Multiple Sclerosis
What Do You Need to Know?
- McDonald 2017 criteria (RITE/board standard): diagnosis requires dissemination in space (DIS: ≥2 of 4 CNS regions — periventricular, cortical/juxtacortical, infratentorial, spinal cord) AND dissemination in time (DIT: simultaneous Gd+ and non-enhancing lesions, new lesions on follow-up, OR CSF-specific OCBs). McDonald 2024 revisions (supplementary): optic nerve added as a 5th DIS region (via MRI orbits, OCT, or VEP); supportive diagnostic biomarkers now include central vein sign, paramagnetic rim lesions, and CSF kappa free light chains; RIS may qualify as MS only when DIS is met with additional supportive evidence and no better alternative.
- Subtypes: CIS → RRMS (85%) → SPMS; PPMS (10–15%) is primary progressive from onset; Lublin 2014 adds active/inactive and progressing/not progressing modifiers
- Classic presentations: optic neuritis (painful vision loss, RAPD), INO (MLF lesion), partial transverse myelitis, Lhermitte sign, Uhthoff phenomenon
- MRI hallmarks: periventricular Dawson fingers, ovoid lesions perpendicular to ventricles, open ring enhancement, central vein sign, short spinal cord lesions (<2 vertebral segments)
- CSF: ≥2 oligoclonal bands unique to CSF (85–95%); elevated IgG index; CSF-specific OCBs can substitute for DIT in McDonald 2017
- Acute relapses: IV methylprednisolone 1 g/day × 3–5 days; PLEX for steroid-refractory relapses; oral prednisone alone is NOT recommended for optic neuritis
- Prognosis: favorable — young onset, female, sensory/ON presentation, RRMS; poor — male, older onset, motor/cerebellar symptoms, PPMS, high lesion burden
- McDonald 2017 criteria: diagnosis requires DIS (≥2 of 4 CNS regions: periventricular, cortical/juxtacortical, infratentorial, spinal cord) AND DIT (simultaneous Gd+ and non-enhancing lesions, OR new lesion on follow-up MRI). CSF-specific OCBs can substitute for DIT when DIS is met but DIT is not yet demonstrated.
- Lhermitte sign (electric shock down spine with neck flexion → cervical dorsal column plaque) and Uhthoff phenomenon (transient worsening with heat/exercise/fever — 0.5°C drop in conduction) are classic MS pearls; both are demyelination phenomena, not relapses, and do NOT require treatment escalation.
- Internuclear ophthalmoplegia (INO): impaired adduction of ipsilateral eye with nystagmus of contralateral abducting eye on lateral gaze — bilateral INO in a young woman is MS until proven otherwise; lesion in MLF between CN III and CN VI nuclei.
- Optic neuritis: painful monocular vision loss with RAPD, dyschromatopsia, central scotoma. If pain is absent (“atypical optic neuritis,” AON), suspect NMOSD (AQP4) or MOGAD — check serum AQP4-IgG and MOG-IgG before calling it MS. Bilateral simultaneous ON, severe vision loss (<20/200), longitudinally extensive optic nerve enhancement, or chiasmal involvement also favor NMO/MOG.
- 6 MRI lesion features to memorize: (1) periventricular ovoid Dawson fingers perpendicular to ventricles, (2) juxtacortical/cortical lesions (highly MS-specific), (3) infratentorial (pons/cerebellar peduncles), (4) short spinal cord lesions <2 vertebral segments, (5) T1 black holes (chronic axonal loss), (6) Gd-enhancing lesions = active inflammation. Contrast with NMO/MOG: LETM ≥3 vertebral segments, area postrema lesions, large fluffy MOG brainstem/ADEM-like lesions.
- Highly active MS → high-efficacy DMT early: B-cell depletion (ocrelizumab, ofatumumab, rituximab) or natalizumab (anti-VLA-4). Natalizumab + JCV seropositivity → PML risk rises sharply after 2 years and with prior immunosuppression; monitor JCV antibody index every 6 months and surveillance MRI. Ocrelizumab is the only DMT approved for PPMS.
- Pregnancy and MS: relapse rate decreases ~70% in third trimester (Th2 shift) and rebounds in the first 3 months postpartum. Safer options peri-conception: glatiramer acetate and interferon-β (compatible with pregnancy and breastfeeding); natalizumab can be continued in selected high-activity patients through early pregnancy; avoid teriflunomide (teratogenic — cholestyramine washout required), fingolimod, and cladribine.
- PML vs PPMS — do NOT confuse: PML = progressive multifocal leukoencephalopathy (JC virus reactivation, subcortical confluent non-enhancing T2 lesions crossing U-fibers, seen with natalizumab/fingolimod/rituximab); PPMS = primary progressive MS (steady neurologic decline from onset, no relapses, often myelopathy in older male). New non-enhancing subcortical T2 lesion in a natalizumab patient → stop drug, do CSF JCV PCR.
