Discrepancy in results between spine and hip scans of a woman with end stage renal disease

Vertebral Bone Density Measurements by DXA are Influenced by Hepatic Iron Overload in Patients with Hemoglobinopathies

Interference from metal hardware (piercings; buttons on clothing; and ingested material, e.g. barium) is well documented in bone health assessments by dual-energy X-ray absorptiometry (DXA). It is unknown if iron in hepatic tissue of highly iron-loaded patients could be mistakenly assessed by DXA as bone, and if this would lead to increased areal bone mineral density (aBMD) lumbar spine Z-scores derived by DXA. Our hypothesis is that iron in the liver of heavily loaded patients will artificially raise aBMD in the spine, and thereby lead to an error in the DXA scan. This study consisted of a retrospective chart review and re-analysis of DXA scans from patients with sickle cell disease and thalassemia combined with prospective DXA and liver iron concentration (LIC) measurements from healthy controls. Patients who previously had both a DXA and LIC measurement were compared with controls. aBMD of individual vertebrae were analyzed and grouped by those that may be covered by the liver (L1 or L1/2) with those typically not (L3/4). Subjects were grouped by diagnosis and LIC severity. Phantoms were created to mimic the geometry of iron loaded liver tissue, and analyzed by DXA. A significant effect was observed in the difference of BMD Z-score of L1 and L 3/4 when patients with LIC < 1000 were compared to those with >5000 µg Fe/g wet tissue (p = 0.043). A significant relationship was also observed in the difference in aBMD Z-score of L1 and 3/4 when controls were compared to the high iron group (p = 0.037). These findings were supported by phantom experiments. These results suggest that there is a relationship between hepatic iron and increased L1 aBMD Z-scores in highly iron-loaded patients. Given patients with hemoglobinopathies are at increased risk for osteoporosis, clinicians should maintain a higher index of suspicion when diagnosing low bone mass.

Management of osteoporosis in CKD Stages 3 to 5

Osteoporosis and chronic kidney disease (CKD) are both common conditions of older adults and both may be associated with substantial morbidity. However, biochemical and histologic changes that occur with progressive kidney disease require specific interventions, some of which may be concordant with osteoporosis management in the general population, whereas others may be less relevant or perhaps even harmful. In this article, we review the diagnosis of and management strategies for osteoporosis in individuals with CKD, placing these into perspective with the recently published KDIGO (Kidney Disease: Improving Global Outcomes) guidelines for treatment of CKD-mineral and bone disorder (CKD-MBD). Specifically, we highlight osteoporosis treatment recommendations by CKD stage and discuss new avenues for osteoporosis treatment that may be useful in individuals with CKD.

The effect of common artifacts lateral to the spine on bone mineral density in the lumbar spine

Artifacts such as surgical clips, gallstones, and kidney stones are often present in the soft tissue stripe lateral to vertebral bodies. Using cadaveric specimens, we placed bra wires, gallbladder clips, a large gallstone, a calcium carbonate or a calcium citrate pill lateral to L1, or a large or small calcium-containing kidney stone lateral to L3 and compared the mean bone mineral density (BMD) of individual vertebral bodies and L1-L4 with and without the soft tissue artifact. The specimens used had high BMD (L1-L4 BMD=1.049 g/cm2) and low BMD (L1-L4 BMD=0.669 g/cm2) and were scanned with a Hologic Discovery W scanner with 12.7 software in the array mode. None of the artifacts affected L1 or L3 BMD or L1-L4 BMD significantly in the high BMD spine. However, bra wires, a large calcium citrate pill lateral to L1, 3 calcium citrate pills lateral to L1, a calcium carbonate pill over L1, and 3 calcium carbonate pills lateral to L1 did affect L1-L4 BMD in low BMD torso. Gallbladder clips or gallstone did not affect L1-L4 BMD in either specimen. We conclude that artifacts lateral to the spine, particularly in a low BMD spine, can affect the interpretation of L1-L4 BMD using a Hologic Discovery W scanner with 12.7 software in array mode.

Black hole artifacts-a new potential pitfall for DXA accuracy?

