Discrepant Areal and Volumetric Bone Density Measurements in a Young Woman with Idiopathic Low Bone Mineral Density

Abstract

To discuss a case of idiopathic low bone density in a young woman. We present a detailed report that includes clinical, laboratory, and radiologic assessment of a pre-menopausal woman with idiopathic low bone mass. A 34-year-old healthy woman of small body habitus was found by dual-energy x-ray absorptiometry to have bone mineral density (BMD) that was less than 2.5 standard deviations below the young and age-matched norm. After a thorough evaluation, no cause of osteoporosis was identified. Calculation of bone mineral apparent density, which minimizes the effect of small skeletal size on areal BMD, resulted in only a modest improvement in T-scores. Measurement of lumbar spine volumetric BMD by quantitative computed tomography, however, revealed a significantly improved T-score of -1.6. This report highlights the complexities of low BMD measurements in otherwise healthy young women as well as the potential application of bone mineral apparent density and quantitative computed tomography in the evaluation of low BMD in young women with small skeletal frames.