- Tumefactive MS and Marburg variant: tumefactive = single large (>2 cm) ring-enhancing lesion with open (incomplete) ring enhancement open toward cortex, vasogenic edema, mass effect — mimics tumor/abscess; biopsy shows demyelination with macrophages. Marburg variant = fulminant monophasic MS, rapid progression to death within weeks/months; treat aggressively with IV steroids, PLEX, and induction immunotherapy.
- Pediatric MS: <18 years, ~3–5% of MS; higher relapse rate but slower disability accrual; large T2 lesions and posterior fossa involvement are common; must exclude ADEM (monophasic, encephalopathy, polyfocal) and MOGAD. For US boards: fingolimod is the only FDA-labeled DMT for relapsing MS in patients age 10 years and older. Teriflunomide and dimethyl fumarate are labeled for adults in the US (pediatric efficacy was not established for teriflunomide; DMF's US label is adult-only); non-US pediatric labeling and off-label use should be considered separately. Early high-efficacy therapy increasingly favored.
Clinical phenotype
- Electric shock down spine with neck flexion → Lhermitte sign (cervical dorsal column MS plaque)
- Transient blurred vision after hot shower or exercise → Uhthoff phenomenon
- Bilateral impaired adduction with abducting eye nystagmus in young woman → Bilateral INO → MS (MLF lesion)
- Painful monocular vision loss with RAPD (Marcus Gunn pupil) and dyschromatopsia → Optic neuritis (MS)
- Painless severe bilateral simultaneous optic neuritis with chiasmal enhancement → NMOSD / MOGAD (NOT MS)
- Brief recurrent painful tonic posturing of limb triggered by movement → Paroxysmal tonic spasms of MS
- Loss of fine finger control / proprioception with preserved strength → Useless hand of Oppenheim (cervical dorsal column plaque)
- Disabling fatigue out of proportion to exam, worse with heat → MS-related fatigue
MRI / OCT signs
- Ovoid periventricular lesions perpendicular to corpus callosum on sagittal FLAIR → Dawson fingers (MS)
- Hypointense T1 lesions in chronic plaques → T1 black holes (axonal loss / chronic MS)
- Open (incomplete) ring enhancement on post-contrast T1 → Tumefactive MS / acute demyelinating lesion
- Small central venule running through an ovoid T2 lesion on SWI/FLAIR* → Central vein sign (MS-specific, McDonald 2024 biomarker)
- Paramagnetic iron rim around chronic lesion on SWI → Paramagnetic rim lesion (chronic active / smoldering MS)
- Juxtacortical and leukocortical lesions on 7T MRI / DIR → Highly MS-specific cortical demyelination
- Short spinal cord lesion <2 vertebral segments, dorsolateral, partial cross-section → MS myelitis
- Longitudinally extensive transverse myelitis (LETM) ≥3 vertebral segments, central cord → NMOSD / MOGAD (NOT MS)
- Thinning of retinal nerve fiber layer (RNFL) on OCT after optic neuritis → Post-ON axonal loss (MS biomarker)
CSF / pathology
- ≥2 oligoclonal bands unique to CSF (not in serum) on isoelectric focusing → CSF-specific OCBs (satisfy DIT in McDonald 2017)
- Elevated CSF kappa free light chains → Intrathecal B-cell activity (McDonald 2024 supportive biomarker)
- Mildly elevated IgG index (>0.7) with normal cell count and protein → MS CSF profile
- Perivenular demyelination with relative axonal sparing and reactive astrogliosis → MS demyelinating plaque
- Subpial and pan-cortical (leukocortical) demyelinated lesions → Highly MS-specific gray matter pathology (not seen in NMO/MOG/ADEM)
- Leptomeningeal contrast enhancement on post-contrast FLAIR with cortical lesions → Aggressive cortical / meningeal MS
- Aquaporin-4 IgG positive serum, LETM, area postrema syndrome → NMOSD (NOT MS)
- MOG-IgG positive serum with fluffy brainstem / ADEM-like lesions, often pediatric → MOGAD (NOT MS)
Epidemiology
Key Epidemiological Data
| Feature | Details |
|---|
| Prevalence | ~1 million in the US; ~2.8 million worldwide |
| Female:Male ratio | 3:1 (increasing over time, especially in RRMS); PPMS is ~1:1 |
| Age of onset | 20–40 years (peak ~30); PPMS peaks later (~40–50 years) |
| Geographic gradient | Prevalence increases with distance from equator; highest in Northern Europe, Canada, northern US |
| Migration effect | Migrating before age 15 adopts risk of destination country; after age 15, retains risk of origin |
| Vitamin D | Low serum 25(OH)D associated with ↑ MS risk and ↑ relapse rate; partially explains latitude gradient |
| EBV association | Strongest environmental risk factor; OR >30 for MS after EBV seroconversion; virtually all MS patients are EBV seropositive |
| Smoking | 1.5× increased risk; dose-dependent; accelerates conversion to SPMS |
| Genetics | HLA-DRB1*15:01 is strongest genetic risk factor (OR ~3); >200 non-HLA susceptibility loci; MZ twins ~25–30%, DZ twins ~5% |
| Family risk | 15–20% have affected relative; first-degree relatives 10–20× risk; both parents with MS → ~30% risk to children |
