Multiple sclerosis from basics for INICET
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I now have comprehensive information from multiple authoritative sources. Let me compile the full INICET-focused notes on Multiple Sclerosis.
Multiple Sclerosis (MS) - Complete INICET Review
1. DEFINITION & OVERVIEW
Multiple sclerosis is a chronic, inflammatory, demyelinating, and neurodegenerative disease of the CNS, characterized by lesions ("plaques") separated in time and space. It is the most common cause of non-traumatic neurological disability in young adults in developed countries.
- Worldwide prevalence: ~2.8 million; ~309/100,000 in adult US population
- Sex ratio: Women > Men (2-2.5:1) - typical of autoimmune disease
- Age of onset: 3rd-4th decade (range: post-pubertal teenagers to 50s)
- Geography: Higher prevalence in temperate latitudes (approaching 1/500 in some areas); less common near the equator (1/20,000)
2. CLASSIFICATION OF CLINICAL SUBTYPES
| Type | Description |
|---|---|
| Relapsing-Remitting MS (RRMS) | Most common (~85% at onset). Discrete attacks with full or partial recovery |
| Secondary Progressive MS (SPMS) | Initially RRMS, then converts to a steady progressive course (often 10-20 yrs later) |
| Primary Progressive MS (PPMS) | Steady progression from onset, no clear relapses; occurs in older patients (>40 yrs); ~15% of MS |
| Clinically Isolated Syndrome (CIS) | Single demyelinating episode - may or may not evolve into MS |
| Marburg Disease | Acute, fulminant, rapidly fatal variant |
| Tumefactive MS | Large demyelinating lesion mimicking a tumour |
| Balo's Concentric Sclerosis | Concentric rings of demyelination and preserved myelin |
| Schilder Disease | Diffuse cerebral sclerosis |
3. ETIOLOGY & RISK FACTORS
Genetic Factors
- Monozygotic twin concordance: 15-50% (not 100% - confirms environmental role)
- Dizygotic twin concordance: 3-5%
- First-degree relative risk: 2-4% (vs. 0.1% general population)
- HLA-DRB1*1501 (HLA-DR2 haplotype) - most strongly associated; chromosome 6p21 (MHC class II)
- IL-2 receptor-α and IL-7 receptor-α gene SNPs also implicated
- Overlap with other autoimmune diseases: rheumatoid arthritis, SLE, autoimmune thyroid disease, IBD
Environmental/Acquired Factors
- Vitamin D deficiency - low vitamin D / less sunlight exposure increases risk
- EBV infection - molecular mimicry proposed
- Cigarette smoking and childhood obesity - increased risk
- Faroe Islands epidemic - documented post-WWII, supports environmental trigger
- Gut dysbiosis (Akkermansia muciniphila association)
4. PATHOLOGY & PATHOPHYSIOLOGY
The Plaque (Core Lesion)
- Macroscopic: Grey-pink depressed areas in white matter, below cut surface
- Microscopic (active plaque):
- Perivascular infiltration of T-cells and macrophages
- Myelin stripping by activated macrophages
- Relative preservation of axons (in early disease)
- Oligodendrocyte loss
- Chronic plaque: Gliosis (astrocytic scarring), reduced axon density, remyelination (shadow plaques)
Predilection Sites (HIGH YIELD)
- Periventricular white matter (especially at angles of lateral ventricles - "Dawson's fingers" on MRI)
- Corpus callosum (undersurface - "Dawson's fingers" on sagittal MRI)
- Optic nerves (causing optic neuritis)
- Brainstem (MLF - internuclear ophthalmoplegia)
- Cervical spinal cord (dorsolateral columns)
- Cerebellar peduncles
- Juxtacortical white matter
- Cortical gray matter (increasingly recognized)
Immunopathogenesis
- Autoreactive CD4+ T-helper cells (TH1 subtype) are sensitized to myelin antigens (mainly Myelin Basic Protein - MBP) - likely via molecular mimicry with EBV or other antigens
