Multiple sclerosis is a chronic autoimmune demyelinating disease of the central nervous system characterized by spatially and temporally disseminated inflammatory plaques in the brain and spinal cord, leading to varied neurological deficits.

Multiple Sclerosis (MS)

Multiple sclerosis (MS) is an idiopathic inflammatory demyelinating disorder of the CNS ^[1]. The name itself tells you the disease: "multiple" = many, "sclerosis" = hardening/scarring — referring to the multiple hardened (sclerosed) plaques of demyelination scattered throughout the brain and spinal cord.

It is a chronic inflammatory demyelinating neurodegenerative disease in young adults, characterised by multiple plaques of demyelination in the CNS with dissemination in space and time ^[2]. This "dissemination in space AND time" concept is absolutely central — it means:

Space: Lesions occur in multiple, anatomically distinct locations within the CNS
Time: Lesions occur at different time points (i.e., not a single monophasic event)

Key Conceptual Point

Demyelination of the PNS is NOT considered MS by definition ^[3]. MS is exclusively a CNS disease. If you see PNS demyelination (e.g., GBS), that's a completely different entity. The CNS includes the brain, spinal cord, and optic nerves (cranial nerve II is technically a CNS tract, not a true peripheral nerve — it is ensheathed by oligodendrocytes, not Schwann cells).

MS is an important cause of non-traumatic disability in young adults (18–40 yr) ^[1]. This is a critical exam point — in a young adult presenting with episodic neurological deficits that come and go, MS should be at the top of your differential.

2. Epidemiology

Prevalence varies enormously by geography: 5 per 100,000 (lowest, Western Pacific) to 111–300 per 100,000 (highest, Europe & Americas) ^[1]
~2.8 million patients worldwide ^[1]
There is a well-established latitude gradient: prevalence increases with distance from the equator (both north and south). This is thought to relate to sunlight exposure and vitamin D synthesis — populations closer to the equator get more UV-B radiation → more vitamin D → potentially lower MS risk.

Prevalence in Hong Kong: ~1/1000 (i.e., ~5–10 per 100,000) ^[2] — much lower than Western countries but not negligible
MS was historically considered rare in Asian populations, but incidence is rising, possibly due to improved diagnosis and changing environmental/lifestyle factors
In Asian MS patients, there is a higher proportion of opticospinal MS (predominantly affecting optic nerves and spinal cord) — some of these may overlap with or actually be NMOSD (neuromyelitis optica spectrum disorder), which is relatively more common in Asian populations

Female predominance: F:M = 3:1 ^[1]^[4]
Mean age at diagnosis ~32 years ^[1]
Age of onset between 15–50 is suggestive of MS ^[3]
The female predominance is typical of autoimmune diseases and may relate to hormonal influences on immune regulation (oestrogen tends to promote Th1/Th17 responses)

High Yield: If a question describes a young woman (20s–30s) with episodic neurological symptoms affecting different CNS regions at different times, think MS immediately.

3% risk if first-degree relative affected (lower in Asians) ^[4]
Monozygotic twin concordance ~30% ^[4] — this tells you genetics matter but aren't the whole story (if it were purely genetic, concordance would be ~100%)

3. Anatomy and Function (Relevant to MS)

To understand MS, you need to understand what myelin does and where the lesions occur.

Myelin is a lipid-rich insulating sheath wrapped around axons, produced by oligodendrocytes in the CNS (vs. Schwann cells in the PNS)
One oligodendrocyte myelinates multiple axons (up to 50), whereas one Schwann cell myelinates only one internode of one axon — this is why CNS demyelination can be so devastating
Myelin enables saltatory conduction: action potentials "jump" between Nodes of Ranvier, dramatically increasing conduction velocity (from ~1 m/s unmyelinated to ~100 m/s myelinated)
When myelin is damaged, conduction slows, becomes unreliable, or fails entirely — producing neurological deficits

MS plaques have a characteristic predilection for perivenular white matter (because the inflammatory process begins around small veins). Key sites include:

Site	Frequency	Key Structures Affected
Optic nerve	~1/3 of presentations ^[2]	CN II (technically CNS tissue)
Brainstem	~1/3 of presentations ^[2]	MLF (medial longitudinal fasciculus), cranial nerve nuclei, cerebellar peduncles
Spinal cord	~1/3 of presentations ^[2]	Corticospinal tracts, dorsal columns, spinothalamic tracts
Periventricular white matter	Very common on MRI	Adjacent to lateral ventricles ("Dawson's fingers")
Cerebellum	Common	Cerebellar peduncles and white matter
Corpus callosum	Characteristic	Callosal-septal interface
Cortical grey matter	Increasingly recognised ^[2]	Cortical lesions, brain atrophy

Why Periventricular?

MS plaques cluster around small veins (venules) that drain into the lateral ventricles. The inflammatory cells in MS cross the blood-brain barrier at these venular sites. On MRI, this creates the classic "Dawson's fingers" — periventricular lesions oriented perpendicular to the ventricles, following the path of the medullary veins.

