What is the recommended frequency for performing the Symbol Digit Modalities Test (SDMT) in patients with Multiple Sclerosis (MS)?

Frequency of Symbol Digit Modalities Test (SDMT) in Multiple Sclerosis Patients

The recommended frequency for performing the Symbol Digit Modalities Test (SDMT) in patients with Multiple Sclerosis (MS) is every 6 months. 1

Rationale for SDMT Testing Frequency

• SDMT is one of the most reliable and sensitive measures of cognitive function in people with MS, making it valuable for monitoring cognitive changes over time 2, 3
• While no specific guidelines directly address SDMT testing frequency in MS, expert consensus supports a 6-month interval between cognitive assessments in patients with neurological conditions 1
• The 6-month interval allows for detection of significant changes in cognitive function while minimizing practice effects that can occur with more frequent testing 4
• This testing frequency aligns with other monitoring recommendations for MS patients, such as follow-up brain MRI scans which are recommended every 3-6 months depending on risk factors 1

Implementation Considerations

• When administering SDMT at 6-month intervals:

  • Use alternate forms when available to minimize practice effects, as repeated exposure to the same test can lead to improved scores (approximately 1.8 points per repetition) that don't reflect true cognitive improvement 4
  • Be aware that improvements in SDMT performance are greatest when repeating the same form over brief intervals, which could mask actual cognitive decline 4
  • Consider that testing intervals exceeding two years may show SDMT decline that doesn't accurately reflect the patient's cognitive trajectory 4

• The oral version of the SDMT is typically preferred for MS patients to avoid motor function confounds 5

  • Performance is influenced by age, gender, and education level, with scores generally declining with age (most notably after age 30), women performing better than men (average 5.1 points higher), and education effects most apparent in ages 25-54 5

Special Monitoring Considerations

• More frequent monitoring (every 3-4 months) may be warranted in:

  • Patients at high risk for progressive multifocal leukoencephalopathy (PML), such as those on natalizumab who are JCV seropositive with treatment duration ≥18 months 1, 6
  • Patients who have switched from natalizumab to other therapeutics, requiring enhanced pharmacovigilance for up to 12 months 6
  • Patients with highly active disease or severe, life-threatening presentations 7

• Less frequent monitoring (annually) may be appropriate for:

  • Patients with stable disease and low risk of complications 1, 6
  • Patients with slowly progressing forms of MS 1

Clinical Utility of SDMT

• A score of 55 or lower on the SDMT accurately identifies cognitive impairment in 72% of MS patients (sensitivity 0.82, specificity 0.60) 3
• The test can be administered and scored in approximately 5 minutes, making it practical for routine clinical use 3
• Both paper and computerized versions of SDMT show good validity in detecting cognitive dysfunction in MS patients 8
• Test-retest correlations are high (ranging from 0.89 to 0.96), supporting its reliability for monitoring over time 2

Integrating SDMT with Other Monitoring

• SDMT should be part of a comprehensive monitoring approach that includes:
  • Regular brain MRI scans with T2-weighted, FLAIR, and contrast-enhanced T1-weighted sequences to detect new or enlarging lesions 1, 7
  • Assessment of disease-modifying therapy effectiveness 7
  • Evaluation for potential treatment adjustments in patients with evidence of disease progression 7