Certain types of metallic objects apparently have high attenuation (a white image) on dual-energy X-ray absorptiometry (DXA) scan images, but instead show up as black (black hole artifacts). When small, these artifacts may easily be missed on visual inspection. We hypothesized that such "black hole" artifacts could have a significant effect on bone mineral density (BMD) results. Human use approval (Institutional Review Board [IRB]) was obtained to publish patient scans and an IRB waiver was obtained for nonhuman research. We placed individual surgical clips and cassettes of clips of tantalum, stainless steel and titanium, and a bullet over the third lumbar vertebra (L3) of a Hologic spine phantom. In addition, 4 or 8 individual tantalum or stainless steel clips and tantalum squares were placed over L3 of cadaveric spines (high-density spine L1-L4 BMD=1.049 g/cm2) and low-density spine BMD (L1-L4 BMD=0.669 g/cm2) with attached soft tissues. Stainless steel and titanium clips scanned as white objects with DXA. A bullet and tantalum clips scanned black (black holes). All clip types were visible on single-energy scans as white objects. Eight tantalum clips significantly lowered L3 BMD compared to 4 or 0 clips in the high-density spine. There were no significant differences in BMD L1-L4 between 0, 4, and 8 tantalum clips in the high-density spine. In the low-density spine, 8 tantalum clips over L3 had significantly lower BMD compared to 4 tantalum clips overlying L3 and 4 clips lateral to L3 and 4 clips over L3. All of these scenarios had lower L3 BMD than no tantalum clips overlying L3. The BMD of L1-L4 was lowest with 8 clips at L3, but was not significantly different than no clips overlying L3. Eight tantalum clips lateral to L3 was significantly higher than no clips over L3. Black hole artifacts can occur in DXA scans containing certain metals like tantalum surgical clips. Although these surgical clips could decrease BMD at a localized area, they do not significantly decrease the L1-L4 spine BMD in a high-density spine specimen. In a low-density spine specimen, tantalum clips do have the potential to alter BMD of a single vertebral body and L1-L4. Attention should be paid to the possibility of black hole artifacts on DXA scans and the effect they may have on spine results. Viewing scans in the single-energy mode can be used to verify the presence of tantalum clips.

Soft tissue density variations in thalassemia major: a possible pitfall in lumbar bone mineral density measurements by dual-energy X-ray absorptiometry

Osteoporosis is common in patients with thalassemia major. A 16-year-old patient with thalassemia major was referred for evaluation of osteoporosis. The results of dual-energy X-ray absorptiometry in a patient with thalassemia major are presented. The patient underwent measurements of the spine in both AP and lateral position. The DXA scan of the spine in AP projection showed diffusely increased density overlying the lower thoracic and upper lumbar vertebrae. The overall density of L(2)-L(4) was 0.6465 g/cm(2) (4.93 SD as compared with young adults). The DXA scan of the spine in lateral projection showed diffusely increased density in front part of the spine. The BMD of the L(3) vertebra was 0.3669 g/cm(2) (0.30 SD as compared with young adults). It is important to interpret the images visually in order to obtain true values of BMD, and preclude invalid BMD measurements.

Effects of short-term alendronate on bone mineral density in haemodialysis patients

BACKGROUND

Low bone mineral density (BMD) is common in dialysis patients. Low BMD predicts the fracture risk in the general population. Bisphosphonate therapy improves BMD and lowers the fracture risk in many populations, but has not been tested in dialysis patients because of concerns about toxicity. In this investigation, the effect of a short course of alendronate on BMD in haemodialysis (HD) patients is evaluated.

METHODS

Thirty-one healthy HD patients were randomized to placebo versus 40 mg alendronate, taken once a week for 6 weeks. Hip and lumbar spine BMD were measured by dual energy X-ray absorptiometry at baseline and at 6 months. Osteocalcin, parathyroid hormone, calcium, phosphorous and alkaline phosphatase levels were assayed at baseline and at 1, 3 and 6 months.

RESULTS

The BMD and T-scores in specific regions of the hip were stable in the treatment group and decreased in the placebo group (P=0.05). The lumbar spine density increased minimally in both groups. In the treatment group, osteocalcin levels declined significantly at 1 month (P<0.05) and remained low. The main side-effect in the alendronate group was occurrence of gastroesophageal reflux symptoms in three subjects.

CONCLUSIONS

Low-dose alendronate, administered for a limited duration, appears to be well tolerated in dialysis patients. The BMD and T-scores declined at certain hip regions in the placebo group over 6 months, while remaining stable in the treatment group, suggesting a bone-preserving effect of alendronate. Further studies of longer duration, and including examination of bone histology, are needed to assess whether bisphosphonates can be used to preserve BMD in dialysis patients.

Risk factors for decreased total body and regional bone mineral density in hemodialysis patients with severe secondary hyperparathyroidism

Hyperparathyroidism contributes significantly to decreased bone mineral density (BMD) in end-stage renal disease patients, but this negative influence is not homogeneous throughout the skeleton. We studied the BMD by dual-energy X-ray absorptiometry on total body and on different regions of the skeleton in 42 patients with severe hyperparathyroidism on hemodialysis. We also evaluated the relationship between different risk factors and BMD found on the regions examined in these patients. The legs and other sites where cortical bone predominate were mostly affected, whereas trabecular bone was relatively preserved. This is probably the result of the different effects of hyperparathyroidism on cortical and trabecular bone, but we cannot rule out the interference of ectopic calcifications and sclerotic lesions of vertebral end-plates falsely increasing lumbar spine BMD. The main determinants of low total-body BMD were, in order of importance, immobility, high intact parathyroid hormone levels, low body mass index, and low albumin. Eleven patients presented with pathologic fractures, mainly in the legs, and BMD was lower in this group than in patients without fractures. In conclusion, our study makes clear that hyperparathyroidism is a great threat to bone density in hemodialysis patients, mainly in the legs, the site mostly affected by fragility fractures in our patients. Physicians must worry not only with high parathyroid hormone levels, but also with the nutritional state of these patients.