Corticospinal tract (lateral column of spinal cord): upper motor neuron signs — spastic weakness, hyperreflexia, Babinski sign
Dorsal columns (DCML): proprioception, vibration, fine touch — sensory ataxia, Romberg's sign positive
Spinothalamic tract (STT): pain and temperature — paraesthesia, hypaesthesia
Medial longitudinal fasciculus (MLF) in brainstem: coordinates conjugate eye movements — internuclear ophthalmoplegia (INO) when damaged
Cerebellar connections: coordination — ataxia, intention tremor, dysmetria, dysdiadochokinesia, scanning speech

4. Aetiology and Risk Factors

Aetiologies include: genetic susceptibility, environmental factors (e.g. EBV), and lifestyle factors ^[1]. MS is a multifactorial disease — no single cause, but a combination of genetic predisposition and environmental triggers.

HLA-DRB115:01 gene* is the strongest genetic risk factor ^[2] — this is an MHC class II allele involved in antigen presentation to CD4+ T cells. It makes sense: if you have an HLA allele that is particularly good at presenting self-myelin antigens, autoreactive T cells are more likely to be activated.
Other associated genes: CLEC16 (autophagy regulation), IL receptor genes (IL-2R, IL-7R — T cell homeostasis), CD226 (T cell co-stimulation) ^[4]
Polygenic: over 200 genetic loci associated with MS risk, most relating to immune function
Inheritance: NOT Mendelian; complex polygenic with environmental interaction

Factor	Mechanism	Evidence
Epstein-Barr Virus (EBV) ^[1]^[2]^[4]	Molecular mimicry between EBV antigens (e.g., EBNA-1) and myelin antigens (e.g., GlialCAM); EBV also infects B cells, potentially driving chronic immune activation in the CNS	Landmark 2022 Science paper (Bjornevik et al.) showed 32× increased risk after EBV infection; virtually all MS patients are EBV seropositive
Reduced vitamin D / sunlight exposure ^[2]^[4]	Vitamin D has immunomodulatory effects — promotes Treg cells, suppresses Th1/Th17 responses; UV-B also has direct immunosuppressive effects independent of vitamin D	Latitude gradient; vitamin D deficiency associated with higher MS risk and more relapses
HHV-6 ^[2]	Possible molecular mimicry; HHV-6 can infect oligodendrocytes	Less robust evidence than EBV
Smoking	Increases oxidative stress, promotes BBB disruption, enhances pro-inflammatory responses	Dose-dependent risk increase; also worsens disease progression
Obesity (adolescent)	Adipose tissue produces pro-inflammatory cytokines (leptin, IL-6, TNF-α); also associated with lower vitamin D levels	2× increased risk with adolescent obesity
Gut microbiome	Dysbiosis may shift balance toward pro-inflammatory immune responses	Emerging evidence; altered microbiome composition in MS patients

EBV and MS — Exam Favourite

The EBV–MS link is one of the strongest infectious disease–autoimmune associations known. The key study (Bjornevik et al., Science 2022) followed 10 million US military personnel: MS risk increased 32-fold after EBV seroconversion. However, EBV infection alone is necessary but NOT sufficient — >95% of adults are EBV-seropositive, yet only a tiny fraction develop MS. This implies additional hits (genetic susceptibility, other environmental factors) are required.

Lower prevalence than Western countries, but rising
Asian MS patients more often present with opticospinal phenotype
Must distinguish from NMOSD (anti-AQP4 antibody positive), which is relatively more common in Asian populations and requires different treatment
MOG-IgG+ disease (ADEM, ON, myelitis) is also an important differential in the Asian context ^[2]

5. Pathophysiology

Disrupted blood-brain barrier → autoreactive T cell + B cell infiltration → microglia and astrocyte activation → white + grey matter demyelination (cortical lesions, brain atrophy) ^[2]

Let's break this down step by step:

5.2 Step-by-Step Pathogenesis

In genetically susceptible individuals, autoreactive CD4+ T cells (particularly Th1 and Th17 subsets) escape thymic negative selection or peripheral tolerance mechanisms
These T cells recognise myelin-derived antigens: myelin basic protein (MBP), proteolipid protein (PLP), myelin oligodendrocyte glycoprotein (MOG)
Environmental triggers (e.g., EBV infection) may activate these autoreactive T cells through molecular mimicry (viral peptides resemble myelin antigens) or bystander activation

Activated T lymphocytes cross the BBB ^[4] using adhesion molecules (VLA-4 binding to VCAM-1 on endothelial cells — this is the target of natalizumab)
Matrix metalloproteinases (MMPs) help break down the BBB basement membrane
BBB disruption allows entry of immune cells, antibodies, and complement into the CNS

Autoreactive T cells recognise myelin-derived antigens presented by local APCs (microglia, perivascular macrophages) on MHC class II molecules ^[4]
Cytokine release → acute inflammation → acute clinical deficit (steroid-amenable) ^[4]
Pro-inflammatory cytokines: IFN-γ (Th1), IL-17 (Th17), TNF-α
B cells also play a critical role: antigen presentation, cytokine production, and antibody secretion (this is why anti-CD20 therapies like ocrelizumab are effective)
Complement activation and antibody-mediated cytotoxicity contribute to myelin and oligodendrocyte destruction

