The basis for the post-parathyroidectomy increase in bone mass.

The bone remodeling transient is a self-limited change in measurable bone mass, detectable by dual-energy X-ray absorptiometry (DXA) or by calcium balance methods, which occurs whenever the skeleton undergoes a shift in bone remodeling activity from one steady state to another. Assessing the true effect on bone mass of therapy that alters remodeling requires both a period of observation long enough to characterize the new steady state and explicit provision for the transient. To help with such analysis, a multivariate computer model of the bone remodeling system has been developed and applied usefully to a variety of data sets describing the response to treatment. Because parathyroid hormone (PTH) is the principal determinant of the quantity of bone remodeling, it follows that efficacious treatment of hyperparathyroidism will produce a bone remodeling transient. Using published values for the level of bone remodeling activity in postmenopausal women with mild hyperparathyroidism, it can be calculated that successful treatment would produce an increase in measurable spine bone mineral density (BMD) of about 12% by 1 year after surgery. In more severe cases, with higher levels of remodeling, one-time BMD increases of more than 30% will occur. In general, it can be said that, in typical postmenopausal women, a doubling of remodeling rate in the hyperparathyroid state will, on successful treatment, produce a positive transient amounting to about 8% above the presurgery BMD level.