- EBV seroconversion → 32-fold increased MS risk (Bjornevik et al., Science 2022) — MS risk is negligible in EBV-seronegative individuals
- HLA-DRB1*15:01 is the single strongest genetic risk factor for MS — chromosome 6
- Migration before age 15 = adopt new risk — suggests environmental exposure during adolescence is critical
- Monozygotic twin concordance is only ~25–30% — genetics important but NOT sufficient
Pathophysiology
Immunopathogenesis
| Immune Component | Role in MS |
|---|
| CD4+ T cells (Th1/Th17) | Cross BBB → recognize myelin antigens via MHC class II → release IFN-γ, IL-17 → activate macrophages |
| CD8+ T cells | Most abundant T cells in MS lesions; direct cytotoxic damage to oligodendrocytes and axons |
| B cells | Antigen presentation, cytokine production, intrathecal antibody secretion (OCBs); anti-CD20 therapy efficacy confirms B-cell centrality |
| Macrophages/microglia | Phagocytose myelin; release reactive oxygen species; drive slowly expanding lesions in progressive MS |
| Complement | Deposition in active lesions (Lassmann/Lucchinetti Pattern II pathology); contributes to demyelination |
| Astrocytes | Gliotic scar formation in chronic lesions; impede remyelination; contribute to BBB dysfunction |
Neuropathology
- 5 pathologic criteria for demyelination: (1) myelin sheath destruction, (2) relative axonal sparing, (3) perivascular inflammatory infiltrate, (4) perivenular white matter distribution, (5) reactive astrogliosis with relative paucity of Wallerian degeneration in acute lesions
- Demyelinating plaques: pink-gray lesions; perivenular distribution; primarily white matter but gray matter commonly affected
- Favored locations: periventricular white matter, optic nerves/chiasm, spinal cord, brainstem, cerebellar peduncles
- Dawson’s fingers: perivenular demyelination perpendicular to corpus callosum at the callosal–septal interface
- Axonal loss: significant even early in disease and in normal-appearing white matter — not purely demyelinating
- Gray matter pathology: cortical demyelination is common; subpial (Type III) and pan-cortical (Type IV) lesions are highly MS-specific and not seen in other demyelinating disorders
- Lesions do NOT extend beyond root entry zones of cranial or spinal nerves
Lesion Types
| Lesion Type | Description | Significance |
|---|
| Active/acute plaques | Dense macrophage infiltration, Gd enhancement | Correspond to clinical relapses |
| Chronic active (slowly expanding) | Rim of activated microglia at edge; smoldering inflammation | Drive silent progression; paramagnetic rim lesions (PRLs) on MRI |
| Chronic inactive | Demyelinated, gliotic, no active inflammation | “Burned out” lesions |
| Shadow plaques | Partial remyelination (thin myelin sheaths) | Evidence of attempted repair |
Physiologic Effects of Demyelination
- Loss of saltatory conduction → slowed or blocked signal transmission
- Uhthoff phenomenon: transient worsening (classically visual blurring) with increased temperature — 0.5°C rise can block conduction in demyelinated fibers
- Lhermitte sign: electric-like tingling down spine/limbs with neck flexion — cervical posterior column demyelination
- Heat, exercise, fever, hot baths, and smoking can all transiently worsen symptoms
- CD8+ T cells outnumber CD4+ T cells in MS lesions — a common board question
- Slowly expanding lesions (SELs) with paramagnetic rims drive disability in progressive MS — “smoldering MS”
- Dawson’s fingers = perivenular demyelination perpendicular to ventricles along callosal–septal interface
- MS is NOT purely demyelinating — significant axonal loss occurs early, even in normal-appearing white matter
Clinical Subtypes
MS Phenotypes
| Subtype | Frequency | Definition | Key Features |
|---|
| CIS | — | First clinical demyelinating event; does not yet fulfill DIT | 50–70% convert to MS within 20 years if brain MRI is abnormal; <25% if MRI is normal |
| RRMS | ~85% | Defined relapses with full or partial recovery; no progression between attacks | Most common at onset; ~0.5–1 relapse/year untreated; ~50% convert to SPMS within 15–20 years |
| SPMS | — | Initial RRMS followed by gradual progression ± superimposed relapses | Transition is insidious; confirmed retrospectively over 6–12 months of worsening |
| PPMS | 10–15% | Progressive decline from onset without early relapses | Equal M:F; older onset (~40–50); spinal cord predominant; fewer Gd-enhancing lesions; ocrelizumab only approved DMT |
Lublin 2014 Phenotypic Modifiers
| Modifier | Definition |
|---|
| Active | Clinical relapses AND/OR new/enlarging MRI lesions within past year |
| Not active | No relapses AND no new MRI activity |
| Progressing | Steadily increasing disability independent of relapses, confirmed over 6–12 months |