- These T-cells cross the BBB, get re-activated by local antigen-presenting cells
- TH1 cytokines (IFN-γ, TNF-α, IL-2) - activate macrophages and damage oligodendrocytes/myelin
- CD8+ cytotoxic T-cells found at active edges of expanding plaques
- B-cells - important as antigen-presenting cells; high producers of TNF-α
- Microglial activation - hallmark of progressive MS
- Experimental model: EAE (Experimental Allergic Encephalomyelitis)
Conduction Physiology
- Normal: Saltatory conduction node-to-node (~70 m/s)
- Demyelination: Conduction block (exposed K+ channels → hyperpolarization)
- Recovery: Na+ channels redistribute along the naked axon → continuous (slow) conduction restored
- Temperature sensitivity: Heat (Uhthoff phenomenon) worsens conduction in partially demyelinated axons
- Uhthoff's phenomenon: Worsening of symptoms with heat (fever, exercise, hot bath)
5. CLINICAL FEATURES (HIGH YIELD)
Common Presenting Symptoms
| Symptom | Detail |
|---|---|
| Optic neuritis | Most common first symptom - unilateral painful visual loss, RAPD, colour desaturation; typically recovers |
| Sensory disturbances | Paresthesias, numbness - most common overall symptom |
| Limb weakness | Mono/paraparesis; UMN signs (spasticity, hyperreflexia, extensor plantar) |
| Cerebellar signs | Charcot's triad: Intention tremor + Nystagmus + Scanning/staccato speech (dysarthria) |
| Diplopia/INO | Internuclear ophthalmoplegia (MLF lesion) - pathognomonic of MS in young adults |
| Bladder dysfunction | Urgency, frequency, hesitancy, incontinence (most common autonomic symptom) |
| Lhermitte's sign | Electric shock-like sensation down the back/limbs on neck flexion (posterior column lesion in cervical cord) |
| Fatigue | Very common, often disabling; treated with amantadine or modafinil |
| Depression/cognitive changes | Part of disease itself, not just a reaction |
Classic Eponymous Signs
- Lhermitte's sign: Neck flexion → electric shock sensation down spine/limbs
- Uhthoff's phenomenon: Worsening with heat
- Pulfrich effect: Misperception of moving objects due to different conduction velocities in the two optic nerves
- Charcot's triad: Intention tremor + nystagmus + scanning speech (cerebellar disease in MS)
- INO (Internuclear Ophthalmoplegia): MLF lesion - adduction palsy ipsilateral eye + nystagmus contralateral eye; bilateral INO in young adult = MS until proven otherwise
Paroxysmal Symptoms
- Short, stereotyped attacks lasting seconds to minutes (many times/day)
- Tonic spasms, paroxysmal dysarthria/ataxia, pain, Lhermitte's
- Triggered by sensory stimuli or hyperventilation
- Mechanism: Ephaptic transmission between demyelinated axons
- Treatment: Carbamazepine (most effective); acetazolamide for hyperventilation-induced tonic spasms
Important Negatives (Unusual in MS)
- Bell's palsy (peripheral facial nerve) - rarely seen in MS
- Seizures - uncommon (but do occur)
6. DIAGNOSIS
McDonald Criteria (2017 Revision) - KEY EXAM TOPIC
The diagnosis requires demonstration of Dissemination in Space (DIS) AND Dissemination in Time (DIT):
| Clinical Presentation | Additional Data Required |
|---|---|
| ≥2 attacks + ≥2 objective lesions | None (clinical diagnosis) |
| ≥2 attacks + 1 objective lesion | DIS by MRI, or 2nd attack in different location |
| 1 attack + ≥2 objective lesions | DIT by MRI, or CSF OCBs, or 2nd attack |
| 1 attack + 1 objective lesion (CIS) | DIS by MRI + DIT by MRI/CSF OCBs/2nd attack |
| Progressive from onset (PPMS) | ≥1 year progression + ≥2 of: brain T2 lesions, ≥2 spinal T2 lesions, CSF OCBs |
MRI Criteria (2017)
DIS (Dissemination in Space): ≥1 T2 lesion in at least 2 of 4 areas:
