (Thy+, if presence of autoimmune thyroid disease [AITD] with high antibody titers and/or long-term thyroid medication use) and those without (Thy-). Comparisons were made between the two groups for severity of renal disease (urine calcium) and bone disease (number of fragility fractures, and BMD response to therapy). Results: Of 55 women and 7 men identified with both OPO and IHC, 30 were Thy+ (4 with Graves’, 11 with confirmed Hashimoto’s, 13 taking levothyroxine for presumed Hashimoto’s and 2 with thyroid cancer), and 32 were Thy- (including 2 with type 1 DM, 1 with vitiligo, and 6 with non-toxic nodular goiters requiring biopsies). Thy+ were compared to Thy- with respect to: mean age (70.7 ± 7.3 vs. 70.8 ± 9.3 y), sex (97% vs. 81% women), 24-hr urine calcium at diagnosis (317 ± 75 vs. 311 ± 68 mg), presence of fragility fracture (50% vs. 59%), use of thiazide (83% vs. 78%), and use of anti-fracture pharmacotherapy (73% vs. 84%). 50 patients had adequate comparative longitudinal BMD data. A (+) BMD response was based on consistent increases in BMD and/or t-scores across all spine and hip sites, and a (-) BMD response was classified by decreased BMD and/or t-scores across all sites. For Thy+ vs. Thy- patients, there were 25% vs. 69% (+) BMD response, 38% vs. 12% (-) BMD response, 21% vs. 4% with no significant BMD response, and 17% vs. 15% with mixed BMD responses. Conclusions: In this group at high risk for future fragility fractures, much lower rates of BMD preservation was seen in the Thy+ as compared to the Thy- patients. Overall, AITD and medical thyroid disease was very common (48%) in this cohort of patients with IHC and OP. However, this high rate may be confounded by the selective nature of the specialty clinic population. Further research needs to delineate the impact of AITD and thyroid medication use on the progression and treatment of patients with IHC and OPO.