What percentage of migraine patients fulfill the McDonald criteria for dissemination in space?

Percentage of Migraine Patients Fulfilling McDonald Criteria for Dissemination in Space

Approximately 24.4-34.5% of migraine patients may fulfill the McDonald criteria for dissemination in space (DIS), though these are incidental findings and do not indicate multiple sclerosis. 1

Understanding Dissemination in Space (DIS) Criteria

The McDonald criteria for DIS in multiple sclerosis (MS) diagnosis require evidence of lesions in specific locations of the central nervous system:

• According to the 2017 MAGNIMS consensus guidelines, DIS is demonstrated by at least one T2 lesion in at least 2 of 5 locations characteristic for MS 2:
  • Periventricular (≥3 lesions required)
  • Cortical/juxtacortical
  • Infratentorial
  • Spinal cord
  • Optic nerve (added in 2016 guidelines)

Migraine and MS-like MRI Findings

Migraine patients frequently show white matter hyperintensities (WMHs) on MRI that can mimic MS lesions:

• A study of 326 headache patients found that 51.5% had white matter hyperintensities 1
• Among patients with WMHs 1:
  • 24.4% met McDonald criteria when "touching" definition was used (lesions directly contacting ventricles/cortex)
  • 34.5% met McDonald criteria when a more liberal "within 3mm" definition was used

Distinguishing Migraine from MS

Several key factors help differentiate incidental WMHs in migraine from true MS lesions:

• Periventricular lesions are particularly important in differential diagnosis:

  • Up to 30% of migraine patients may have incidental periventricular lesions 2
  • The MAGNIMS consensus recommends requiring ≥3 periventricular lesions (rather than just 1) to improve specificity for MS 2

• Lesion characteristics that suggest MS rather than migraine include:

  • Periventricular lesions that are ovoid and perpendicular to the ventricles
  • Presence of juxtacortical lesions
  • Infratentorial lesions, especially in the pons
  • Spinal cord lesions
  • Gadolinium-enhancing lesions

Clinical Implications

The high prevalence of MS-like MRI findings in migraine patients has important implications:

• Risk of misdiagnosis: The overlap between migraine and MS imaging findings can lead to unnecessary concern and potential misdiagnosis
• Need for clinical correlation: MRI findings must always be interpreted in the appropriate clinical context 2
• Importance of follow-up: In cases of incidental findings, monitoring for development of new lesions over time may be necessary

Avoiding Diagnostic Pitfalls

To avoid misdiagnosis of MS in migraine patients with incidental MRI findings:

1. Remember that DIS alone is insufficient for MS diagnosis - dissemination in time (DIT) is also required 2
2. Consider that up to 34.5% of migraine patients may have incidental findings meeting DIS criteria 1
3. Apply more stringent criteria for periventricular lesions (≥3 rather than just 1) 2
4. Look for specific MS-like lesion characteristics (periventricular ovoid lesions, juxtacortical lesions)
5. Consider the entire clinical picture - MS diagnosis requires appropriate clinical presentation

Conclusion

While a substantial percentage (24.4-34.5%) of migraine patients may show MRI findings that fulfill McDonald criteria for dissemination in space, these findings alone do not indicate MS. The 2010 McDonald criteria emphasize that "there must be no better explanation for the clinical and paraclinical abnormalities than MS for a secure diagnosis to be made" 2, highlighting the importance of clinical correlation in the diagnostic process.