- Periventricular
- Cortical or juxtacortical
- Infratentorial (posterior fossa/brainstem/cerebellum)
- Spinal cord
DIT (Dissemination in Time): Either:
- Simultaneous gadolinium-enhancing AND non-enhancing lesions (different ages), OR
- New T2/gadolinium lesion on follow-up MRI
MRI Findings
- T2/FLAIR: Hyperintense plaques (white) in periventricular/juxtacortical regions
- Dawson's Fingers: Periventricular lesions perpendicular to lateral ventricles on sagittal FLAIR (along medullary veins)
- T1 "Black Holes": Chronic lesions with irreversible axonal loss
- Gadolinium enhancement: Active inflammation/BBB breakdown (lasts ~4-8 weeks per lesion)
- Cortical atrophy: In advanced disease
CSF Findings (HIGH YIELD)
| Finding | Detail |
|---|---|
| Oligoclonal bands (OCBs) | Present in >95% of MS (most sensitive CSF test); 2 or more bands in CSF but NOT in serum (intrathecal IgG synthesis) |
| IgG index | Elevated (>0.7) |
| Mild lymphocytic pleocytosis | Usually <50 cells |
| Myelin basic protein | May be elevated during acute attack |
| Opening pressure, glucose | Normal |
Evoked Potentials
- Visual Evoked Potentials (VEP): Prolonged P100 latency (delayed, not absent) - even in subclinical optic neuritis - very useful to detect clinically silent lesions
- SSEP, BAEP: Also used
7. DIFFERENTIAL DIAGNOSIS (High Yield)
| Condition | Distinguishing Feature |
|---|---|
| Neuromyelitis Optica (Devic's) | Bilateral severe optic neuritis + longitudinally extensive transverse myelitis (≥3 vertebral segments); AQP4-IgG (anti-NMO) or MOG-IgG positive; NOT periventricular lesions on MRI |
| ADEM | Monophasic; children; follows infection/vaccination; diffuse bilateral lesions; encephalopathy |
| Vitamin B12 deficiency | Subacute combined degeneration; no OCBs; megaloblastic anemia |
| CNS Vasculitis/SLE | Serological markers |
| Sarcoidosis | Hilar lymphadenopathy; ACE elevated |
| HIV/HTLV myelopathy | Serology |
8. TREATMENT
A. Acute Relapse Treatment
First-line: IV methylprednisolone 1g/day for 3-5 days (shortens duration, does NOT change long-term outcome)
- Followed by optional oral prednisone taper (60-80 mg tapering over 12-20 days)
- Note: Optic Neuritis Treatment Trial (ONTT): Oral prednisone ALONE slightly increased risk of new optic neuritis episodes - avoid oral steroids alone
Second-line (severe/steroid-resistant): Plasma exchange (PLEX); IV immunoglobulin
B. Disease-Modifying Therapies (DMTs) - HIGH YIELD
Injectables
| Drug | Mechanism | Notes |
|---|---|---|
| Interferon beta-1a (Avonex, Rebif) | Immunomodulation; reduces BBB breakdown, alters cytokine profile | SE: flu-like symptoms, injection site reactions, hepatotoxicity, depression |
| Interferon beta-1b (Betaseron) | Same as above | Same SEs |
| Glatiramer acetate (Copaxone) | Synthetic myelin-like polypeptide (decoy for T-cell attack) | SE: post-injection flushing, chest tightness, anxiety (self-limiting) |
Oral Agents
| Drug | Mechanism | Key Side Effects |
|---|---|---|
| Fingolimod (Gilenya) | S1P receptor modulator → sequesters lymphocytes in lymph nodes | First-dose bradycardia (monitor 6 hrs), macular edema, PML risk |
| Teriflunomide (Aubagio) | Inhibits pyrimidine synthesis (DHODH inhibitor) | Teratogenic; liver toxicity; monitor LFTs |
| Dimethyl fumarate (Tecfidera) | Activates Nrf2 pathway (anti-inflammatory) | Flushing, GI upset, lymphopenia, PML risk |
| Siponimod (Mayzent) | Selective S1P1/5 modulator | For SPMS; CYP2C9 polymorphism testing required |
| Ozanimod (Zeposia) | S1P1/5 modulator | CYP2C8 interactions |
| Cladribine (Mavenclad) | Purine nucleoside analogue; lymphocyte depletion | Oral; lymphopenia; teratogenic |