Macrophage destruction of the oligodendrocyte-myelin unit → demyelination plaques → decreased conduction → chronic deficit ^[4]
Active plaques: hypercellular with abundant macrophages, T cells, myelin debris (lipid-laden macrophages)
Chronic inactive plaques: hypocellular, gliotic scar tissue (astrocytic scarring = the "sclerosis"), axonal loss
Shadow plaques: areas of remyelination (thinner myelin sheaths) — evidence that repair can occur, but is often incomplete

Repeated attacks → axonal loss → progressive deficit ^[4]
Axonal transection occurs even in early disease — it is the pathological correlate of irreversible disability
Mechanisms of axonal damage:
- Direct inflammatory injury (cytokines, reactive oxygen species)
- Loss of trophic support from oligodendrocytes
- Energy failure: demyelinated axons require more energy to conduct (redistribute ion channels across the entire axon surface instead of just at nodes); if mitochondrial function is impaired, this leads to axonal degeneration
- Chronic microglial activation (smouldering inflammation)
Grey matter involvement: cortical demyelination and brain atrophy — correlates better with cognitive decline and progressive disability than white matter lesions

Why Steroids Help Acutely but Don't Change Long-Term Outcome

Acute relapses involve BBB disruption and active inflammation (cytokine storm, oedema, immune cell infiltration). Corticosteroids reduce BBB permeability, suppress acute inflammation, and speed recovery from a relapse — but they do NOT prevent the cumulative axonal damage that drives long-term disability. This is why disease-modifying therapies (DMTs) are needed to prevent relapses and slow progression.

Relapse: new inflammatory demyelinating lesion forms → conduction block → new neurological deficit
Remission: inflammation subsides → oedema resolves → partial remyelination → conduction partially restored → clinical improvement
Progressive phase: accumulated axonal loss exceeds the brain's compensatory capacity ("brain reserve") → gradual worsening without distinct relapses

6. Classification / Clinical Patterns

This is one of the most frequently tested aspects of MS.

Clinical patterns ^[2]^[3]^[4]:

Phenotype	Abbreviation	Frequency	Description
Clinically Isolated Syndrome	CIS	N/A	First attack of a disease compatible with MS that exhibits characteristics of inflammatory demyelination but has yet to fulfil MS diagnostic criteria. NO evidence of previous episodes ^[3]
Relapsing-Remitting	RRMS	85–90% ^[3]^[4]	Clearly defined relapses with full recovery or with residual deficit upon recovery. Minimal disease progression between relapses ^[3]
Secondary Progressive	SPMS	~50% at 15 years ^[4]; 75% of RRMS go into SPMS ^[2]	Initial RRMS course followed by gradual worsening ± occasional relapses. Transition occurs 10–20 years after onset ^[3]
Primary Progressive	PPMS	~10–15% ^[4]	Progressive accumulation of disability from onset with occasional plateaus, temporary minor improvement or acute relapses. Most common presentation is spinal cord syndrome with spastic paraparesis and no clear sensory level ^[3]
Progressive Relapsing	PRMS	~5% ^[4]	Relapses superimposing on a progressive course from the beginning ^[4]

CIS vs RRMS — When Does It Become MS?

CIS is a single demyelinating event (e.g., optic neuritis, partial myelitis, brainstem syndrome). It becomes MS when you can demonstrate dissemination in space AND time — either clinically (second attack in a different CNS region) or radiologically (new MRI lesions at follow-up, or simultaneous presence of enhancing and non-enhancing lesions). Under the 2017 McDonald Criteria, CSF oligoclonal bands can substitute for dissemination in time.

Active vs Inactive: based on clinical relapses and/or new MRI activity (gadolinium-enhancing or new/enlarging T2 lesions) within a defined time period
With progression vs Without progression: based on confirmed disability worsening over time
Modern classification (Lublin 2014) describes phenotypes as: Relapsing (CIS, RRMS) vs Progressive (PPMS, SPMS), each further qualified as active/not active and with/without progression

High Yield: In the 2017 revised McDonald Criteria, the distinction between PPMS and RRMS diagnostically now uses the same unifying framework — both require dissemination in space. PPMS requires 1 year of progressive disability PLUS 2 of 3 supportive criteria (brain DIS, spinal cord DIS, CSF OCBs).

