"Bone density analysis using dual energy x-ray (DXA) bone absorptiometry in clinical investigation CEPEM Centro de Estudos e Pesquisas da Mulher - Rio de Janeiro – Brasil C.T.C,Maksoud,C.T.M,Iruzun,C,Carvão

INTRODUCTION Osteoporosis is a disease that compromises the bony architecture making it fragile and prone to fractures with the reduction of the bone mineral density (BMD). The loss of bone mass may be associated to specific pathologies and to the development of natural ageing; however it may be stressed by nutritional deficiencies, deficit of estrogens in post menopausal women, use of corticoids or even be related to pubertal nutritional alterations or delays that might hinder the development of the peak bone mass.

Osteoporosis may be asymptomatic until fracture occurs. The most frequent fractures compromise the hips and spine, determining difficulties in locomotion, chronic pain, deformities and the development of comorbidities, which might lead to leaving an unproductive being or even to death.

For the diagnosis of osteoporosis and the monitoring of the variables of BMD along time and dual-energy X-ray absorptiometry (DXA) a golden-standard quantitative, non-invasive technique. It uses two different radiation energy intensities, which allows distinguishing the attenuation profiles thus contrasting soft tissue and bone. The dosage of radiation used in the attainment of studies in skeletal sites is considered very low and without relevant biological effect. The BMD measurements are used in conjunction with clinical data for the prediction of the risk of fractures.

Table 1: DXA measurements of menopausal women by age groups (n=335) n (%) 40-50 35 (10) 51-60 156 (47) Age groups 61-70 91 (27) 71-80 45 (14) >=81 8 (2) total 335 (100) Lumbar Spine BMD (g/cm 2 ) mean(SD) median T score mean(SD) median -0.4 (1.4) -0.1

-0.8 (1.2) -1.1

-0.9 (1.3) -0.9

-1.1 (1.5) -1.9

-0.9 (1.5) -0.8

1.076 (0.159) 1.058

-0.8 (1.3) -1.0

Femoral neck BMD (g/cm 2 ) mean(SD) median T score mean(SD) median -0.6 (1.0) -0.6

-1.0 (0.8) -1.1

-1.1 (0.8) -1.2

-1.7 (0.8) -1.8

-1.9 (0.8) -1.9

0.877 (0.122) 0.873

-1.1 (0.9) -1.2

Total Hip BMD (g/cm 2 ) mean(SD) median T score mean(SD) median -0.4 (1.0) -0.2

-0.6 (0.9) -0.7

-0.7 (1.0) -0.8

-1.3 (1.0) -1.2

-1.5 (1.1) -1.2

0.912 (0.161) 0.911

-0.7 (1.0) -0.8

Table 2: DXA measurements of premenopausal women by age groups (n=73) Age Groups n (%) <40 10 (14) 41-50 55 (75) 51-60 8 (11) total 73 Lumbar Spine BMD (g/cm 2 ) mean(SD) median Z score mean(SD) median -0.3(1.0) -0.3

Femoral neck BMD (g/cm 2 ) mean(SD) median Z score mean(SD) median -0.7(0.5) -0.8

Total Hip BMD (g/cm 2 mean(SD) median Z score mean(SD) median -0.6(0.8) -0.5

0.3(1.1) 0.2

0.8(1.1) 1.0

-0.3(0.8) 0.0

0.6(1.3) 1.0

0.1(0.9) 0.1

0.8(1.0) 0.7

1.200 (0.148) 1197 0.3(1.2) 0.2

0.961 (0.123) 0.963

-0.5(0.9) -0.1

0.994 (0.133) 1.001

0.1(0.9) 0.1

MATERIALS AND METHODS The criteria for gauging, positioning and the variable coefficient are in accordance with the patterns determined by the Programa de Controle de Qualidade da Sociedade Brasileira de Densitometria Clínica (ProQuad-SBDens) affiliate with the International Society for Clinical Densitometry (ISCD). Baseline density measurements for the lumbar spine (L1-L4) and for proximal femur (hip) were performed with dual-energy X-ray absorptiometry Lunar DPX NT in patients referred to diagnostic evaluation of bone mass. The measurement of bone mass by DXA is expressed in g/cm² because it is a measure of area. We summarized the bone mineral density (BMD) of lumbar spine, femoral neck and total hip, with T scores and Z-scores. The cutoffs for osteoporosis were based on the WHO international standard.

In figure 1, we can observe a greater extent in the values of lumbar spine T score in all age groups as well as an evident downfall in the femoral neck T score with the advancing age compared to the T score in other sites.

