Forecasting Changes in Bone Density in Boys with AN

For girls with anorexia nervosa (AN), low bone mineral density (BMD) is associated with decreased levels of bone turnover markers, in contrast to adults with AN. Although AN is mostly reported among females, it is being increasingly recognized in males—yet, according to Madhusmita Misra and colleagues at Massachusetts General Hospital and Harvard Medical School, there have been no controlled studies assessing BMD and bone turnover markers in boys with AN (J Clin Endocrinol Metab 2008; 93:3029). These researchers have shown that bone turnover markers (both for bone formation and bone resorption) are decreased in boys with AN compared to controls.

The authors note that although dual-energy x-ray absorptiometry (DEXA) is the most common tool used to measure BMD, problems can occur in younger patients with AN because it measures areal rather than true or volumetric BMD, and thus underestimates BMD in shorter children and overestimates it in taller children. Because there is a high prevalence of short stature boys with AN, the authors advise using height-adjusted measures such as lumbar spine bone mineral apparent density (BMAD), and whole body bone mineral content (WB- BMC) adjusted for height.

In addition to hormonal changes, adolescence is characterized by changes in body composition and boys particularly have marked increases in lean mass, a consistent predictor of BMD, probably due to biomechanical forces exerted by the pull of muscle on growing bone.

BMD was lower among boys with AN than the controls

Boys with AN had lower BMD and corresponding Z-scores at the spine, hip, femoral neck, trochanter, intertrochanteric region, and whole body, compared with the controls. Height-adjusted measures were also lower among those with AN. Bone formation and resorption markers were reduced in the boys with AN, indicating decreased bone turnover. Testosterone and lean mass predicted BMD. Boys with AN had lower testicular volume than did controls and lower levels of testosterone and estradiol.

Thus, just as in girls with AN, in this study boys with AN had lower than normal BMD at multiple sites, associated with deceased bone turnover markers. The impact of AN is even more marked because this occurs at the very time when bone mass accrual is critical for attaining peak bone mass.