7. Clinical Features

Attacks usually come on over days or weeks and resolve over weeks or months ^[4]
Heterogeneity in clinical features, severity, and response to disease-modifying therapies ^[1]
Clinical history: recurrent episodes of neurological symptoms or dysfunction with partial or complete (early) recovery ^[1]
The pattern of relapse-remission is the clinical hallmark — patients get better between attacks, especially early in the disease

7.2 Symptoms (Organised by System)

Four key areas: sensory + cerebellar + UMN (pyramidal) + optic ^[2]

Common presenting features ^[4]:

Non-specific: fatigue, headache, depression, aching limbs
Specific: sensory disturbance (40%), retrobulbar neuritis (17%), limb weakness (12%), diplopia (11%), vertigo, ataxia, sphincter disturbances (20%)

Optic neuritis (often the first presentation):

Decreased visual acuity (↓VA) ^[2]
Decreased colour vision ^[2] — particularly red desaturation (ask: "Does this red object look equally red with each eye?"). Why? The papillomacular bundle (carrying macular fibres responsible for central and colour vision) is preferentially affected.
Unilateral eye pain ^[2] — worse on eye movement ^[5]. Why? The optic nerve sheath is contiguous with the tendons of the extraocular muscles; inflammation of the nerve sheath is tugged during eye movement, causing pain.
Visual field defect: typically central scotoma ^[5] (macular fibres affected)
Symptoms worse in showers or exercise ^[5] — this is Uhthoff's phenomenon (see below)
Colour appears less vivid ^[5]

Ophthalmology Link — Optic Neuritis Exam Point

"Neurological exam: patient ≥50% have MS" ^[5] — i.e., ≥50% of patients presenting with optic neuritis will eventually develop MS. This makes optic neuritis a critical "gateway" presentation for MS diagnosis.

Spastic paraparesis, especially lower limbs ^[2] — Why LL more than UL? The corticospinal tract fibres serving the lower limbs are located more laterally and superficially in the spinal cord, making them more vulnerable to periventricular/perivenular plaques. Also, longer tracts = more area at risk.
Limb weakness — typically upper motor neuron pattern (pyramidal distribution: extensors weaker in upper limbs, flexors weaker in lower limbs)
Stiffness and spasms (spasticity)
PPMS most commonly presents as a spinal cord syndrome with spastic paraparesis and no clear sensory level ^[3]

Paraesthesia / hypaesthesia ^[2] — tingling, numbness, "pins and needles." When spinothalamic tract (STT) is affected: altered pain and temperature sensation. When dorsal columns (DCML) are affected: altered proprioception and vibration.
Lhermitte's sign ^[2]^[4]: cervical posterior column involvement — forced neck flexion gives rise to electric shock sensation down the body ^[4]. Why? Neck flexion stretches the posterior columns of the cervical cord, and in a demyelinated segment, this mechanical stretch triggers ectopic nerve impulse generation (ephaptic transmission), producing the "electric shock" feeling radiating down the spine and into the limbs.
Band-like tightness around the trunk ("MS hug") — demyelination of sensory fibres in the thoracic cord
Sensory useless hand (proprioceptive loss in hands)

Ataxia ^[2] — unsteady gait, difficulty with balance
Intention tremor — worsening tremor as the hand approaches a target (finger-nose test)
Scanning/staccato speech — cerebellar dysarthria
These can be devastating and are often prominent in the progressive phase

Diplopia ^[4] — double vision, often due to INO (see below)
Dysarthria, dysphagia (bulbar symptoms) ^[2]
Vertigo ^[4]
Facial weakness (UMN type) ^[2]
Trigeminal neuralgia — MS is an important cause of trigeminal neuralgia in young adults (typical trigeminal neuralgia occurs in elderly)

Bladder dysfunction (>90%) ^[2]: urgency (most common) ^[2], frequency, retention of urine, incontinence. Why? Demyelination of suprasacral spinal cord pathways disrupts the pontine micturition centre's control over the detrusor muscle, causing detrusor hyperreflexia (overactive bladder → urgency) or detrusor-sphincter dyssynergia (→ retention).
Bowel dysfunction (e.g., constipation) ^[2]
Sexual dysfunction ^[2] — erectile dysfunction in men, anorgasmia in women

Cognitive impairment: affects 40–70% of MS patients — information processing speed, memory, executive function
Depression: very common (~50% lifetime prevalence); partly reactive, partly neurobiological (white matter lesions disrupting mood circuits)
Fatigue: the most common symptom overall in MS — reported by up to 80% of patients. Multifactorial: central (CNS lesions, cytokines), peripheral (deconditioning), and psychological (depression, sleep disturbance).
Euphoria (in advanced disease, less common than previously believed)
Pseudobulbar affect (pathological laughing/crying)

Tonic spasms (painful brief tonic posturing of a limb)
Trigeminal neuralgia
Paroxysmal dysarthria
These are caused by ephaptic transmission — ectopic impulse generation in demyelinated axons, where one axon's impulse "jumps" to adjacent demyelinated axons

7.3 Signs (Organised by Examination)

RAPD (Relative Afferent Pupillary Defect) positive ^[2] — swinging flashlight test. Why? Demyelination of the optic nerve reduces afferent pupillary input on the affected side. When you swing the light from the normal eye to the affected eye, both pupils paradoxically dilate because the affected eye transmits less light information.
Optic atrophy on fundoscopy ^[2] — pale optic disc (temporal pallor characteristically). Why? Loss of retinal ganglion cell axons → pallor. In acute optic neuritis, the disc may look normal (retrobulbar neuritis: "the patient sees nothing and the doctor sees nothing") or mildly swollen.
Fundus may look normal in retrobulbar optic neuritis ^[5]
Decreased visual acuity, colour vision (Ishihara plates), visual field (central scotoma)

