Trabecular bone remodeling and bone balance in hyperthyroidism

In vivo tetracycline double-labeled iliac crest bone biopsies from 15 hyperthyroid patients were used for the reconstruction of curves describing the variation of resorption depth and formation thickness with time. The curves emerging were compared to curves reconstructed from 13 age- and sex-matched normal individuals (mean age 44 years). The median function period for resorptive cells in hyperthyroid patients (16 days) was about one-third the resorptive period in normals (51 days). No significant difference between the osteoclast-, mononuclear-, or preosteoblast-like cell resorption depths could be demonstrated between the two groups. Consequently, the median resorption rate in hyperthyroid patients (3.8 μm/day) was more than 3 times higher than the value in the control group (1.1 μm/day). Median Sigma_f, was shorter in the hyperthyroid group (109 days) than in the control group (151 days, P < 0.05), as was the median initial mineralization lag time (5 and 16 days, respectively, P < 0.01). No significant difference between the measured mean completed wall thickness (mcwT) values in the hyperthyroid groups and the control group could be demonstrated (58.1 and 60.5 μm respectively). Median initial mineralization rate in the hyperthyroid group (1.2 μm³/μm² per day) was not significantly higher than the value calculated in the control group (0.9 μm³/ μm² per day), but median initial matrix appositional rate in hyperthyroids (4.8 μm³/μm² per day) was 3 times higher than the value calculated for normals (1.6 μm³/μm² per day) (P < 0.01). Direct measurements of mean completed wall thickness in the hyperthyroid group gave results (58.1 μm) that were not in accordance with the mean completed wall thickness calculated from the growth curve (52.1 μm, P < 0.02). In normals no such discrepancy could be demonstrated. Using the mcwT value estimated from the growth curve, the bone formation period was calculated to 90 days for hyperthyroid patients. This maximal estimate for mcwT was also significantly lower than the mean resorption depth measured in the hyperthyroid group (61.7 μm, P < 0.05), which means that a net negative balance per remodeling cycle existed in the hyperthyroid group. Bone balance was preserved in the control group.