Bone mineral assessment by dual energy X-ray absorptiometry in children with inflammatory bowel disease: evaluation by age or bone area.

Abstract

Abnormal linear growth and deficient bone mineral acquisition may coexist in children with inflammatory bowel disease (IBD). Traditionally, bone mineral assessment by dual energy x-ray absorptiometry (DXA) involves comparison to age- and gender-matched reference ranges, and these studies in children with IBD show a high prevalence of osteopenia. To compare the prevalence of osteopenia using two methods of interpretation; one adjusted for age and gender and the other adjusted for bone size and gender. Forty-seven patients with Crohn disease (CD) and 26 patients with ulcerative colitis (UC) with a median age of 13.5 years (range, 5.5-18.2 years) were evaluated. Lumbar spine (LS) and total body (TB) bone mineral content (BMC) were measured by DXA and converted to bone mineral density (BMD, g/cm) corresponding to BMC divided by the bone area. Age and gender-matched BMD standard deviation scores (SDS) were based on reference data providing age- and gender-matched BMC and bone area. These data also allowed calculation of percentage of predicted bone area for age and gender (ppBone Area) and percentage of predicted BMC for Bone Area (ppBMC). Patients with CD were shorter than those with UC (median height, SDS, -0.9 v 0, P < 0.05). Median ppBone Area for LS and TB for the whole group was 85% (10th centile, 68; 90th centile 99) and 81% (10th centile 66; 90th centile, 97), respectively. The ppBone Area at both sites was directly related to height SDS and BMI SDS (r > 0.5; P < 0.005). Median BMD SDS for LS and TB was -1.6 (10th centile -3.6; 90th centile, -0.2) and -0.9 (10th centile, -2.4; 90th centile, 0.4), respectively. Median ppBMC for LS and TB was 98% (10th centile, 84%; 90th centile, 113%) and 101% (10th centile 94%; 90th centile, 107%), respectively. The ppBMC showed no relationship to ppBone Area (r = 0.1, NS). Failure to account for bone area led to a label of moderate or severe osteopenia in 65% of cases. After adjustment for bone area, the proportion of children with osteopenia fell to 22%. The data suggest that children with IBD often have small bones for age because they have growth retardation. When DXA data are interpreted with adjustment for bone size, most children were found to have adequate bone mass. Correct interpretation of DXA is important for identifying children who may be at a real risk of osteoporosis.