| Not progressing | Stable disability |
- Progressive-relapsing MS is no longer recognized — now classified as PPMS with activity
MS Variants
| Variant | Key Features |
|---|
| Marburg variant | Fulminant; rapid progression to stupor/coma/death over weeks–months; confluent large plaques; no remission |
| Baló concentric sclerosis | Alternating bands of demyelination and preserved myelin; concentric ring pattern on MRI |
| Schilder disease | Large bilateral hemispheric demyelination; children/young adults; high myelin basic protein |
| Tumefactive MS | Large (>2 cm) lesions mimicking tumor; open-ring enhancement (ring opens toward cortex) |
- CIS + abnormal brain MRI = high conversion risk — treat with DMT early; CIS with normal MRI has <25% conversion risk
- PPMS has equal M:F ratio — unlike RRMS (3:1 F:M); boards love this distinction
- Tumefactive MS: open-ring enhancement (ring opens toward cortex) = demyelination; closed ring = abscess or tumor
- Marburg variant: fulminant MS with rapid progression to death without remission
Classic Clinical Presentations
High-Yield Presentations
| Presentation | Key Features | Localization | Board Points |
|---|
| Optic neuritis |
Painful vision loss (worse with eye movement), central scotoma, dyschromatopsia, RAPD (Marcus Gunn pupil) detected by swinging flashlight test |
Optic nerve (retrobulbar > anterior) |
ONTT: IVMP 1 g/day × 3 days followed by oral prednisone 1 mg/kg × 11 days with rapid taper — speeds recovery but does NOT change final outcome; oral prednisone alone ↑ recurrence; 20–25% of initial MS presentations |
| INO |
Impaired adduction ipsilateral eye + abducting nystagmus contralateral eye |
MLF |
Bilateral INO is highly suggestive of MS (especially in young adults); unilateral INO in older patients is most often ischemic (small lacunar infarct of MLF) |
| One-and-a-half syndrome |
INO + ipsilateral horizontal gaze palsy — only abduction of contralateral eye remains |
MLF + ipsilateral PPRF or CN VI nucleus |
Think MS in young patient |
| Partial transverse myelitis |
Asymmetric motor/sensory deficits, bladder involvement, partial cord on MRI |
Spinal cord (cervical > thoracic) |
MS: short segment, partial, peripheral; partial myelitis predicts higher MS risk than complete myelitis |
| Lhermitte sign |
Electric shock down spine/limbs on neck flexion |
Cervical posterior columns |
Not specific to MS (cervical spondylosis, B12 deficiency, post-radiation) |
| Uhthoff phenomenon |
Transient worsening with heat/exercise |
Previously demyelinated pathways |
NOT a true relapse — temperature-dependent conduction block; no steroids needed |
| Trigeminal neuralgia |
Lancinating facial pain; may be bilateral |
Trigeminal root entry zone |
TN in patient <40, especially bilateral → suspect MS (~1% of MS patients) |
Symptoms of Established Disease
- Fatigue: most common symptom (~80%); amantadine, modafinil, and methylphenidate are widely used, but TRIUMPHANT-MS (Nourbakhsh, Lancet Neurol 2021) found no superiority over placebo — non-pharmacologic strategies (exercise, CBT) have stronger evidence
- Cognitive impairment: 40–65%; processing speed, memory, executive function; correlates with brain atrophy and cortical lesions
- Spasticity: baclofen (oral or intrathecal pump), tizanidine, botulinum toxin
- Bladder dysfunction: detrusor hyperreflexia (urgency/frequency) most common; PVR >100 mL → intermittent catheterization
- Walking impairment: dalfampridine (4-AP) 10 mg BID — blocks K+ channels; improves walking speed in ~35%; avoid if seizure history
- Neuropathic pain: dysesthesias, painful tonic spasms, trigeminal neuralgia
- Paroxysmal symptoms: brief stereotyped episodes (tonic spasms, dysarthria-ataxia) — respond to low-dose carbamazepine
- Charcot triad: nystagmus + scanning speech + intention tremor (advanced cerebellar disease)
- Seizures: 2–3% of MS patients
- Classic adage: MS presents with symptoms of one leg but signs in both
- Bilateral INO + young adult = MS; unilateral INO + elderly = brainstem stroke
- Best predictor of MS after optic neuritis: abnormal brain MRI at presentation
- Best predictor of MS after transverse myelitis: subclinical brain lesions on MRI at presentation
- Partial transverse myelitis predicts higher MS risk than complete myelitis
- Paroxysmal symptoms respond to low-dose carbamazepine — ephaptic transmission in demyelinated fibers
- Dalfampridine is the only FDA-approved drug specifically for MS walking impairment
McDonald Criteria 2017
Core Principle
- Diagnosis requires dissemination in space (DIS) + dissemination in time (DIT)
- Both can be satisfied clinically OR by MRI — no need to wait for second clinical attack
- Must exclude alternative diagnoses (no better explanation)
Dissemination in Space (DIS)
- ≥1 T2 lesion in ≥2 of 4 characteristic CNS regions:
