Changes in the mineral composition of orbital bones in thyroid disease

Thyroid diseases lead to significant systemic changes in bone tissue, but analysis and densitometric assessment in this pathology is usually limited to the lumbar vertebrae and the femoral and radial bones. At the same time, there are grounds to assume presence of significant changes in other bony structures, primarily the orbit. To date, no data are available on specific changes in the mineral composition of orbital bones in thyroid pathology. Objective. This study assessed the mineral composition of the bone tissue of the lateral orbital wall in thyroid eye disease (TED) using scanning electron microscopy with energy dispersive analysis. Material and methods. The study examined samples of the greater wing of the sphenoid bone (GWS) obtained during deep lateral orbital decompression in 33 patients with TED (30—59 years, group 1) and 25 cadaveric sphenoid bone samples from patients of a comparable age range (group 2). Based on the results of semiquantitative chemical microanalysis, we calculated the number of Na+, Ca2+, and Mg2+ cations per hydroxyapatite formula unit and assessed the overall mineralization of the samples. Results. In patients with TED aged 30—44 years, the content of Mg2+ cations in the hydroxyapatite of the GWS was significantly lower than in the control group (p<0.05) (0.16 vs 0.19 f.u.). At the same time, in both groups, the content of Mg2+ cations in bone tissue hydroxyapatite increased with age (p<0.05; r=0.37 and r=0.43 for groups 1 and 2, respectively), whereas overall mineralization decreased, which is consistent with the general concepts of age-related changes in bone mineral. Conclusion. The identified differences indicate two mechanisms of bone tissue changes: hypermagnesemic (age-related) and hypomagnesemic (associated with thyroid hyperfunction). This concept may provide a basis for personalized strategies to correct mineral metabolism based on the patient’s somatic status.