Three-Year Changes in Bone Mineral Mass of Postmenopausal Osteoporotic Patients Based on Neutron Activation Analysis of the Central Third of the Skeleton*

Abstract

Thirty-two patients with postmenopausal osteoporosis have been followed for periods of 3 yr or more to assess the effects of treatment on bone mineral mass based on sequential measurements of bone mineral in the central third of the skeleton. Neutron activation analysis (NAA) was used to measure calcium in the trunk and proximal femurs. The NAA measurement is expressed as an index, CaBI, which relates the subject's Ca value to the estimated mean value for normal subjects of the same size based on height and arm span. Bone and serum fluoride concentrations were measured, and bone biopsies were carried out in many cases. The treatments consisted of various combinations of NaF (25 mg, twice daily), calcium (1 g/day), vitamin D₂ (50,000 IU twice weekly), and estrogen (0.625 mg/day). NaF was always given in combination with Ca and vitamin D_2. During the 3-yr treatment period, the 32 patients showed changes in bone mineral mass from losses of −10.5% to increases of 21%. The coefficient of variation of 9% for changes in CaBI is significantly greater (P < 0.01, by the F test) than that of 1.7% for volunteers followed over the same period of time. The 14 patients treated without NaF showed a mean (± SE) increase in CaBI of 3.5 ± 0.5%. Patients treated with NaF had variable results. The variations were attributed, at least in part, to the amount of F retained in the bone. The 8 patients with evidence of adequate F retention (bone F/Ca concentrations more than 10.8 mg/g and/or serum F more than 5 /xmol/liter) had a mean (± SE) increase in CaBI of 12.7 ± 2.3%, which is significantly greater (P < 0.01, by Welch test) than the mean change for controls. The 5 patients with evidence of inadequate F retention had a mean (± SE) loss in CaBI of −7.2 ± 1.0%. With NaF treatment, the increase in bone mineral mass (CaBI) was associated with histological evidence of fluorosis (increased percentages of formation and resorption surfaces, increased osteoid index, and thick osteoid seams). With adequate F therapy, significant increases in CaBI are consistent with reported data on iliac bone biopsies and spinal radiology but differ from results by densitometry of the forearm or by total body neutron activation analysis. These findings emphasize the importance of measuring skeletal changes in the central rather than the peripheral skeleton when monitoring osteoporotic patients.