Bilateral internuclear ophthalmoplegia (INO) ^[2]^[4] — THE classic MS eye sign. Why bilateral? The MLF (medial longitudinal fasciculus) runs close to the midline in the brainstem; a single periventricular plaque can affect both sides.
- INO: On attempted lateral gaze, the adducting eye (medial rectus) fails to adduct (or is slow to adduct), while the abducting eye shows nystagmus. This is because the MLF connects CN VI nucleus (abducens) to the contralateral CN III (oculomotor) subnucleus for medial rectus — when the MLF is demyelinated, this connection fails.
- Bilateral INO in a young adult = MS until proven otherwise
Conjugate horizontal gaze palsy ^[2]
One-and-a-half syndrome ^[2] — combination of ipsilateral conjugate gaze palsy + ipsilateral INO = the eye on the affected side cannot move in any horizontal direction, the contralateral eye can only abduct. This happens when a lesion affects both the PPRF/CN VI nucleus AND the ipsilateral MLF.

Pyramidal signs ^[2] — because corticospinal tract lesions produce UMN pattern:
- Increased tone (spasticity — velocity-dependent, "clasp-knife")
- Hyperreflexia
- Clonus (sustained rhythmic contractions at ankle)
- Babinski sign positive (extensor plantar response)
- Weakness in pyramidal distribution

Loss of proprioception and vibration → sensory ataxia with Romberg's test positive ^[2] (dorsal column involvement)
Decreased pin-prick and temperature sensation (spinothalamic tract)
Myelopathic hand signs (e.g., pseudoathetosis) ^[2] — involuntary writhing movements of outstretched fingers when eyes are closed, due to impaired proprioception

Ataxia, dysmetria, dysdiadochokinesia ^[2]
Intention tremor (finger-nose test)
Heel-shin ataxia
Truncal ataxia (wide-based gait)
Nystagmus (cerebellar type: direction-changing, worse looking toward side of lesion)

These are the "buzzword" signs examiners love:

Sign/Phenomenon	Description	Pathophysiological Basis
Uhthoff's phenomenon ^[2]	Symptoms worsen in heat (hot bath, exercise, fever)	Heat-induced conduction blockade ^[2]: increased temperature further impairs conduction in marginally functioning demyelinated axons. Even a 0.5°C rise can block conduction in demyelinated fibres (the safety factor for impulse transmission is reduced). "Raised temperature → nerve transmission slows down, so worse in hot shower / exercise" ^[5]
Lhermitte's sign ^[2]^[4]	Electric shock sensation down spine/limbs on neck flexion	Cervical posterior column involvement ^[4]: mechanical stretching of demyelinated dorsal column fibres causes ectopic impulse generation
Bilateral INO ^[2]^[4]	Impaired adduction on lateral gaze + nystagmus of abducting eye, bilateral	Demyelination of MLF bilaterally — pathognomonic of MS in young adults
RAPD (Marcus Gunn pupil) ^[2]	Paradoxical pupil dilation when light swung to affected eye	Reduced afferent input from demyelinated optic nerve

Classical signs/symptoms of MS: Bilateral INO, Lhermitte's, Uhthoff's, Relapsing-Remitting course, Young (15–50y) onset, and PAINFUL EYES (optic neuritis) ^[4]

Uhthoff's Phenomenon vs Lhermitte's Sign — Don't Confuse!

Uhthoff's = heat makes symptoms WORSE (conduction block in demyelinated axons at higher temperatures)
Lhermitte's = neck flexion triggers electric shock down spine (mechanical stretch of demyelinated dorsal columns) Both are characteristic of MS but test different things. Uhthoff's is not specific to MS (can occur in any demyelinating condition). Lhermitte's is also seen in cervical spondylotic myelopathy, subacute combined degeneration (B12 deficiency), and radiation myelopathy.

Subtype	Typical Presentation
RRMS	Episodic neurological deficits (optic neuritis, sensory symptoms, limb weakness) with recovery; minimal disability between attacks early on
SPMS	Often pyramidal weakness + cerebellar signs ^[2]; gradual worsening gait, increasing spasticity, cognitive decline
PPMS	Spinal cord syndrome: progressive spastic paraparesis, gait difficulty, bladder dysfunction; no clear sensory level ^[3]; older onset (average ~40), more equal sex ratio

Understanding how MS fits within the broader category of CNS inflammatory demyelinating diseases (IDD) ^[2]:

Disease	Target	Antibody	Key Features
MS	Myelin (oligodendrocyte-myelin unit)	No specific diagnostic antibody	Dissemination in space + time; periventricular lesions; OCBs in CSF
NMOSD	Aquaporin-4 on astrocyte foot processes	Anti-AQP4 (NMO-IgG)	Severe bilateral optic neuritis; LETM (≥3 segments); area postrema syndrome (intractable nausea/vomiting) ^[6]
MOG-IgG+ disease	Myelin oligodendrocyte glycoprotein	Anti-MOG	ADEM, optic neuritis, myelitis; children > adults; better prognosis than NMOSD ^[2]

MS vs NMOSD — Critical Distinction

This is extremely important because MS and NMOSD require fundamentally DIFFERENT treatments. Some MS drugs (e.g., fingolimod, natalizumab, interferon-β) can WORSEN NMOSD. Always check anti-AQP4 and anti-MOG antibodies in suspected CNS demyelinating disease, especially in Asian patients where NMOSD is relatively more common.