| CNS Region | Notes |
|---|
| Periventricular | Most common location; Dawson fingers; ≥1 lesion required |
| Cortical/Juxtacortical | 2017 update: cortical lesions now count (not just juxtacortical); best on DIR sequences |
| Infratentorial | Brainstem, cerebellum, cerebellar peduncles |
| Spinal cord | Short-segment, peripheral, partial cross-section |
- 2017 update: symptomatic lesion CAN be used to fulfill DIS criteria (changed from 2010)
Dissemination in Time (DIT)
| DIT Criterion | Explanation |
|---|
| Simultaneous Gd+ and non-enhancing lesions | Both on a single MRI = lesions of different ages |
| New T2 or Gd+ lesion on follow-up MRI | Compared to baseline scan |
| CSF-specific oligoclonal bands | New in 2017: OCBs in CSF but not serum can substitute for DIT — allows earlier diagnosis |
Clinical Application
| Presentation | Additional Data Needed |
|---|
| ≥2 attacks + ≥2 objective lesions | None — DIS and DIT satisfied clinically |
| ≥2 attacks + 1 objective lesion | DIS by MRI OR second attack at different site |
| 1 attack + ≥2 objective lesions | DIT by MRI OR CSF OCBs OR second attack |
| 1 attack + 1 objective lesion (CIS) | DIS + DIT by MRI (or OCBs) OR second attack |
| Progressive from onset (PPMS) | ≥1 year progression PLUS ≥2 of: (1) ≥1 brain lesion in MS-typical region, (2) ≥2 spinal cord lesions, (3) CSF OCBs |
- CSF OCBs can replace DIT — the biggest change in McDonald 2017; DIS + OCBs = MS diagnosis at first presentation
- Cortical lesions now count for DIS — another 2017 update; previously only juxtacortical
- Symptomatic lesion counts for DIS in 2017 (could not in 2010)
- PPMS requires 1 year of progression + 2 of 3 (brain DIS, ≥2 cord lesions, positive CSF)
McDonald 2024 Revisions
| Update | Details |
|---|
| Optic nerve as 5th topographic region | Added to DIS criteria; demonstrated by VEP, OCT (retinal nerve fiber layer thinning), or MRI of the optic nerve |
| Central vein sign (CVS) | Supportive imaging biomarker; ≥6 lesions with CVS OR the "40% rule" (≥40% of lesions with central vein) supports MS diagnosis |
| Paramagnetic rim lesions (PRLs) | Susceptibility imaging biomarker of chronic active inflammation; supports MS diagnosis when present |
| CSF kappa free light chains (kFLC) | Accepted alongside OCBs as evidence of intrathecal immunoglobulin synthesis |
| DIT can be satisfied by biomarkers | At time of a single clinical or radiographic event, supportive biomarkers (OCBs/kFLC, CVS, PRLs) can substitute for DIT |
| RIS can be diagnosed as MS | If imaging meets DIS criteria PLUS supportive features (OCBs/kFLC, CVS, PRLs), MS can be diagnosed without a clinical event |
- Optic nerve is the 5th DIS region in McDonald 2024 — via VEP, OCT, or MRI
- CVS ≥6 lesions or 40% rule and PRLs are now formally supportive imaging biomarkers
- kFLC accepted alongside OCBs as evidence of intrathecal IgG synthesis
- RIS meeting DIS + biomarkers can be diagnosed as MS — no clinical event required
MRI Findings
Brain MRI
| Finding | Description | Significance |
|---|
| Dawson fingers | Ovoid T2/FLAIR hyperintensities perpendicular to ventricles along perivenular spaces | Most characteristic MS lesion; best seen on sagittal FLAIR |
| Corpus callosum lesions | T2 lesions at callosal-septal interface | Highly specific; unusual in small vessel disease or NMOSD |
| Open ring enhancement | Incomplete rim of Gd enhancement; open side faces gray matter | Specific for demyelination; closed ring = abscess or tumor |
| Central vein sign (CVS) | Central vein visible within lesion on T2*/SWI | ≥40% of lesions with central vein = MS; distinguishes from mimics |
| Paramagnetic rim lesion (PRL) | Dark rim on susceptibility imaging around chronic lesion | Chronic active/slowly expanding; iron-laden microglia; predicts faster disability |
| Cortical lesions | Within or abutting cortex; best on DIR sequences | Count for DIS (2017); correlate with cognitive decline |
| T1 black holes | Chronic T1 hypointensities | Represent axonal loss; correlate with disability better than T2 lesion load |
Spinal Cord MRI: MS vs NMOSD vs MOGAD
| Feature | MS | NMOSD | MOGAD |
|---|
| Length | Typically <2 vertebral segments and never longitudinally extensive (LETM = ≥3 segments rules out typical MS) | ≥3 segments (LETM) | ≥3 segments (LETM) |
| Cross-section | Partial, eccentric/peripheral | Central, ≥50% cross-section | Central gray matter involvement, often longitudinally extensive, with conus predilection |
| Location | Cervical > thoracic; dorsal/lateral | Cervical > thoracic; central | Thoracic > cervical; conus predilection |
- Open ring = demyelination; closed ring = abscess or tumor — open side faces gray matter
- Dawson fingers on sagittal FLAIR = single most recognizable MS MRI finding
