J Vet Sci.  2015 Dec;16(4):531-542. 10.4142/jvs.2015.16.4.531.

Quantitative CT assessment of bone mineral density in dogs with hyperadrenocorticism

• Lee D
• Lee Y
• Choi W
• Chang J
• Kang JH
• Na KJ
• Chang DW

• KMID: 2133637
• DOI: http://doi.org/10.4142/jvs.2015.16.4.531

Abstract

Canine hyperadrenocorticism (HAC) is one of the most common causes of general osteopenia. In this study, quantitative computed tomography (QCT) was used to compare the bone mineral densities (BMD) between 39 normal dogs and 8 dogs with HAC (6 pituitary-dependent hyperadrenocorticism [PDH]; pituitary dependent hyperadrenocorticism, 2 adrenal hyperadrenocorticism [ADH]; adrenal dependent hyperadrenocorticism) diagnosed through hormonal assay. A computed tomogaraphy scan of the 12th thoracic to 7th lumbar vertebra was performed and the region of interest was drawn in each trabecular and cortical bone. Mean Hounsfield unit values were converted to equivalent BMD with bone-density phantom by linear regression analysis. The converted mean trabecular BMDs were significantly lower than those of normal dogs. ADH dogs showed significantly lower BMDs at cortical bone than normal dogs. Mean trabecular BMDs of dogs with PDH using QCT were significantly lower than those of normal dogs, and both mean trabecular and cortical BMDs in dogs with ADH were significantly lower than those of normal dogs. Taken together, these findings indicate that QCT is useful to assess BMD in dogs with HAC.

Keyword

bone mineral density; dog; hyperadrenocorticism; quantitative computed tomography

MeSH Terms

Adrenocortical Hyperfunction*
Animals
Bone Density*
Bone Diseases, Metabolic
Dogs*
Linear Models
Spine

Figure

• 

  Fig. 1 Region of interest (ROI) selection for measuring Hounsfield units (HU) value at both trabecular bone (A) and cortical bone (B) of the 12th thoracic to 7th lumbar vertebra. An elliptical and manual trace of ROI that consisted exclusively of trabecular and cortical bone of the vertebral body, respectively, were drawn.

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  Fig. 2 The method of conversion of the Hounsfield units (HU) value to bone mineral density (BMD). Phantoms that contain known concentrations of calcium hydroxyapatite (from left to right 50, 100, 150 mg/cm3) were scanned with the same CT scan parameters (A). The mean and standard deviation of the HU values in ROI were measured within each calibration phantom image, after which measurements of the HU values were transformed into calcium hydroxyapatite concentration (mg/cm3) using the corresponding slope and the linear regression line (B).

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  Fig. 3 Comparison of bone mineral density between normal and HAC dogs at trabecular and cortical bone. Box-and-whisker plots show significantly lower tBMDs of HAC patients than those of normal dogs (A). Significant differences were only observed in T13, L1, L2 L4, L5, and L6. The central boxes represent values from the lower to upper quartile (25th to 75th percentile). The middle line represents the median. Significant differences were determined by a t-test. *p < 0.05, **p < 0.01, ***p < 0.001.

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  Fig. 4 Comparison of bone mineral density among each group with the same ages. Box-and-whisker plots show significantly lower tBMDs of hyperadrenocorticism (HAC) patients than those of normal dogs (A). There was no significant difference between the cBMD of normal and pituitary dependent hyperadrenocorticism (PDH) patients (B). However adrenal dependent hyperadrenocorticism (ADH) patients showed significantly lower cBMD values than normal patients. The central boxes represent values from the lower to the upper quartile (25th to 75th percentile). The middle line represents the median. Significant differences were determined by one way ANOVA. *p < 0.05, **p < 0.01, ***p < 0.001.

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  Fig. 5 Relationship between characteristics of cortisol concentration and bone mineral density at L2 and L5 among HAC dogs. Both L2 and L5 were selected as anatomical sites because they showed higher significant differences than any other sites. There were negative associations between cortisol concentration and bone mineral density of both trabecular and cortical bone at L2 and L5. Significant differences were determined by a t-test.

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  Fig. 6 Relationship between trabecular bone mineral densities (tBMDs) and chronological age among normal, PDH, and ADH patients at each vertebra. Predicted linear regression lines were developed and plotted along with scatter from actual data of tBMDs. The tBMDs-to age relationship was significant (R2 = 0.02-0.3, p < 0.01-0.001). The statistically negative correlation between trabecular bone mineral density and age was confirmed. In addition, scatterplots showed that the tBMDs of HAC patients were lower than those of normal patients.

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  Fig. 7 Relationship between cortical bone mineral densities (cBMDs) and chronological age among normal, PDH, and ADH patients at each vertebra. Predicted linear regression lines were developed and plotted along with scatter from actual data of cBMDs. The cBMDs-to age relationship was significant (R2 = 0.02-0.12, p < 0.01-0.001). The statistically negative correlation between cortical bone mineral density and age was confirmed. Scatterplots also show that cBMDs of PDH patients were not significantly different from cBMDs of normal patients. However cBMDs of ADH patients are definitely different from those of normal patients.

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  Fig. 8 The percentage of trabecular bone mineral densities (tBMD) of HAC dogs compared with those of normal dogs. Linear regression equations obtained from scatter plots of normal BMDs were used to see if BMDs of HAC dogs were actually lower than those of normal dogs at the same ages, assuming normal values are 100%. The predicted age-adjusted tBMDs of PDH and ADH dogs were approximately 20% and 40% less than those of normal patients at each vertebra, respectively.

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  Fig. 9 The percentage of cortical bone mineral densities (cBMDs) of HAC dogs compared with that of normal dogs. Linear regression equations obtained from scatter plots of normal BMDs were used to see if BMDs of HAC dogs were actually lower than those of normal dogs at the same ages, assuming normal values are 100%. The predicted age-adjusted cBMDs of PDH patients were about 10% reduced and rather to be increased at L6 vertebra. However, the cBMDs of ADH patients were approximately 60% lower than those of normal dogs, and the difference between ADH and PDH patients at this site was quite evident.

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