Why Has My Bone Density Increased?: Understanding Unexpected Test Results

Typically, bone mass naturally declines with age, especially after peak bone mass is reached around age 30. However, receiving a bone density scan result that shows an increase can be confusing and lead to the question, "why has my bone density increased?" This unexpected finding can be the result of a number of factors, including treatment effects, lifestyle changes, or underlying medical conditions.

Quick Summary

An increase in bone density can result from successful osteoporosis treatment, significant weight-bearing exercise, or artifacts caused by conditions like osteoarthritis. It can also point to rare genetic disorders, such as osteopetrosis, or other acquired medical issues. A specialist's assessment is crucial to properly interpret this surprising result.

Key Points

• Positive Response to Treatment: Certain medications for osteoporosis, such as bisphosphonates or anabolic agents, are designed to increase bone density.

• Artifacts on the Scan: Degenerative conditions like osteoarthritis, particularly in the spine, can artificially inflate DXA scan results by increasing mineral density in localized areas.

• Genetic Conditions: High bone mass can be caused by rare genetic disorders like osteopetrosis or LRP5 High Bone Mass syndrome.

• Lifestyle Factors: Significant weight gain or consistent weight-bearing exercise can put more mechanical stress on bones, leading to a natural increase in density.

• Further Medical Evaluation: An unexpectedly high bone density reading, especially if unexplained, warrants a detailed medical evaluation to rule out underlying systemic or rare disorders.

• Fracture Healing: Localized increased density or callus formation can occur at the site of a healing fracture.

Interpreting Surprising Scan Results

An unexpected increase in bone mineral density (BMD), as measured by a Dual-energy X-ray Absorptiometry (DXA) scan, warrants careful review. While bone loss is the more common concern, particularly in older adults, a higher-than-expected reading requires a nuanced interpretation. The cause could range from a successful treatment to the presence of an artifact that affects the reading, or in rare cases, a more serious underlying condition.

Potential Causes for Increased Bone Density

Several factors can contribute to an elevated bone mineral density reading. These can be broadly categorized into treatment-related causes, medical conditions, and external or lifestyle influences.

Medications for Osteoporosis

One of the most common reasons for an increased BMD is the successful treatment of osteoporosis. Medications designed to halt bone loss or actively build new bone tissue will lead to higher density readings over time.

• Bisphosphonates: Drugs like alendronate (Fosamax) and risedronate (Actonel) work by slowing down the bone breakdown process, allowing bone formation to catch up. Consistent use of these medications often results in a measurable increase in BMD.
• Anabolic Agents: These medications, such as teriparatide (Forteo), stimulate new bone formation by mimicking a natural parathyroid hormone. They can lead to significant increases in BMD over a relatively short period.
• Denosumab: This medication works by blocking a key protein needed for osteoclast formation and function, thereby inhibiting bone resorption.

Lifestyle and Biomechanical Factors

Certain lifestyle changes and physical attributes can influence bone density readings.

• Weight-Bearing Exercise: Regular engagement in activities that put stress on the bones, such as weightlifting, running, or even brisk walking, can stimulate bone growth and increase density.
• Increased Body Mass Index (BMI): A higher body weight places more mechanical stress on the skeleton, which can lead to higher BMD readings.

Medical Conditions

In some instances, increased bone density is a sign of an underlying medical condition, which may be genetic or acquired.

Genetic Conditions

Rare genetic disorders can cause high bone mass, sometimes resulting in bones that are abnormally dense but paradoxically brittle.

• Osteopetrosis: A group of rare disorders where bones become abnormally dense and brittle due to a defect in the cells that break down old bone. Diagnosis can be made through radiography, genetic testing, and other lab studies.
• LRP5 High Bone Mass Syndrome: A rare genetic condition where mutations in the LRP5 gene lead to an overactivation of bone formation pathways, resulting in exceptionally high bone density.

Acquired Conditions

These conditions are not inherited but develop over time.

