What are the criteria for a DEXA (Dual-Energy X-ray Absorptiometry) scan in a patient on Depo-Provera (medroxyprogesterone acetate) for more than five years, according to New Zealand guidelines?

DEXA Scan Criteria for Patients on Depo-Provera for More Than Five Years in New Zealand

Patients who have been on Depo-Provera (medroxyprogesterone acetate) for more than five years should undergo DEXA scanning due to the significant bone mineral density loss associated with long-term use.

Evidence-Based Rationale

The FDA drug label for medroxyprogesterone acetate clearly states that long-term use (>5 years) is associated with significant bone mineral density (BMD) loss 1:

• Adult women using Depo-Provera for up to 5 years show spine and hip BMD mean decreases of 5-6%
• The decline is more pronounced during the first two years of use, with smaller declines in subsequent years
• Mean changes in lumbar spine BMD of -2.86%, -4.11%, -4.89%, -4.93%, and -5.38% after 1,2,3,4, and 5 years, respectively

Specific Criteria for DEXA Scanning in Depo-Provera Users

Based on the available guidelines, DEXA scanning is indicated for:

1. Duration of Use:

   • Any patient who has used Depo-Provera for more than 5 years 2
   • This is considered a high-risk factor for bone loss

2. Additional Risk Factors (increasing urgency for DEXA):

   • Low body weight (BMI <18.5) 2
   • Family history of osteoporosis 3
   • Current or past smoking 3
   • Concurrent medications that affect bone (such as glucocorticoids) 2
   • Other medical conditions associated with bone loss 2

3. Previous Fracture History:

   • Any prior fragility fracture 2
   • One or more non-peripheral fractures or two or more peripheral long bone fractures 2

Recommended DEXA Scan Sites

For adult women ≥20 years on Depo-Provera:

• Weight-bearing sites: posteroanterior spine, total hip, femoral neck 2
• Non-weight-bearing sites (radius 33%) only if weight-bearing sites cannot be assessed 2

For women <20 years on Depo-Provera:

• Posteroanterior lumbar spine BMC and areal BMD
• Whole body less head (if possible) BMC and areal BMD 2

Follow-up DEXA Scanning

• Repeat DEXA scanning should be performed every 1-2 years to assess ongoing bone loss or recovery 2, 4
• More frequent monitoring (annually) may be appropriate for those with significant risk factors 2

Important Clinical Considerations

1. Partial Recovery After Discontinuation:

   • After stopping Depo-Provera, there is only partial recovery of BMD toward baseline values during the 2-year post-therapy period 1
   • Longer duration of treatment is associated with less complete recovery 1

2. Adolescent Concerns:

   • Adolescents treated with Depo-Provera for more than 2 years may not recover to baseline BMD levels at femoral neck and total hip even up to 60 months post-treatment 1

3. Interpretation of Results:

   • For adults: T-scores should be used for diagnosis
   • For adolescents and young women <20 years: Z-scores should be used, adjusted for height or height age 2

Clinical Pitfalls to Avoid

1. Underestimating Risk: Do not dismiss the need for DEXA scanning in women with >5 years of Depo-Provera use, even if they are asymptomatic or have no other risk factors.

2. Inappropriate Timing: Ensure DEXA scans are performed on the same machine when possible for accurate comparison of sequential results.

3. Misinterpretation: For young women, ensure Z-scores (not T-scores) are used for assessment and interpretation.

4. Inadequate Follow-up: After discontinuation of Depo-Provera, continue monitoring BMD as recovery may be incomplete, especially with longer duration of use.