Bone Mineral Density Measurement at Both Spine and Hip for Diagnosing Osteoporosis in Japanese Patients

Abstract

In Japan, spinal dual-energy X-ray absorptiometry (DXA) has been commonly performed for diagnosing osteoporosis but scanning the proximal femur is not done widely. The latest Japanese guidelines for prevention and treatment of osteoporosis, revised in 2006, recommend bone mineral density (BMD) measurement at both spine and hip for diagnosing osteoporosis, although there have been no reports that proved the necessity of those measurements. One thousand forty-one women and 485 men with clinical suspicion of osteoporosis were enrolled in this study, and DXA was performed at both spine and hip. The proportions of the patients who had inconsistency between diagnosis of osteoporosis from spinal DXA and that of hip were estimated. As a result, 22% of women and 15% of men had an inconsistency with the diagnosis of osteoporosis using DXA at each measurement site. There was inconsistency in diagnosing osteoporosis using DXA at the spine and proximal femur measurement sites. Because spine and femoral DXA measurements complement each other in the diagnosis of osteoporosis, BMD measurement at both spine and hip should be performed for all Japanese patients who are suspected osteoporosis, regardless of age and sex.

Introduction

There is a close relationship between declining bone mass and increasing fracture risk. The diagnostic criteria for osteoporosis proposed by the World Health Organization (WHO) in 1994 was based on the correlation between bone mineral density (BMD) and remaining lifetime risk of fracture in a cohort of postmenopausal women. The WHO working group developed an operational definition for osteoporosis that was based on BMD. The specific BMD-based cut-off was determined to be at or below −2.5 standard deviation (SD) of young adult mean (YAM). WHO did not, however, determine specific skeletal sites for BMD measurement (1).

No consensus has been reached regarding which skeletal site/sites should be measured for diagnosing osteoporosis or estimating fracture risk. In Europe and North America, BMD measurement at hip has been regarded as important, because hip fracture, which is a typical fragility fracture, is frequent in Caucasians. The European Foundation for Osteoporosis (EFFO), which is now known as International Osteoporosis Foundation (IOF), and The National Osteoporosis Foundation (NOF) suggested measuring only the hip for the elderly for diagnosing osteoporosis 2, 3. This suggestion was based on cost-effectiveness analysis by NOF.

On the other hand, the Japanese Society for Bone and Mineral Research (JSBMR) presented the Japanese own criteria in 1996, and recommended the spine as the primary skeletal site to measure BMD (4), and hence femoral BMD often has not been used for diagnosis of osteoporosis. One of the reasons for measuring spinal BMD is that vertebral compression fractures are often symptomatic and necessary to treat in Japan, as compared with Europe and North America (5).

The International Society for Clinical Densitometry (ISCD) and the North American Menopause Society (NAMS) proposed the measurement of BMD at both spine and hip for all patients with suspicion of osteoporosis 6, 7. Some authors reported that the correlation between BMD at spine and hip was significant, but it was not sufficient to predict the other site BMD (r: 0.4–0.6) in Caucasians 8, 9, 10, 11. O'Gradaigh et al suggested in their prospective study that BMD measurement at both spine and hip should be performed to estimate one's fracture risk (12).

As the number of hip fractures in the elderly increases in Japan, because of the rapid increase of the elderly population (13), it has become more important to prevent hip fracture. Femoral BMD best predicts the risk of hip fracture 14, 15, 16, 17, and, thus, it may be important to detect persons with low femoral BMD properly and treat them suitably. The latest Japanese guidelines for prevention and treatment of osteoporosis, revised in 2006, recommended BMD measurement at both spine and hip for diagnosing osteoporosis (18), although there have been no reports which proved the necessity of BMD measurement at both spine and hip in Japanese women and men.

Having speculated that there is often discordance between spinal and femoral BMD in Japanese patients, we have measured BMD using dual-energy X-ray absorptiometry (DXA) at both spine and hip for all patients with suspected bone loss since 2003. Furthermore, we thought it was difficult in clinical practice to judge whether the measurement of femoral BMD was necessary for diagnosing osteoporosis, based on a patient's age or sex. In this prospective study, we investigated discordance in diagnosis of osteoporosis using spinal BMD and femoral BMD data from Suwa Red Cross hospital. The objective of this study was to assess the importance of BMD measurement at both spine and hip to diagnose osteoporosis in Japan.