How to interpret T score for patients with Down syndrome?

Interpreting T-scores in Patients with Down Syndrome

T-scores in patients with Down syndrome should not be interpreted using standard reference populations, as these patients have inherently different bone characteristics requiring specialized assessment and interpretation.

Understanding Bone Health in Down Syndrome

Patients with Down syndrome (DS) have unique skeletal characteristics that affect bone mineral density (BMD) measurements:

• Lower bone mass compared to the general population, particularly in males 1
• Smaller bone size that can affect standard DXA measurements 2
• Lower bone turnover with significantly decreased bone formation markers 1
• More rapid decline in volumetric BMD with age compared to the general population 2

Key Considerations for T-score Interpretation

Anatomical and Physiological Differences

• DS patients have smaller cortical thickness (1.84 mm vs 2.02 mm in controls) 2
• Lower cortical volumetric BMD (777 mg/cm³ vs 809 mg/cm³ in controls) 2
• Sexual dimorphism exists, with males showing more pronounced bone deficits than females 3, 2

Age-Related Considerations

• Bone mass deficits progress with age in both sexes but appear earlier in males 1, 3
• The decline in BMD is steeper in DS patients compared to the general population 2

Recommended Approach to T-score Interpretation

1. Use Z-scores instead of T-scores when possible

   • Z-scores compare to age-matched controls rather than young adult peak bone mass
   • More appropriate for populations with inherently different bone characteristics

2. Consider volumetric BMD assessment

   • 3D-SHAPER or similar software can derive volumetric measurements from DXA scans 2
   • Provides more accurate assessment by accounting for bone size differences

3. Evaluate for clinical risk factors specific to DS

   • Assess thyroid function (thyroid dysfunction is common in DS) 4
   • Evaluate for subtle signs of hypothyroidism, which can be difficult to detect in DS 4

4. Interpret fracture risk differently

   • DS patients have impaired fracture healing demonstrated in research models 3
   • Lower threshold for intervention may be warranted given healing challenges

Clinical Implications

• Standard WHO definitions (T-score > -1.0 as normal, -1.0 to -2.4 as osteopenia, ≤ -2.5 as osteoporosis) 4 may not apply appropriately to DS patients
• Antiresorptive therapy may not be optimal given that bone formation (not resorption) appears to be the primary deficit 1
• Exercise interventions have shown promise in improving bone mass in young people with DS 5

Pitfalls to Avoid

• Do not rely solely on T-scores for treatment decisions in DS patients
• Avoid assuming that osteoporosis in DS has the same pathophysiology as in the general population
• Do not automatically prescribe antiresorptive medications without considering the unique bone turnover profile in DS 1
• Be cautious about using FRAX or similar tools that have not been validated in the DS population