- T1 black holes correlate with disability better than T2 lesion burden — represent irreversible axonal loss
- Central vein sign 40% rule: ≥40% lesions with central vein = MS; <40% = consider mimic
- MS cord lesions: short segment, partial, eccentric; NMOSD: longitudinally extensive, central
- Persistent Gd enhancement >2 months should raise concern for alternative diagnosis
CSF Analysis & Evoked Potentials
CSF Findings
| Test | Expected Finding | Clinical Significance |
|---|
| Oligoclonal bands (OCBs) | ≥2 bands in CSF not in serum | Present in 85–95%; can substitute for DIT (McDonald 2017); NOT specific (infections, sarcoidosis, SSPE) |
| IgG index | Elevated (>0.7) | Reflects intrathecal IgG synthesis; >1.7 highly suggestive |
| Cell count | Mild lymphocytic pleocytosis (<50) | >50 cells → consider alternative diagnosis |
| Protein | Normal or mildly elevated | >100 mg/dL suggests alternative diagnosis |
| Myelin basic protein | Elevated during relapses | Nonspecific; marker of active demyelination |
| Glucose | Normal | Low glucose = infection, sarcoidosis, NOT MS |
Evoked Potentials
| Test | Finding in MS | Key Points |
|---|
| Visual evoked potentials (VEP) | Prolonged P100 latency (>100 ms) | Most sensitive EP for MS (~80% in definite MS); detects subclinical optic neuritis; demyelination → prolonged latency |
| Somatosensory EP (SSEP) | Prolonged central conduction time | Detects subclinical cord/brainstem demyelination; ~69% in definite MS |
| Brainstem auditory EP (BAEP) | Prolonged interpeak latencies | Least sensitive for MS (~47%); detects pontine demyelination |
- OCBs must be CSF-specific — bands in BOTH serum and CSF = systemic immune activation, NOT intrathecal synthesis
- CSF pleocytosis >50 = not MS until proven otherwise — think NMOSD, infection, sarcoidosis
- OCBs persist for life regardless of treatment — compartmentalized intrathecal immune response
- Prolonged P100 on VEP = most commonly tested EP finding for MS on boards
- Demyelination = prolonged latency; axonal loss = reduced amplitude
Acute Relapse Management
Relapse Definition
- New or worsening symptoms lasting ≥24 hours, in absence of fever or infection, ≥30 days from prior relapse
- Pseudorelapse: worsening from UTI, fever, heat, stress — treat the trigger, NOT with steroids
Treatment
| Treatment | Regimen | Key Points |
|---|
| IV methylprednisolone | 1 g/day × 3–5 days | First-line; speeds recovery but does NOT alter long-term disability or prevent future relapses |
| High-dose oral methylprednisolone | 1000 mg/day PO (or equivalent) × 3–5 days | Non-inferior to IV (COPOUSEP trial, Le Page et al., Lancet 2015); alternative when IV impractical |
| Plasma exchange (PLEX) | 5–7 exchanges over 10–14 days | For steroid-refractory severe relapses; ~40% respond |
| ACTH gel | 80 units IM/SC daily × 5 days | Alternative to steroids; expensive; rarely first-line |
- IV methylprednisolone speeds recovery but does NOT change final outcome — classic ONTT finding
- Oral prednisone alone for optic neuritis is contraindicated — ONTT showed increased recurrence rate
- Always rule out pseudorelapse (UTI, infection, fever) before treating with steroids
- PLEX is reserved for severe, steroid-refractory relapses
Disease-Modifying Therapies (DMTs)
DMT Tiers
| Tier | Agents | Mechanism / Notes |
|---|
| Platform (modest efficacy) | Interferon-beta (IFN-β1a, IFN-β1b, pegylated IFN), glatiramer acetate, teriflunomide, dimethyl fumarate (DMF), diroximel fumarate (DRF) | Older, well-established safety; favored in mild disease or pregnancy planning (glatiramer, IFN-β) |
| Moderate-efficacy (S1P modulators) | Fingolimod, ozanimod, ponesimod, siponimod | Sequester lymphocytes in lymph nodes; first-dose cardiac monitoring (fingolimod); CYP2C9 genotyping required for siponimod; siponimod approved for active SPMS |
| High-efficacy | Anti-CD20 (ocrelizumab, ofatumumab, ublituximab, rituximab off-label); natalizumab; alemtuzumab; cladribine | Ocrelizumab is only DMT approved for PPMS; natalizumab carries PML risk (anti-JCV antibody index); alemtuzumab causes secondary autoimmunity (thyroid, ITP, anti-GBM) |
Treatment Paradigm
- Escalation approach: begin with platform DMT; escalate to higher-efficacy agents if breakthrough disease (relapses, new MRI activity, disability progression)
- Early aggressive approach: initiate high-efficacy DMT at diagnosis to prevent disability accrual — supported by observational data
- Ongoing head-to-head RCTs: TREAT-MS and DELIVER-MS comparing escalation vs early aggressive strategies
Key Safety Monitoring
| DMT | Monitoring |
|---|
| Natalizumab | Anti-JCV antibody index every 6 months — PML risk stratification (index >1.5 + duration >24 months + prior immunosuppression = highest risk) |