• Degenerative Disc Disease and Osteoarthritis: A very common cause of high BMD, particularly in the spine. Arthritic changes, bony growths (osteophytes), and scoliosis can artificially elevate DXA readings in the lumbar spine. This is a crucial distinction to make, as it doesn't represent a true increase in overall bone health.
• Renal Osteodystrophy: In patients with advanced kidney disease, this metabolic bone disorder can sometimes present as increased bone density, particularly affecting the axial skeleton.
• Healing Fractures: An earlier fracture, now in the process of healing, can create a localized area of increased mineral content or callus formation, which can be reflected in a DXA scan of that region.
• Other Causes: Other, though less common, acquired causes include certain cancers (osteoblastic metastases), fluorosis, and hormonal imbalances like acromegaly.

Differentiating True Increase from Artifacts

Properly interpreting DXA results requires distinguishing between a true, systemic increase in bone density and a localized artifact. A radiologist or endocrinologist can help identify these nuances.

T-Scores vs. Z-Scores

• T-Score: Compares your bone density to a healthy 30-year-old adult of the same sex. A positive T-score indicates bone density is higher than the young adult mean.
• Z-Score: Compares your bone density to the average of someone of the same age, sex, and ethnicity. A Z-score greater than +2.0 is often defined as an unusually high BMD and may prompt further investigation.

DXA Scan Artifact Comparison

Feature	True BMD Increase (Systemic)	Artifact (Localized)
Cause	Medications, genetics, systemic disease.	Degenerative changes (arthritis), scoliosis, aortic calcification.
Location	Affects multiple sites (spine, hip, wrist).	Often localized to a single area, most commonly the lumbar spine.
Symmetry	Tends to be symmetrical across the skeleton.	Can be asymmetrical, depending on the artifact's location.
Z-Score	May be significantly positive (e.g., > +2.0).	Could be misleadingly high at a single site due to local factor.

What to Do After an Increased BMD Reading

If you receive a DXA result showing increased bone density, the next step is not to celebrate but to investigate. A specialist can help pinpoint the cause and determine if any action is needed.

1. Review your medical history: Discuss recent medications, particularly osteoporosis treatments, with your doctor.
2. Examine previous scans: Comparing the new DXA scan to previous ones can help determine if the increase is new or part of a longer-term trend.
3. Consider further testing: Depending on the results, your doctor may recommend additional imaging (like x-rays) or laboratory tests to rule out other medical conditions.
4. Assess lifestyle factors: Evaluate if changes in exercise or weight could have influenced the reading.

Conclusion

An increase in bone density is an important finding that can have multiple explanations. While it may indicate a positive response to treatment, it can also point to artifactual issues or more complex underlying conditions. For a clear understanding of your specific situation, it is essential to consult with a healthcare professional who can properly interpret the results and guide you on the next steps.

To learn more about bone health and conditions, you can visit the National Institutes of Health website.

Frequently Asked Questions

Can I have increased bone density and still be at risk for fractures?

Yes. This is a critical distinction. In some rare genetic conditions like osteopetrosis, the bones are very dense but also abnormally brittle, making them more prone to fracture despite the high density reading.

How can I tell if my high bone density reading is just an artifact?

A doctor or radiologist can help interpret the DXA scan images. Artifacts, such as those from degenerative arthritis or vascular calcifications, often appear in specific areas like the lumbar spine and may be accompanied by other visible changes on the image.

Does taking calcium supplements cause increased bone density?

While adequate calcium is essential for bone health, simply taking supplements is unlikely to cause a significant, surprising increase in bone density on its own. It's one piece of the puzzle, alongside other factors like vitamin D and exercise.

Is high bone density always a good thing?

Not necessarily. While normal-to-high bone density is generally healthy, extremely high density caused by genetic disorders (like osteopetrosis) can weaken the bones or lead to other health issues, such as nerve compression.

Should I change my osteoporosis medication if my bone density increased?

Do not alter your medication regimen without consulting your doctor. An increase in BMD may indicate the medication is working effectively, but your physician will need to assess the overall treatment plan and your specific situation.

How does exercise increase my bone density?

Weight-bearing and resistance exercises stimulate bone-forming cells (osteoblasts) to produce more bone tissue. The mechanical stress placed on the skeleton during these activities strengthens and increases the density of the bones over time.

What is the difference between a T-score and a Z-score for bone density?

A T-score compares your bone density to that of a healthy young adult, while a Z-score compares it to people of your same age, sex, and ethnicity. For an unusually high reading, the Z-score is particularly relevant, and a Z-score above +2.0 often warrants further investigation.