Nuclear Medicine/Bone Mineral Density

Bone Mineral Density

DXA Scan

Indications

The Most Established Risk Factors for Osteoporosis

• Age greater than 65
• Gender - At the same age, females are at higher risk than males for an osteoporotic fracture in general. However, males are at higher risk for a hip fracture specifically.
• Weight and Height(BMI)
• A personal or family history of fracture from something simple like a fall or minor bump.
• Other causes such as certain drugs like steroids or chemotherapy
• Various metabolic conditions that put one at risk for low bone density:
  • Type I Diebetes
  • Long-standing untreated Hyperthyroidism
  • Hyperparathyroidism
  • Hypogonadism - high risk for males but normal if a female has had menopause after the age of 45
  • Rheumatoid arthritis
• Smoking
• Consuming >3 alcoholic beverages per day

Appropriate ordering of DXA scans

• In any patient, there are certain indications for scanning that do not require further stratification:
  • Any personal history of fragility fractures?(like a fracture from a simple bump or low-impact fall) -> Scanning is appropriate.
  • Prior scanning showing low bone density? -> Follow up scanning is appropriate.
  • Prior scanning normal but secondary causes for potential interval bone loss are significant and/or expected.

• All other patients:
  • Males
    • Low risk factors? -> Follow up visit for reevaluation only, no definite age is known for screening DXA
    • High risk factors (as above) or with clinical suspicion of low bone density -> Scanning is appropriate
  • Females
    • Greater than 65 y/o? -> Scanning is appropriate
    • Less than 65 y/o?:
      • High risk factors (as above) or with clinical suspicion of low bone density -> Scanning is appropriate.
      • Low risk factors -> Follow-up reevaluation only.

How To Read a DXA scan

Visual Analysis

• Hip
  • Attention needs to be given to anything which might alter the BMD, such as overlap of the hip with the ischium or dense foreign bodies. Anything aberrant density that exists within the background ROI or the ROI that draws the total hip or femoral neck will change bone density.
  • If a corner of the femoral neck ROI does include part of the ischium, this usually can be manually excluded by the technologist performing the exam.
  • Optimal rotation of the hip allows you to just see the lesser trochanter, which helps the computer to draw the ROIs correctly.
  • Many hips have prostheses such as a hip replacement. Obviously, this cannot be used and the other hip or the forearm should be used for analysis instead.

• Spine
  • Significant sclerosis or scolioses should be noted and likely falsely elevates the bone density in the spine. When describing these findings, try to not use clinical diagnoses such as "osteoarthritis of the spine". The correct term would be "sclerosis."
  • Compression fractures need to be described. There is some controversy about whether or not interpreting clinicians should use DXA to screen for fractures. The technique is sometimes called visual fracture analysis (VFA) and can be billed for in some cases. Please note that a compression fracture may be a sole indicator for treatment but the DXA is not a diagnostic film. Most clinicians order a diagnostic radiograph of the lumbar spine if something is concerning on the DXA.

T vs Z scores

• T-scores
  • Used for postmenopausal and perimenopausal women
  • and men ≥ 50 y/o
• Z-scores
  • Used for premenopausal women, children, and men < 50 y/o

WHO Classification

• See the table at the bottom of this page for WHO classification for postmenopausal osteoporosis

FRAX Calculation

WHO Fracture Risk (FRAX)

• WHY USE THIS?
  • Guideline for appropriate treatment
  • FRAX calculation is used to make pharmacologic treatment decisions which is defined as treatment outside of Calcium and Vitamin D supplementation such as with a bisphosphonate.
  • Calculation is applied to osteopenic (not osteoporotic) patients aged 40-90 y/o.
  • A known fragility fracture is a sole indication for treatment and should be included as a disclaimer when FRAX risk does not meet the threshold for treatment.
  • It is found that simply using a T-score in bone mineral density (BMD) has been shown to be insufficient in assessing fracture risk in patients and is not ideal as a sole indicator in guiding bone-building or bone-retaining pharmacological treatment outside of normal vitamin D and calcium supplementation. Additionally, there is a general feeling in the public and in medicine that if you have "Osteopenia" that this is an entity that requires treatment, but does not have support in the literature.
  • A study of approximately 60,000 patients (40-90 yr old men and women) was used to stratify the risk of fracture as it applied to the BMD of the femoral neck and/or various indicators in the patient's past medical history. This data was used to form a calculation tool to help guide treatment, called FRAX (Fracture Risk Assessment Tool). This tool can be found online and can give very helpful specified information with variables including race and nationality.
• A calculated 10 year FRAX risk of fracture of at least 3% at the hip, and at least 20% for a "major osteoporotic fracture," would indicate that the patient would benefit from pharmacological treatment.
• It must be noted that FRAX is not intended to be used as a sole determinant in "treat vs not treat." The consensus is that a variety of clear indications for treatment exist, that may include:
  • History of vertebral or hip fracture that is felt to be caused by low BMD.
  • A diagnosis of primary osteoporosis - This diagnosis is made only if other treatable, non-primary causes of osteoporosis have been ruled out and the patient has a T-score that is less than or equal to -2.5 (also signifying -2.5 standard deviations from the mean).
  • It must be remembered that the first consideration for treatment in patients with secondary osteoporosis (caused by hyperparathyroidism, for example) should be focused on approach to correct the secondary cause. However, it is yet reasonable to pharmacologically treat the patient if the clinical scenario indicates it. This can be approached on an individual, clinical basis.
  • It is also reasonable to initiate pharmacologic treatment if any of the above criteria are not completely satisfied, based upon additional risk factors that may or may have not been included in the WHO fracture study.