9. Relevant Pathology

Plaques: well-demarcated areas of discolouration (grey-brown vs normal white matter) scattered throughout the CNS
Often periventricular, in optic nerves, brainstem, cerebellum, and spinal cord
Cortical lesions increasingly recognised on high-field MRI

Plaque Type	Features
Active plaque	Abundant lipid-laden macrophages (myelin breakdown), perivascular lymphocytic (T cell, B cell) infiltrates, activated microglia, relative axonal preservation (early)
Chronic active (smouldering) plaque	Inactive centre with rim of activated microglia/macrophages — drives slow expansion and progressive tissue damage
Chronic inactive plaque	Hypocellular, dense astrogliosis (scar = "sclerosis"), severe axonal loss, no ongoing inflammation
Shadow plaque	Remyelinated area with characteristically thin myelin sheaths — evidence of attempted repair

Clinical Feature	Pathophysiological Basis
Relapsing-remitting course	New inflammatory lesions (relapse) → inflammation resolves, partial remyelination (remission)
Progressive disability	Cumulative axonal loss exceeds compensatory capacity
Uhthoff's phenomenon	Heat impairs already marginal conduction in demyelinated axons
Lhermitte's sign	Mechanical stretch of demyelinated dorsal column fibres → ectopic impulses
Optic neuritis pain on eye movement	Inflammation of optic nerve sheath, which is attached to EOM tendons
Bilateral INO	Periventricular plaque affecting MLF bilaterally
Urgency (bladder)	Disruption of suprasacral pathways → detrusor hyperreflexia
Spastic paraparesis	Corticospinal tract demyelination → UMN signs
Sensory ataxia	Dorsal column demyelination → loss of proprioception
Fatigue	Multifactorial: central (cytokines, axonal damage), peripheral, psychological

High Yield Summary

Definition: Chronic inflammatory demyelinating neurodegenerative disease of the CNS; characterised by dissemination in space and time.

Epidemiology: F:M = 3:1; mean onset ~32 years; prevalence 5–300/100,000 depending on geography; ~1/1000 in HK. Important cause of non-traumatic disability in young adults.

Risk Factors: HLA-DRB1*15:01; EBV infection (32× risk); low vitamin D/sunlight; smoking; adolescent obesity.

Pathophysiology: Autoreactive T/B cells cross disrupted BBB → recognise myelin antigens → inflammatory demyelination → conduction block (acute deficit) → repeated attacks → axonal loss (progressive disability).

Clinical Subtypes: CIS → RRMS (85–90%) → SPMS (75% eventually); PPMS (~10–15%); PRMS (~5%).

Classic Features: Optic neuritis (pain on eye movement, ↓VA, ↓colour, RAPD); bilateral INO; Lhermitte's sign; Uhthoff's phenomenon; spastic paraparesis; cerebellar ataxia; bladder urgency.

Four Key Areas: Sensory + Cerebellar + UMN (pyramidal) + Optic.

Must Distinguish From: NMOSD (anti-AQP4), MOG-IgG+ disease — different treatment required.

Diagnosis requires: Clinical history of recurrent neurological episodes + supportive MRI and CSF findings + exclusion of mimics.

Active Recall — Multiple Sclerosis (Definition, Epidemiology, Pathophysiology, Clinical Features)

Differential Diagnosis of Multiple Sclerosis

The diagnostic challenge in MS is that it is a clinical chameleon — it can mimic, and be mimicked by, a vast number of neurological and systemic diseases. The fundamental reason is that MS produces multifocal CNS white matter lesions, and many other diseases do the same thing. The cornerstone GC lecture slide makes this explicit:

Diagnosis of Multiple Sclerosis: Clinical history (recurrent episodes of neurological symptoms or dysfunction with partial or complete recovery) PLUS supportive Ix findings (typically compatible MRI findings and presence of CSF oligoclonal bands) PLUS exclusion of other diseases that mimic MS ^[1]

That last point — exclusion of other diseases that mimic MS — means the differential diagnosis is not just academic; it is a mandatory diagnostic step. You cannot diagnose MS without actively ruling out mimics. MS is, in part, a diagnosis of exclusion layered on top of positive diagnostic criteria.

