Interpretation of bone mineral density values in pediatric Crohn's disease

Patients with Crohn's disease (CD) often have low bone mineral density (BMD) for their chronological age (CA). However, pediatric cases frequently have growth failure and delayed bone age (BA) and height age (HA). Do they really have the amount of osteoporosis as measured by BMD and calculated for their CA? The aim was to compare z-scores for BMD in relation to CA and z-scores corrected for BA or height age in pediatric patients. A group of 43 pediatric patients (mean age, 12 years; 14 girls, 29 boys) with CD in remission, prospectively had BMD (measured by dual energy x-ray absorptiometry) and BA. Abnormally low z-score for BMD (below 2 standard deviation [SD] for CA was found in 19 patients (44%). Among these, 9 patients (21% overall) had a BA of more than 2 SD lower than their CA and 12 had height age at least 2 years below CA. When the BMD z-score in these patients was corrected for their BA and height age, 6 of 9 and 8 of 12 patients had a normal BMD. In conclusion, when corrected for BA or CA delay, BMD was abnormal in 26 to 30% rather than 44% of cases. Correct assessment of BMD in Crohn's disease patients with bone age delay requires interpretation in terms of BA or HA, rather than CA.