Bone Mineral Density in Short Individuals; How Can We Interpret It?

M Nadeem, EF Roche 

Department of Paediatrics, National Children’s Hospital, Tallaght, Dublin 24

It has been reported that short individuals are likely to be misdiagnosed with reduced bone density when areal bone mineral density or age-adjusted Z-score is used. Adjustments for body size (bone mineral apparent density) can eliminate this issue. We therefore set out to examine whether areal bone mineral density or bone mineral apparent density should be used in those with short stature.

In short individuals, areal bone mineral density (BMD) (g/cm2) can be affected by body size, therefore bone mineral apparent density (BMAD; g/cm3)] is recommended1. Using BMAD, but not BMD in short individuals, was recommended in previous studies. In those with Turner syndrome (TS), the number of women diagnosed with osteoporosis reduced from 8 to 2 using adjustments for skeletal size 1. Similarly, short adolescents born small for gestational age had reduced BMD. but normal bone size-corrected BMAD2. A high prevalence of osteopenia and osteoporosis in young adults with cystic fibrosis has been reported3. We therefore set out to examine whether BMAD should be calculated in Irish girls with short stature, such as those with TS, for example.

Of 35 girls (mean age16.7, SD 2.61 years), with genetically confirmed TS, 32 agreed to participate in the study. BMD of lumbar spine was estimated using dual-energy x-rayabsorptiometry (DXA). To correct for bone size, BMAD was measured4. Standard deviation score (SDS) was calculated. Ethical approval has been obtained from our local hospital ethics committee. Data were analysed using SPSS, version 21.0. Descriptive statistics were measured. t-Test was used to compare between means of 2 groups.

Compared with age-matched Irish general population, mean height SDS was -2.1 (p value 0.00). As it was described in this cohort of patients, over-diagnosis of low BMD can occur if BMD rather than BMAD is considered when evaluating bone density in children and adolescents with short stature such as TS. For example, mean BMD SDS was -1.53 (SD 0.70); however this was significantly lower than calculated mean BMAD SDS -0.87 (SD 0.81) (p value =0.00).

In conclusion, over-diagnosis of low BMD and age-matched Z scores in children and adolescents known to have short stature should be avoided; such as those with TS, for example. In those with short stature, low BMD should be interpreted in the context of body size and BMAD should be calculated.

 

Corresponding author: Dr Montasser Nadeem, Paediatric consultant, NCH, Tallaght, Dublin 24

Email: drnadeem.gad@gmail.com

References:

1 Bakalov VK, ChenML, Baron J, Hanton LB, Reynolds JC,Stratakis CA, et al. Bone mineral densityand fractures in Turner syndrome. Am JMed 2003;115:259-64.

2 Lem AJ1, van der Kaay DC, Hokken-Koelega AC. Bone mineral density and body composition in short children born SGA during growth hormone and gonadotropin releasing hormone analog treatment. J Clin Endocrinol Metab. 2013 Jan;98:77-86.

3 Paccou J1, Zeboulon N, Combescure C, Gossec L, Cortet B.. The prevalence of osteoporosis, osteopenia, and fractures among adults with cystic fibrosis: a systematic literature review with meta-analysis. Calcif Tissue Int. 2010 Jan;86:1-7

4 van der Sluis IM, deRidder MA, Boot AM, Krenning EP,de Muinck Keizer-Schrama SM. Reference data for bone density and body composition measured with dual energy x ray absorptiometry in white children and young adults. Arch Dis Child 2002;87:341-7; discussion341-7.

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