When you see a young patient with relapsing multifocal CNS symptoms, your mental differential should be organised by pathological category. The GC and medicine lecture slides provide this framework directly:

Pathological differentials for neurological deficits ^[7]^[8]:

Vascular (stroke)
Infection (encephalitis, myelitis, old polio)
Neoplasm (brain tumour, Pancoast tumour)
Degenerative (Parkinson's disease, cervical myelopathy/radiculopathy)
Inflammatory (multiple sclerosis, myelitis, Guillain-Barré syndrome, vasculitic neuropathy)
Congenital (cerebral palsy, syringomyelia)
Autoimmune (encephalitis, neuromyelitis optica, myasthenia gravis)
Trauma / Toxins (subdural/epidural haematoma; neuropathy secondary to chemotherapy)
Endocrine (B12 deficiency resulting in neuropathy/myelopathy, diabetic neuropathy)

The approach is to use the VINDICATE mnemonic (Vascular, Infectious, Neoplastic, Degenerative, Inflammatory/Autoimmune, Congenital, Trauma/Toxin, Endocrine) and systematically exclude each category.

Additionally, time course is critical for narrowing the differential ^[9]:

Sudden and improving: stroke, mononeuropathy
Gradually worsening over days or weeks: cerebral mass, demyelinating polyneuropathy
Evolving over months or years: meningioma, cervical spondylotic myelopathy
Wax and wane: multiple sclerosis

The "wax and wane" pattern is the key temporal signature of MS — if a patient's neurological symptoms don't fluctuate/relapse-remit, think harder about alternatives.

3. Key Differential Diagnoses — Organised and Explained

3.1 Other CNS Inflammatory Demyelinating Diseases (The Closest Mimics)

These are the diseases that share the most clinical overlap with MS and are the most important to distinguish because they require different treatments.

Neuromyelitis optica (NMO) is an inflammatory disorder of the CNS characterised by severe immune-mediated demyelination and axonal damage predominantly targeting optic nerves and spinal cord ^[3].

Feature	MS	NMOSD
Target	Myelin (oligodendrocyte)	AQP4 on astrocyte foot processes ^[6]
Antibody	None specific	Anti-aquaporin-4 (AQP4) antibody — specific for NMO and separates it from MS ^[3]
Optic neuritis	Usually unilateral, moderate severity, good recovery	Severe, often bilateral or rapidly sequential, poor recovery ^[3]^[6]
Myelitis	Short-segment (< 3 vertebral segments), partial cord	Longitudinally extensive transverse myelitis (LETM) ≥ 3 spinal segments ^[6]
Brainstem	INO (MLF lesion) common	Area postrema syndrome (intractable nausea and vomiting) — characteristic ^[6]
Brain MRI	Periventricular "Dawson's fingers," juxtacortical, infratentorial	Often normal or non-MS pattern lesions (periependymal, hypothalamic)
CSF OCBs	Present in >90%	Usually absent
Course	RRMS common; progressive forms	Usually relapsing; attacks tend to be more severe with worse recovery

Why Does This Matter So Much?

Some MS disease-modifying therapies (interferon-β, fingolimod, natalizumab) can worsen NMOSD by shifting the immune balance unfavourably. NMOSD requires B-cell targeted therapies (rituximab, eculizumab, satralizumab, inebilizumab). Getting this wrong can cause devastating harm. Always check anti-AQP4 antibodies, especially in Asian patients.

Myelin oligodendrocyte glycoprotein (MOG)-IgG+ disease ^[2] — "MOG" = myelin oligodendrocyte glycoprotein, a protein on the outermost surface of the myelin sheath, making it a convenient target for circulating antibodies.

Presentations: ADEM (acute disseminated encephalomyelitis), optic neuritis, myelitis ^[2]
More common in children than adults
Tends to have better recovery per attack than NMOSD
May be monophasic or relapsing
Optic neuritis often involves the anterior optic nerve with disc swelling (vs. retrobulbar in typical MS)
Myelitis: LETM like NMOSD, but often involves the conus (lower cord)
Anti-MOG antibodies are the diagnostic marker
MRI brain: large fluffy T2 lesions, often non-periventricular (unlike MS)

Autoimmune demyelinating disease of CNS that typically follows an immunisation or vaccination (post-vaccination encephalomyelitis) or systemic viral infection (parainfectious encephalomyelitis) ^[3].

Feature	MS	ADEM
Age	Young adults (15–50)	Children (typically < 10 years)
Course	Relapsing-remitting	Monophasic (single event)
Onset	Subacute (days–weeks)	Acute (days), often with encephalopathy (confusion, drowsiness) — MS does NOT usually cause encephalopathy
Preceding event	Usually none	Recent viral illness or vaccination (1–4 weeks prior)
MRI	Well-defined periventricular lesions	Large, poorly demarcated, bilateral white matter lesions; may also involve deep grey matter (thalamus, basal ganglia)
CSF	OCBs positive (>90%)	OCBs usually negative
Prognosis	Chronic relapsing	Usually good recovery; may evolve to MS if further attacks occur

Why distinguish? ADEM is typically monophasic and treated with acute steroids; if it recurs, reconsider the diagnosis (could be MOG-IgG+ disease or MS).