| S1P modulators (fingolimod, etc.) | Lymphocyte counts (PML reported); first-dose cardiac monitoring (bradycardia, AV block); macular edema screening; VZV serology pre-treatment. Abrupt cessation of fingolimod (or natalizumab) can precipitate severe rebound demyelinating disease within 3–6 months — fulminant relapse(s) sometimes worse than baseline; treat with high-dose steroids ± PLEX, and bridge to next DMT promptly. Do NOT stop without a transition plan. |
| Dimethyl/diroximel fumarate | Absolute lymphocyte count — PML risk in prolonged lymphopenia (<500/mm³) |
| Siponimod | CYP2C9 genotyping required before initiation (dose-adjusted or contraindicated) |
| Alemtuzumab | Monthly CBC, creatinine, urinalysis, thyroid function for 48 months after last dose — secondary autoimmunity (thyroid, ITP, anti-GBM) |
| Anti-CD20 (ocrelizumab, ofatumumab, ublituximab) | Hepatitis B screening; immunoglobulin levels; infection vigilance (hypogammaglobulinemia with prolonged use) |
| Cladribine | Lymphocyte counts; malignancy surveillance; herpes zoster prophylaxis |
Autologous Hematopoietic Stem Cell Transplantation (aHSCT)
- Option for highly active RRMS refractory to high-efficacy DMTs
- MIST trial (Burt et al., JAMA 2019): aHSCT superior to DMT for disease progression and relapse rate in selected patients
- Significant procedural risk (infection, infertility, secondary autoimmunity, treatment-related mortality)
- Should be performed only at experienced centers with appropriate patient selection
- Ocrelizumab is the only DMT approved for PPMS
- Siponimod is approved for active SPMS — requires CYP2C9 genotyping
- Natalizumab + JCV+ + >24 months + prior immunosuppression = highest PML risk
- Alemtuzumab triad of secondary autoimmunity: thyroid disease, ITP, anti-GBM nephritis — monitor monthly for 48 months
- aHSCT (MIST trial) — consider for highly active RRMS refractory to high-efficacy DMT
Symptomatic Management
Pseudobulbar Affect (PBA)
- Involuntary, exaggerated laughing or crying incongruent with mood
- Dextromethorphan/quinidine (Nuedexta) — FDA-approved for PBA
- SSRIs and TCAs — effective alternatives
Depression in MS
- Lifetime prevalence ~50% — substantially higher than the general population
- Increased suicide risk in MS — screen routinely (PHQ-9 or similar)
- First-line: SSRIs or SNRIs; combine with CBT when available
Bladder Management
| Pattern | Treatment |
|---|
| Detrusor overactivity (urgency/frequency) | Antimuscarinics: oxybutynin, tolterodine, solifenacin; mirabegron (β3 agonist) as alternative when anticholinergic burden is a concern |
| Refractory detrusor overactivity | Intradetrusor onabotulinumtoxinA injections |
| Detrusor-sphincter dyssynergia / retention | Clean intermittent catheterization if PVR >100 mL; alpha-blockers (tamsulosin) may help functional outlet obstruction |
- Dextromethorphan/quinidine (Nuedexta) = FDA-approved for PBA
- ~50% of MS patients develop depression — screen routinely; SSRIs/SNRIs first-line
- Mirabegron is a β3-agonist alternative to antimuscarinics for detrusor overactivity
- Intradetrusor onabotulinumtoxinA for refractory neurogenic detrusor overactivity
Prognostic Factors
Favorable vs Unfavorable
| Favorable Prognosis | Unfavorable Prognosis |
|---|
| Young age at onset | Older age at onset (>40) |
| Female sex | Male sex |
| Optic neuritis or sensory onset | Motor or cerebellar onset |
| Complete recovery from first relapse | Incomplete recovery from first relapse |
| Low T2 lesion burden on initial MRI | High T2 lesion burden; T1 black holes |
| Long interval between first and second relapse | Short inter-relapse interval; frequent early relapses |
| RRMS phenotype | Progressive course from onset (PPMS) |
| Minimal disability at 5 years | Early brain atrophy; spinal cord/brainstem lesions |
- Cerebellar ataxia at onset predicts poor prognosis without significant remission
- Optic neuritis and sensory onset = most favorable presenting features
- Best early predictor of long-term disability: degree of recovery from first relapse
- T1 black holes on MRI represent irreversible axonal loss and correlate with disability
Special Situations
MS and Pregnancy
| Period | Relapse Rate | Key Points |
|---|
| 1st–2nd trimester | Decreased | Immunomodulatory state of pregnancy is protective |
| 3rd trimester | Lowest (~70% reduction) | Shift toward Th2 immune response |
| Postpartum (first 3 months) | Increased (rebound) | 20–40% relapse rate; consider resuming DMT immediately postpartum |
- Pregnancy does NOT worsen long-term MS prognosis
- Glatiramer acetate and interferon-beta have the most reassuring pregnancy experience among MS DMTs and may be continued through conception or pregnancy in selected patients after a clear risk-benefit discussion (EMA label updated 2019; no washout required for either). Most other DMTs are stopped before conception per individual label guidance.
