Bone Mineral Density: Back to the Basics Beth Chasen,, MD Assistant Professor MD Anderson Cancer Center
Bone Densitometry (DXA)- who needs an evaluation? Women aged 65 and older. Postmenopausal women under age 65 with risk factors. Men aged 70 and older. Adults with a fragility fracture. Adults with a disease or condition associated with low bone mass or bone loss. Adults taking medications associated with low bone mass or bone loss. Anyone being considered for pharmacologic therapy. Anyone being treated, to monitor treatment effect. Anyone not receiving therapy in whom evidence of bone loss would lead to treatment. Slides are not to be reproduced
DXA- who needs an evaluation? Every MDACC patient fits on this list! Aging population Receiving chemotherapy, XRT, bone marrow transplants Slides are not to be reproduced
DXA- how does it work? Xrays of two different energy peaks are generated Different attenuation for both soft tissue and bone Use equation within software to compare Slides are not to be reproduced
DXA- what about the numbers? Bone Mineral Content (BMC) Measured in grams Determined by differing attenuation based on region selected as bone Will be affected by high or low density artifact Slides are not to be reproduced
DXA- what about the numbers? Bone Mineral Density (BMD) Bone Mineral Content (g) / area (cm2) Greatly affected by selected region of interest size Slides are not to be reproduced
T-score DXA- what about the numbers? Number of standard deviations a BMD measurement is above or below the mean peak bone mass of a young (20-35yrs) normal population Normal: T-score T -1.0 or greater Low bone mass/osteopenia: T-score T -1.1 to -2.4 Osteoporosis: T-score T -2.5 or less Slides are not to be reproduced
Z-score DXA- what about the numbers? Number of standard deviations above or below mean reference value for an age, sex, and race matched population Used in premenopausal women and men < 50 yrs Used in children -2.0 or lower is below the expected range for age Slides are not to be reproduced
WE CAN GENERATE NUMBERS HOW DO WE KNOW THE NUMBERS PROVIDE USEFUL DATA? Slides are not to be reproduced
Accuracy vs. Precision Accuracy How close to correct result? Precision How well do repeated attempts coincide? Slides are not to be reproduced
Accuracy and Precision BOTH ARE CRUCIAL Achieving accuracy Ideal initial positioning Proper region of interest selection Achieving precision Repetition of ideal initial positioning and ROI selection Slides are not to be reproduced
Precision error Least significant change in BMD with 95% confidence Describes/defines changes in BMD that are not statistically significant Slides are not to be reproduced
Precision error Minimum standards for technologist (BMD % change) Lumbar spine: 5.3% Total hip: 5.0% Femoral neck: 6.9% Slides are not to be reproduced
Precision error System likely assumes better precision than minimum Need to determine own precision error 30 patients evaluated twice Results from different technologists averaged Slides are not to be reproduced
Example Slides are not to be reproduced
5.1% femoral neck increase in 2 weeks Must be precision error! Which is accurate? Slides are not to be reproduced
Neither is actually accurate With minor modification, can improve Images are within minimum acceptable standard for precision Illustrates need for customized significant change standards Slides are not to be reproduced
Hip/Femoral Neck POSITIONING IS CRITICAL! Hip rotation is responsible for majority of precision errors Slides are not to be reproduced
Hip/Femoral Neck Cortical bone Outer portion More dense Trabecular bone Varying portion of bone middle Less dense Slides are not to be reproduced
Hip/Femoral neck Trochanteric region and femoral neck have large percentage of trabecular bone More likely to fracture Falsely elevate BMD by including femoral shaft Slides are not to be reproduced
EXAMPLE 1 Slides are not to be reproduced
EXAMPLE 1 14.6% femoral neck drop in <2 years Poor initial positioning Probable overestimation of initial neck BMD from excess cortical bone inclusion Forced to use new exam as new baseline Can hopefully use spine, opposite hip for determining trend Slides are not to be reproduced
EXAMPLE 2 Slides are not to be reproduced
EXAMPLE 2 14.9% femoral neck drop in one year Poor interval positioning 13.5% increase 2004 to 2005, no therapy Mistake perpetuated in 2006 Corrected positioning 2007 Confirmed at 6 month followup Slides are not to be reproduced
EXAMPLE 3 Slides are not to be reproduced
EXAMPLE 3 7% total hip decrease in 2 years Significant change but IS IT VALID? Problems Different total areas Can adjust retrospectively Suboptimal followup positioning Use first exam as accurate study Evaluate trend based on spine, opposite hip Slides are not to be reproduced
EXAMPLE 4 Slides are not to be reproduced
EXAMPLE 4 6% total hip drop in one month Statistically significant but not valid Problems Different total areas Improper initial inclusion of femoral shaft Can correct retrospectively Positioning difference Slides are not to be reproduced
EXAMPLE 5 Slides are not to be reproduced
EXAMPLE 5 Same day decline in T-score T from -2.2 to -2.5 Category moves from osteopenic to osteoporotic Slides are not to be reproduced
EXAMPLE 5 Importance of correct bone mapping Program may deselect osteoporotic bone Will cause incorrect elevation of T-scoreT Slides are not to be reproduced
Artifacts Elevate BMD Metallic/high density foreign bodies Oral/rectal contrast Compression fracture Calcium deposits In degenerative change In vascular structures Sclerotic lesions Slides are not to be reproduced
Artifacts Decrease BMD Lytic lesions Prior surgery Laminectomy Slides are not to be reproduced
Osteoporosis Definition: Disease characterized by low bone mass with structural deterioration of bone structure Causes bone fragility with susceptibility to fracture Osteopenia is a low bone mass state, less severe than osteoporosis Slides are not to be reproduced
Osteoporosis- A major health concern Affects 10 million in U.S. 8 million women, 2 million men Another 34 million at risk with osteopenia 55 percent of adults over 50 years Slides are not to be reproduced
Osteoporosis- A major health concern The price of fracture Responsible for 1.5 million fractures yearly One in two women and one in four men over 50 years will have osteoporosis related fracture in his/her lifetime 18 billion dollars in health care costs (2002) Slides are not to be reproduced
The human cost Osteoporosis- A major health concern 25 percent with hip fracture over 50 years die within one year 1 in 5 end up in nursing home At 6 months, only 15% can walk across a room unaided Slides are not to be reproduced
Osteoporosis- Risk factors Aging Female Thin/small frame Caucasian/Asian Family history Low estrogen/testosterone states Slides are not to be reproduced
Inactivity Low calcium intake Current smoking Excessive alcohol use Medications Steroids Anticonvulsants Chemotherapy Osteoporosis- Risk factors Slides are not to be reproduced
Osteoporosis- The silent disease NO SYMPTOMS UNTIL FRACTURE OCCURS! Bone mineral density tests can detect low bone mass before fracture Also follow rate of bone loss or response to therapy Slides are not to be reproduced
Treatment Options Calcium supplementation Vitamin D Estrogen therapy Parathyroid hormone (Forteo) Bisphosphonates Alendronate (Fosamax) Ibandronate (Boniva( Boniva) Risedronate (Actonel) Slides are not to be reproduced
Treatment Options Bisphosphonates Act as antiresorptive to slow turnover rate of bone Side effects Esophageal irritation Other GI symptoms Osteonecrosis Slides are not to be reproduced