What is the role of a DEXA (Dual-Energy X-ray Absorptiometry) scan in screening for osteoporosis in patients with rheumatoid arthritis, particularly those with a history of prolonged corticosteroid use?

DEXA Scan Screening for Rheumatoid Arthritis Patients

All patients with rheumatoid arthritis should undergo baseline DEXA scanning of the lumbar spine and bilateral hips, particularly those with prolonged corticosteroid use (≥5 mg prednisone daily for ≥3 months), as RA itself doubles fracture risk independent of bone density, and glucocorticoid therapy further accelerates bone loss. 1

Primary Screening Recommendation

• DEXA of the lumbar spine (L1-L4) and bilateral hips (total hip and femoral neck) is the gold standard for osteoporosis screening in RA patients, providing accurate fracture risk prediction with established WHO diagnostic standards 1, 2
• The diagnosis is based on T-scores: normal (≥ -1.0), osteopenia (-1.0 to -2.5), and osteoporosis (≤ -2.5) 1
• RA patients have approximately double the risk of both vertebral and non-vertebral fractures compared to the general population, making screening particularly critical 3, 4

Specific Indications for RA Patients

Glucocorticoid Users

• Patients receiving or expected to receive glucocorticoid therapy for >3 months require baseline DEXA scanning 1, 5
• Research demonstrates that 70.4% of long-term corticosteroid users with RA have documented bone loss on DEXA, yet only 37% receive recommended baseline screening 6
• Glucocorticoid-induced osteoporosis represents a major but underrecognized complication in RA management 6

Additional High-Risk Features

• RA disease activity itself amplifies bone loss through inflammatory cytokines, independent of medication effects 3, 4
• Patients with RA autoantibodies show increased association with osteoporosis development 4
• Immobilization from active disease contributes to accelerated bone loss 3

Vertebral Fracture Assessment (VFA)

• VFA should be performed during the same DEXA session for RA patients with T-score < -1.0 and any of the following: 1, 2
  • Women aged ≥70 years or men aged ≥80 years
  • Historical height loss >4 cm
  • Self-reported but undocumented prior vertebral fracture
  • Glucocorticoid therapy equivalent to ≥5 mg prednisone daily for ≥3 months
• VFA is particularly valuable in RA because 30% of patients may have osteoporotic fractures (vertebral and/or non-vertebral) that influence management 7

Follow-Up Scanning Intervals

For Glucocorticoid Users

• 1-year intervals after initiation or change of therapy, with progressively longer intervals once therapeutic effect is established 1, 5, 8
• Patients at high risk for rapid bone mass decline require shorter monitoring intervals than standard recommendations 5, 8

For Other RA Patients

• Patients with baseline T-score < -2.0 or those with developing risk factors: every 2 years 1, 8
• Patients with T-score > -2.0 without additional risk factors: no routine follow-up unless new risk factors develop 8
• Scan intervals <1 year are discouraged as bone density changes occur slowly 1, 5

FRAX Risk Assessment Integration

• FRAX should be used in RA patients with osteopenia (T-score -1.0 to -2.5) to calculate 10-year fracture probability 1, 2
• FRAX factors include RA as a specific risk factor, along with glucocorticoid use >3 months 1
• Treatment is recommended when FRAX shows 10-year hip fracture risk ≥3% or major osteoporotic fracture risk ≥20% 1, 2

Alternative Imaging Modalities

Quantitative CT (QCT)

• QCT may be considered when DXA is limited by severe degenerative spine disease (common in RA) or obesity (BMI >35 kg/m²) 1
• Opportunistic CT screening can assess both vertebral fractures and bone density, identifying 74% of patients with osteoporotic fractures versus only 42% by DXA in one RA cohort 7
• QCT uses different diagnostic thresholds: osteopenia 80-120 mg/mL, osteoporosis <80 mg/mL 1, 2

Quantitative Ultrasound (QUS)

• QUS is NOT recommended for diagnosis or monitoring of osteoporosis in RA patients 1
• While QUS of the calcaneus shows 90% sensitivity for osteoporosis detection, specificity is only 44% with positive predictive value of 31% 9
• Meta-analysis confirms current literature does not support substituting QUS for DEXA in rheumatic diseases 1

Critical Technical Considerations

• Follow-up scans must be performed on the same DXA machine to ensure accurate comparison 1, 5, 8
• Compare BMD values, not T-scores, between serial scans 1, 5, 8
• Exclude vertebrae with artifacts (osteoarthritis, fractures, hardware) that spuriously increase BMD values 1
• Vertebrae differing by T-score ≥1.0 from adjacent vertebrae should be excluded from analysis 1

Common Clinical Pitfalls

• Underutilization is rampant: only 37% of long-term glucocorticoid users with RA receive recommended baseline DEXA scanning, and only 38.9% receive appropriate treatment 6
• Lumbar spine osteoarthritis (present in 40% of women aged 55 and 85% aged >75) can mask true bone loss by artificially elevating BMD 1
• Vertebral fractures increase BMD values by mean 0.070 g/cm² due to trabecular impaction, potentially masking osteoporosis 1
• Failing to account for RA disease activity when interpreting results—active inflammation accelerates bone loss beyond medication effects 3, 4

Treatment Implications

• When non-treated RA patients show statistically significant BMD decrease on follow-up, therapy initiation should be considered 1, 8
• Serial BMD testing combined with clinical risk factors, bone turnover markers, height loss, and trabecular bone score (TBS) guide treatment decisions 1, 8
• TBS is particularly useful in RA patients, as it shows increased fracture risk even with normal BMD in those on glucocorticoid therapy 1
• Anti-TNF-α therapy that controls RA disease activity helps prevent generalized bone loss, though fracture outcome data remain limited 3