- Teriflunomide: contraindicated in pregnancy and in females of reproductive potential not using effective contraception (FDA pregnancy letter categories were retired in 2015 with the PLLR; "Category X" is historical shorthand); perform accelerated elimination with cholestyramine or activated charcoal if pregnancy occurs or rapid drug clearance is needed (drug otherwise persists up to 2 years).
- Acute relapse in pregnancy: IV methylprednisolone can be used (avoid 1st trimester if possible)
Pediatric MS
- Onset before age 18 in ~3–5% of MS patients; almost exclusively RRMS
- Higher relapse rate than adult MS but better relapse recovery
- Must distinguish from ADEM: ADEM = monophasic, encephalopathy required, bilateral; MS = relapsing, no encephalopathy
- MOG antibodies more common in pediatric patients — test MOG-IgG in all pediatric demyelinating events
- Fingolimod: FDA-approved for pediatric MS (age ≥10; PARADIGMS trial)
Radiologically Isolated Syndrome (RIS)
- Incidental MRI findings meeting DIS criteria without clinical symptoms
- ~34% develop a clinical event within 5 years; ~50% within 10 years
- Highest conversion risk: spinal cord lesions, age <37, male, positive OCBs, Gd-enhancing lesions
- ARISE trial: dimethyl fumarate reduced time to first clinical event in RIS — first RCT for DMT in RIS
- Relapse rate ↓ in 3rd trimester, ↑ postpartum — among most commonly tested MS facts
- Pediatric MS vs ADEM: ADEM = monophasic + encephalopathy; MS = relapsing, no encephalopathy
- RIS with spinal cord lesions = highest conversion risk — may benefit from early DMT
- Fingolimod is FDA-approved for pediatric MS (age ≥10; PARADIGMS trial)
Differential Diagnosis
Key MS Mimics
| Category | Conditions | Distinguishing Features |
|---|
| Demyelinating | NMOSD, MOGAD, ADEM | NMOSD: AQP4+, LETM, area postrema; MOGAD: MOG+, bilateral ON; ADEM: monophasic, encephalopathy |
| Autoimmune | SLE, Sjögren, Behçet, sarcoidosis | Systemic features; specific serologies; leptomeningeal enhancement in sarcoidosis |
| Vascular | CNS vasculitis, CADASIL, microvascular disease | CADASIL: anterior temporal + external capsule WML; microvascular: older age, no enhancement |
| Infectious | HIV, HTLV-1, Lyme, syphilis, PML | PML: JC virus, no enhancement, subcortical U-fibers |
| Metabolic | B12 deficiency, copper deficiency | Posterior column + corticospinal without brain lesions |
| Genetic | Adrenoleukodystrophy, leukodystrophies | VLCFA for ALD; symmetric confluent WM changes |
Red Flags Suggesting Alternative Diagnosis
- CSF protein >100 mg/dL or pleocytosis >50 cells
- Persistent Gd enhancement >2 months
- Longitudinally extensive cord lesions (≥3 segments)
- Bilateral simultaneous optic neuritis
- Absence of oligoclonal bands
- Prominent encephalopathy or seizures at onset
- Systemic inflammatory symptoms (rash, oral ulcers, uveitis)
- Intractable nausea, vomiting, or hiccups (area postrema syndrome → NMOSD)
- Always check VLCFA in young men with progressive myelopathy and white matter changes — rule out adrenomyeloneuropathy/ALD
- CADASIL: anterior temporal + external capsule WML in young patient with migraine and strokes — NOTCH3 mutation
- Minimum workup to exclude mimics: CBC, CMP, ESR, ANA, B12, RPR, TSH; MRI brain + spine with contrast
References
- Thompson AJ, Banwell BL, Barkhof F, et al. Diagnosis of multiple sclerosis: 2017 revisions of the McDonald criteria. Lancet Neurol. 2018;17(2):162-173.
- Lublin FD, Reingold SC, Cohen JA, et al. Defining the clinical course of multiple sclerosis: the 2013 revisions. Neurology. 2014;83(3):278-286.
- Bjornevik K, Cortese M, Healy BC, et al. Longitudinal analysis reveals high prevalence of Epstein-Barr virus associated with multiple sclerosis. Science. 2022;375(6578):296-301.
- Filippi M, Bar-Or A, Piehl F, et al. Multiple sclerosis. Nat Rev Dis Primers. 2018;4(1):43.
- Optic Neuritis Study Group. Visual function 15 years after optic neuritis. Ophthalmology. 2008;115(6):1079-1082.
- Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor’s Principles of Neurology. 12th ed. McGraw-Hill; 2023.
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