Interpreting FRAX calculation

• Using a DXA measurement of the femoral neck, FRAX is calculated with at least the following information:
  • Current Smoking
  • Consumption of >3 alcoholic beverages a day
  • Rheumatoid Arthritis
  • Glucocorticoid use such as Prednisone, at any time of life - 5mg/day for equal to or more than 3 months (not necessarily consecutive).
  • Personal history of fracture not caused by a minor incident such as a low-impact fall. For example, high impact fractures.
  • Family history of fracture not caused by a minor incident such as a low-impact fall.
  • Age
    • FRAX cannot be calculated for any patient less than 40 y/o or above 90 y/o.
  • Weight
    • If the patient's weight is greater than 125Kg the patient's FRAX can be calculated, but is assumed to be a maximum weight of 125Kg for calculation.
  • Race
    • This is key! For example, African-Americans have been found to have less risk of fracture at the same BMD.
  • FRAX can be calculated without the DXA scan BMD of the femoral neck; however, it may be more desirable to apply an objective measurement.
    • In order to calculate FRAX without the DXA, personal risk factors and any and all causes of secondary osteoporosis must be comprehensively inquired in order to correctly stratify the patient's fracture risk. This can be done in the primary care setting without the need for any equipment other than internet access. This particular information is important to the interpretation of the DXA scan because with the use of a femoral neck BMD, it is no longer necessary to consider causes of secondary osteoporosis other than those listed above.

Reporting Findings

A brief outline of the findings should include:

• A declaration of the body part(s) studied using a definable type of equipment and technique.
• Any visual deformities of the body parts of interest or issues precluding diagnosis.
• The densities of the areas of interest and associated T or Z scores.
• The change in bone densities since last study and/or since the highest/lowest density the patient has had in the past.
• FRAX calculation (if indicated)
• Recommendations

Follow-Up scanning

• According to the ISCD Follow-up is appropriate when the expected change in BMD is ≥ the LSC
• Using the LSC alone as an indication of when to call something "significantly changed" is erroneous information and does not account for the expected change in BMD for a certain ROI with a certain type of therapy.
• The Monitoring Time Interval (MTI) can be calculated using the LSC:

$MTI = \frac {LSC}{(expected\ %\bigtriangleup per year)}\$

• When the MTI is ≤ 1.0 the measured change has exceeded the expected change for a given institution, treatment, and patient. Therefore, a repeat BMD at or after this time will result in clinically relevant information.
• LSC is calculated per the standards laid out by the ISCD (see iscd.org).
• Expected change per year is dependent on therapy type and where you measure.
• A simple method is to scan one year after initiating or changing therapy, and then at less frequent intervals once a pattern is evident.

Acronyms used

• BMD - Bone Mineral Density
• DXA - also known as DEXA; bone density scan
• FRAX - Fracture Risk Assessment Tool
• ISCD - International Society for Clinical Densitometry
• LSC - Least Significant Change (Usually at the 95% confidence interval)
• ROI - Region of interest
• VFA - Visual Fracture Analysis

References

• ^ PMID 19426925 - "2008 Santa Fe Bone Symposium: update on osteoporosis." Lewiecki EM, Baim S, Bilezikian JP, Eastell R, LeBoff MS, Miller PD. (J Clin Densitom. 2009 Apr-Jun;12(2):135-57.)
• WHO publication - Kanis JA, on behalf of the World Health Organisation Scientific Group. Assessment of osteoporosis at the primary health care level. WHO Collaborating Centre for Metabolic Bone Diseases, University of Sheffield 2007 (available on request from the WHO Collaborating Centre or the IOF).
• ^ Online FRAX calculation tool
• ^ iscd.org - International Society of Clinical Densitometry

Diagnosis	T-score
Normal	≥ -1.0
Low Bone Mass ("Osteopenia," "Low Bone Density")	> -2.5 and < -1.0
Osteoporosis	≤ -2.5
Severe ("Established") Osteoporosis	≤ -2.5 for young-adult women, with a history of fragility fracture