🧠 McDonald Diagnostic Criteria Simulator

The Clinically Isolated Syndrome

A single demyelinating episode opens the diagnostic workup.

• 20–40: Typical age of onset (years, female-predominant)
• Optic neuritis: Common first symptom (or limb sensory loss)
• ~60–80%: CIS to MS conversion (over long-term follow-up)
• 2017: Criteria version used (McDonald revision)

What counts as a qualifying episode

Short placeholder: episode must reflect acute CNS demyelination, lasting >24 hours.

Why early diagnosis matters

Short placeholder: earlier treatment start correlates with better long-term outcomes.

Placeholder insight: the 2017 criteria let MS be diagnosed after just one attack.

Mapping Lesions Across Four CNS Regions

MRI screens four characteristic regions for demyelinating lesions.

• 4: Regions assessed (periventricular, cortical, infratentorial, cord)
• T2/FLAIR: Sequence used (plus gadolinium T1)
• ≥3 mm: Typical lesion size (ovoid, well-demarcated)
• 1.5–3T: Field strength (standard clinical MRI)

The four characteristic regions

Short placeholder: periventricular, cortical/juxtacortical, infratentorial, spinal cord.

Why region location matters

Short placeholder: distinct regions reflect disease spread through separate CNS pathways.

DIS — Lesions Across the CNS

DIS requires lesions in at least two of four regions.

• ≥2 / 4: DIS threshold (regions involved)
• Added 2017: Optic nerve status (as a fifth candidate region)
• Included: Symptomatic lesions (now count toward DIS)
• Improved: Sensitivity vs 2010 (earlier DIS detection)

Counting regions toward DIS

Short placeholder: one or more lesions per region qualifies that region.

Clinical significance of DIS

Short placeholder: DIS shows disease is spatially widespread in the CNS.

Placeholder insight: DIS alone is not sufficient — DIT is still required.

DIT — Evidence That Disease Evolves Over Time

DIT can be shown by new lesions, mixed enhancement, or CSF bands.

• New lesion: Path 1 (on follow-up MRI)
• Gd+/Gd−: Path 2 (simultaneous on one scan)
• CSF bands: Path 3 (oligoclonal bands substitute)
• Any time: Follow-up interval (no minimum interval required)

Three ways to satisfy DIT

Short placeholder: new T2 lesion, mixed enhancement, or CSF oligoclonal bands.

CSF oligoclonal bands as substitute

Short placeholder: bands allow earlier diagnosis without a second MRI.

Combining DIS and DIT Into a Diagnosis

Meeting both DIS and DIT confirms a diagnosis of MS.

• MS confirmed: DIS + DIT met (both criteria satisfied)
• CIS: One criterion met (clinically isolated syndrome)
• Insufficient: Neither met (continued monitoring advised)
• ~5–10%: Misdiagnosis rate (reported in MS clinics)

The final diagnostic decision rule

Short placeholder: DIS and DIT together, with no better explanation, confirm MS.

When criteria are not met

Short placeholder: patients are monitored clinically and with repeat imaging.

Placeholder insight: differential diagnoses must be excluded before confirming MS.