Dynamic and structural properties of the skeleton in hypoparathyroidism

Abstract

Hypoparathyroidism, a disorder in which PTH is absent, is associated with BMD that is above average. We studied associated structural and dynamic properties of the skeleton in hypoparathyroidism. Thirty-three subjects with hypoparathyroidism and 33 age- and sex-matched control subjects with no known metabolic diseases underwent percutaneous iliac crest bone biopsies after double-labeling with tetracycline. The main outcome was histomorphometric assessment of structural and dynamic skeletal parameters. Subjects with hypoparathyroidism had greater cancellous bone volume (mean +/- SD; BV/TV: 23.5 +/- 8 versus 19.7 +/- 5%, p = 0.02), trabecular width (Tb.Wi: 136.1 +/- 37 versus 119.3 +/- 21 microm, p = 0.03), and cortical width (Ct.Wi: 923.4 +/- 420 versus 753.5 +/- 246 microm, p = 0.05) than control subjects. Dynamic skeletal indices, including mineralizing surface (MS: 0.85 +/- 1.58 versus 4.27 +/- 3.32%, p < 0.0001) and bone formation rate (BFR/BS: 0.006 +/- 0.014 versus 0.032 +/- 0.028 microm(3)/microm(2)/d, p < 0.0001), were profoundly suppressed in the hypoparathyroid subjects. We conclude that hypoparathyroidism is characterized by markedly unusual structural and dynamic properties of bone.

FIG. 1

Bone densitometry in hypoparathyroidism. Z-scores are used because of the wide age distribution of the patients. Four different sites (lumbar spine, total hip, femoral neck, and distal one-third radius) are shown (mean ± SD). Although BMD data are not available for the age-matched controls, mean BMD in the hypoparathyroid subjects is relatively well maintained at all sites.

FIG. 2

A representative photomicrograph of a biopsy from a hypoparathyroid subject (right) compared with a normal control (left). The hypoparathyroid subject is a 32-yr-old premenopausal woman; the control is a 22-yr-old premenopausal woman. In the hypoparathyroid subject, BV/TV was 26% and Ct.Wi was 890 μm, whereas in the control subject, BV/TV was 21% and Ct.Wi was 590 μm. More bone is present in both the cancellous and cortical compartments in the hypoparathyroid subject.

FIG. 3

Reduced tetracycline uptake in a hypoparathyroid bone biopsy (right) compared with a control (left). The hypoparathyroid subject is a 61-yr-old postmenopausal woman; the control is a 63-yr-old postmenopausal woman. Double labels are visualized in the normal subject (arrow), whereas in the hypoparathyroid subject, virtually no uptake of tetracycline is detected (arrow), indicating that bone formation is markedly reduced.