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.