Monoclonal Antibodies (High Efficacy)
| Drug | Target | Key Points |
|---|---|---|
| Natalizumab (Tysabri) | Anti-α4 integrin (VLA-4) → blocks lymphocyte migration across BBB | High efficacy; major risk: PML (due to JC virus reactivation); check JCV antibody index before use |
| Ocrelizumab (Ocrevus) | Anti-CD20 (B-cell depletion) | Only drug approved for PPMS; SE: infusion reactions, PML risk, increased infection risk |
| Ofatumumab (Kesimpta) | Anti-CD20 (subcutaneous) | Self-injectable; RRMS |
| Alemtuzumab (Lemtrada) | Anti-CD52 | Very high efficacy; SE: secondary autoimmunity (ITP, thyroid disease, Goodpasture syndrome) |
C. Symptomatic Treatment
| Symptom | Treatment |
|---|---|
| Spasticity | Baclofen (GABA-B agonist), tizanidine, diazepam; intrathecal baclofen for severe cases |
| Fatigue | Amantadine, modafinil, 4-aminopyridine (dalfampridine) |
| Bladder dysfunction | Anticholinergics (oxybutynin) for overactive bladder; intermittent catheterization |
| Neuropathic pain | Gabapentin, pregabalin, carbamazepine |
| Depression | SSRIs |
| Paroxysmal symptoms | Carbamazepine, acetazolamide |
| Walking speed | Dalfampridine (Ampyra) - K+ channel blocker; improves conduction in demyelinated axons |
| Sexual dysfunction | PDE-5 inhibitors (sildenafil) |
9. PROGNOSTIC FACTORS
Better Prognosis
- Young age at onset
- Female sex
- Sensory/visual onset (vs. motor)
- Complete recovery from first attack
- Long interval between first and second attack
- Low lesion load on initial MRI
Worse Prognosis
- Male sex
- Age >40 at onset (more likely PPMS)
- Motor or cerebellar onset
- Short interval between first two attacks
- High T2 lesion load on initial MRI
- "Black holes" (T1 hypointense lesions)
10. SPECIAL EXAM-RELEVANT ASSOCIATIONS
| Point | Fact |
|---|---|
| MS + pregnancy | Relapse rate decreases during pregnancy (especially 3rd trimester); increases post-partum |
| Tic douloureux in young patient | Always think MS |
| Bilateral INO in young adult | MS until proven otherwise |
| Clinically isolated syndrome (CIS) | First demyelinating event; 50-70% convert to MS within 10 years |
| ONTT | Oral steroids alone contraindicated for optic neuritis (increases recurrence) |
| Most sensitive CSF finding | Oligoclonal bands (>95% sensitivity) |
| MRI finding most specific for MS | Dawson's fingers (periventricular lesions perpendicular to ventricles on sagittal FLAIR) |
| Experimental model | EAE (Experimental Allergic Encephalomyelitis) |
| Only approved drug for PPMS | Ocrelizumab (anti-CD20) |
| Drug causing first-dose bradycardia | Fingolimod (requires 6-hour ECG monitoring after first dose) |
| Risk of PML | Natalizumab (highest), fingolimod, dimethyl fumarate, ocrelizumab |
| Uhthoff's phenomenon | Heat worsens symptoms (K+ channel exposure) |
| Lhermitte's sign | Cervical cord lesion (posterior columns) |
11. NEUROMYELITIS OPTICA (NMO) vs MS - QUICK COMPARISON (INICET TRAP)
| Feature | MS | NMO (Devic's) |
|---|---|---|
| Antibody | None specific | AQP4-IgG (anti-NMO), or MOG-IgG |
| Optic neuritis | Unilateral, mild | Bilateral, severe, simultaneous |
| Myelitis extent | Short (<3 segments) | Longitudinally extensive (≥3 segments) |
| MRI brain | Periventricular lesions | Often normal |
| CSF OCBs | >95% | Rare |
| Treatment | DMTs (see above) | Rituximab, immunosuppressants (NOT interferons - can worsen NMO) |
Sources: Adams and Victor's Principles of Neurology 12e | Goldman-Cecil Medicine | Harrison's Principles of Internal Medicine 22e | Lippincott Illustrated Reviews Pharmacology
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