How likely are migraine patients to display dissemination in space?

Dissemination in Space in Migraine Patients

Migraine patients rarely display true dissemination in space (DIS) that would meet diagnostic criteria for multiple sclerosis, though up to 30% may have incidental white matter hyperintensities that could be misinterpreted as MS lesions. 1

Understanding Dissemination in Space

Dissemination in space refers to the presence of multiple demyelinating lesions in distinct anatomical locations within the central nervous system, which is a key diagnostic criterion for multiple sclerosis (MS). According to the McDonald criteria, DIS is demonstrated by:

• At least one T2 lesion in at least 2 of 5 locations characteristic for MS:
  • Periventricular
  • Cortical/juxtacortical
  • Infratentorial
  • Spinal cord
  • Optic nerve 1

Migraine and White Matter Lesions

While migraine patients can have white matter hyperintensities on MRI, these differ from true MS lesions in several important ways:

• Prevalence: Up to 30% of migraine patients may have incidental periventricular lesions 1
• Distribution: Migraine-related lesions typically do not display the characteristic MS pattern of dissemination
• Morphology: Migraine-related lesions are usually small, rounded, and deep white matter lesions that spare the periventricular zone and U-fibers 2

Distinguishing MS Lesions from Migraine-Related Lesions

To avoid misdiagnosis, the following characteristics suggest MS rather than migraine-related lesions:

• Periventricular lesions that are ovoid and perpendicular to the ventricles (Dawson's fingers)
• Presence of juxtacortical lesions
• Infratentorial lesions, especially in the pons
• Spinal cord lesions
• Gadolinium-enhancing lesions 1

Diagnostic Implications

The MAGNIMS consensus guidelines recommend requiring ≥3 periventricular lesions (rather than just 1) to improve specificity for MS when evaluating patients with migraine 1. This is crucial because:

1. Dissemination in space alone is insufficient for MS diagnosis
2. MS diagnosis requires both dissemination in space AND dissemination in time
3. There must be no better explanation for the clinical and paraclinical abnormalities 2, 1

Clinical Correlation

MRI findings must always be interpreted in the appropriate clinical context. Migraine patients with aura may present with symptoms that could be confused with MS, but these have distinct characteristics:

• Migraine aura symptoms typically:
  • Spread gradually over ≥5 minutes
  • Last 5-60 minutes per symptom
  • May include visual, sensory, speech/language symptoms
  • Are often followed by headache within 60 minutes 2

Avoiding Misdiagnosis

To avoid misdiagnosis of MS in migraine patients:

1. Apply more stringent criteria for periventricular lesions (≥3 rather than just 1)
2. Look for characteristic MS lesion morphology (ovoid, perpendicular to ventricles)
3. Remember that DIS alone is insufficient for MS diagnosis
4. Consider the entire clinical picture
5. Monitor for development of new lesions over time in cases of incidental findings 1

Pitfalls to Avoid

• Misclassifying white matter lesions that are close to but separated from the ventricular surface as periventricular 2
• Counting lesions touching the third and fourth ventricles as periventricular 2
• Diagnosing MS based solely on non-specific white matter lesions without appropriate clinical correlation
• Failing to recognize that both migraine and MS can coexist in the same patient 2

When evaluating migraine patients with white matter lesions, always remember that "there must be no better explanation for the clinical and paraclinical abnormalities than MS for a secure diagnosis to be made" 1.