The difference between means of BMD lumbar spine and femoral neck for postmenopausal and premenopausal women was statistically significant (p<0.000). However, the difference between the means of BMD femoral neck age groups was statistically significant but between the means of BMD spine was not (p=0.1750).

In figure 2, we can observe that as age progresses the Z scores of all sites also do so.

Figure 1: Distribution of T scores according to skeletal site by age group in postmenopausal women (n=335).

Figure 2: Distribution of Z scores according skeletal site by age group in premenopausal women (n=73).

RESULTS The studied group was composed of 335 postmenopausal women with the average age of 63 (SD=10) varying from 43 to 83 years of age and 73 premenopausal women with the average age of 46 (SD=4) varying from 30 to 53 years of age.

The prevalence risk factor was of 13.2% for cigarette smoking, 10.2% for fracture family history, and 16.9% for previous fracture analysis. The difference among the mean values of BMD in the lumbar spine with and without previous history of fractures achieved statistical significance (p<0.05). The lowest means of BMD related to other risk factors such as smoking and family history of fractures did not achieve statistical significance.

The values obtained from BMD in the subgroup of menopausal women with the according T scores per age group can be viewed on table 1. Osteoporosis was diagnosed in 15% of the women (n = 50) considering the two skeletal sites and selecting the lowest T score whereas osteopenia was found in 68% (n =229).

Considering lumbar spine and femoral neck T-score for the diagnosis of normal, osteopenia and osteoporosis the agreement was of 65%.

When considering the femoral site as a gold standard, osteoporosis and osteopenia are underestimated by 21%. The prevalence of osteoporosis was higher in the group of postmenopausal women over 70 years of age (55%).

In the subgroup of premenopausal women (n=73), the values obtained for BMD and the according Z scores for age group can be viewed on table 2. In 17% of the cases of premenopausal women (n = 73) bone mineral densities were found less than the expected for the age. DISCUSSION The presence of family history of fractures was associated to lower values of BMD for the lumbar spine.

Osteoporosis was best identified considering BMD of the femoral neck mainly for patients older than 73 years of age. .

In the older group, the femoral neck evaluation was more confident than the lumbar spine probably because it was less compromised by lumbar spine degenerative changes that might overestimate the BMD.

The lowest Z scores were observed in younger women and they correspond to the lowest values of BMI by age group.

This behavior may be related to deficiencies in the development of peak bone mass. However, follow-up studies with an amplified analysis of this age group are necessary for a better representation of these findings.

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Table 2: DXA measurements of premenopausal women by age groups (n=73) Age Groups n (%) <40 10 (14) 41-50 55 (75) 51-60 8 (11) total 73 Lumbar Spine BMD (g/cm 2 ) mean(SD) median Z score mean(SD) median -0.3(1.0) -0.3

Femoral neck BMD (g/cm 2 ) mean(SD) median Z score mean(SD) median -0.7(0.5) -0.8

Total Hip BMD (g/cm 2 ) mean(SD) median Z score mean(SD) median -0.6(0.8) -0.5

0.3(1.1) 0.2

-0.3(0.8) 0.0

0.1(0.9) 0.1

0.8(1.1) 1.0

0.6(1.3) 1.0

0.8(1.0) 0.7

1.200 (0.148) 1197 0.3(1.2) 0.2

0.961 (0.123) 0.963

-0.5(0.9) -0.1

0.994 (0.133) 1.001

0.1(0.9) 0.1

Table 1: DXA measurements of menopausal women by age groups (n=335) Age groups n (%) 40-50 35 (10) 51-60 156 (47) 61-70 91 (27) 71-80 45 (14) >=81 8 (2) total 335 (100) Lumbar Spine BMD (g/cm 2 ) mean(SD) median T score mean(SD) median -0.4 (1.4) -0.1

-0.8 (1.2) -1.1

-0.9 (1.3) -0.9

-1.1 (1.5) -1.9

-0.9 (1.5) -0.8

1.076 (0.159) 1.058

-0.8 (1.3) -1.0

Femoral neck BMD (g/cm 2 ) mean(SD) median T score mean(SD) median -0.6 (1.0) -0.6

-1.0 (0.8) -1.1

-1.1 (0.8) -1.2

-1.7 (0.8) -1.8

-1.9 (0.8) -1.9

0.877 (0.122) 0.873

-1.1 (0.9) -1.2

Total Hip BMD (g/cm 2 ) mean(SD) median T score mean(SD) median -0.4 (1.0) -0.2

-0.6 (0.9) -0.7

-0.7 (1.0) -0.8

-1.3 (1.0) -1.2

-1.5 (1.1) -1.2

0.912 (0.161) 0.911

-0.7 (1.0) -0.8