3.2 Systemic Autoimmune / Inflammatory Diseases with CNS Involvement

SLE can present as a recurrent neurologic syndrome before systemic manifestation occurs ^[3].

This is an important mimic because:

Neuropsychiatric SLE (NPSLE) can produce multifocal CNS white matter lesions on MRI that look like MS plaques
Can cause optic neuritis, transverse myelitis, cognitive dysfunction, seizures
How to differentiate: Look for systemic features (malar rash, arthritis, serositis, cytopenias, renal disease); check ANA, anti-dsDNA, complement levels (C3/C4); SLE patients often have antiphospholipid antibodies
SLE-associated myelitis tends to involve the grey matter (central cord) and may be LETM-pattern

Sarcoidosis is a systemic granulomatous disease that can involve the CNS (neurosarcoidosis occurs in ~5–10% of sarcoidosis patients)
Can cause cranial neuropathies (especially CN VII — facial nerve palsy), optic neuritis, myelitis, meningitis, hypothalamic/pituitary dysfunction
MRI: may show leptomeningeal enhancement (unlike MS which has parenchymal lesions), but can also produce white matter lesions
How to differentiate: Serum ACE (angiotensin-converting enzyme) may be elevated; CXR/CT chest for bilateral hilar lymphadenopathy; tissue biopsy showing non-caseating granulomas is definitive; CSF may show lymphocytic pleocytosis with low glucose (unlike MS)

Inflammation of CNS blood vessels → multifocal ischaemic lesions that can mimic MS on MRI
Typically presents with headache, cognitive decline, strokes/TIAs, and seizures (seizures are uncommon in MS — a useful differentiator)
How to differentiate: Conventional angiography may show "beading" pattern; brain biopsy is the gold standard; CSF often shows elevated protein and pleocytosis; no OCBs
Secondary CNS vasculitis: consider Behçet's disease (oral/genital ulcers, pathergy test), polyarteritis nodosa, granulomatosis with polyangiitis

Can cause CNS involvement mimicking MS, including optic neuritis, myelitis, and white matter lesions on MRI
How to differentiate: Dry eyes (keratoconjunctivitis sicca), dry mouth (xerostomia); anti-Ro (SS-A) and anti-La (SS-B) antibodies; Schirmer's test; salivary gland biopsy

Neuro-Behçet's can produce brainstem and white matter lesions mimicking MS
How to differentiate: Recurrent oral ulcers, genital ulcers, uveitis, pathergy test positive; more common in populations along the ancient Silk Road (Turkey, Middle East, East Asia including HK/China)

3.3 Infectious Causes

Caused by JC virus reactivation in immunosuppressed patients (HIV/AIDS, on natalizumab for MS — ironic and important)
Progressive multifocal white matter disease (not relapsing-remitting)
MRI: large confluent white matter lesions, typically non-enhancing, no mass effect
How to differentiate: Check HIV status; JC virus PCR in CSF; clinical context (immunosuppression)

HIV can cause a vacuolar myelopathy and diffuse white matter disease
Can also predispose to CNS infections (toxoplasmosis, CMV, cryptococcus) and PML

Chronic infective myelopathy: HTLV-1 infection ^[10]
Slowly progressive spastic paraparesis — can mimic PPMS
Endemic in Japan, Caribbean, Sub-Saharan Africa
How to differentiate: HTLV-1 serology; CSF HTLV-1 antibodies

"The great imitator" — can produce almost any neurological syndrome
Can cause meningovascular disease (strokes), tabes dorsalis (dorsal column dysfunction), general paresis
How to differentiate: RPR/VDRL, FTA-ABS; CSF VDRL is specific but not sensitive
Increasingly relevant in Hong Kong with rising syphilis rates

Tick-borne spirochete (Borrelia burgdorferi)
Can cause facial nerve palsy, radiculopathy, meningitis, and CNS white matter lesions
Not common in Hong Kong (endemic in North America, Europe) but important for exam completeness
How to differentiate: Tick exposure history, erythema migrans rash, Lyme serology

3.4 Vascular Causes

MS appears in the DDx of stroke ^[11]: Differential diagnosis of stroke includes: intracranial tumour, chronic subdural haematoma, encephalitis, multiple sclerosis, seizure, hysteria ^[11].

Conversely, stroke is in the DDx of MS:

Small vessel disease in young patients (e.g., CADASIL — cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) produces multifocal white matter lesions on MRI
CADASIL: autosomal dominant, NOTCH3 mutations; migraine with aura, recurrent strokes, cognitive decline, psychiatric symptoms; temporal pole white matter lesions are characteristic
Antiphospholipid syndrome (APS): young strokes/TIAs, livedo reticularis, pregnancy morbidity; check anticardiolipin, anti-β2-glycoprotein I, lupus anticoagulant
How to differentiate from MS: Stroke produces acute onset (minutes–hours) deficits that correspond to vascular territories (not disseminated white matter). MS deficits develop over days–weeks and don't respect vascular territories.

Spinal dural AV fistula ^[12]
Progressive myelopathy (can mimic PPMS)
Middle-aged/elderly males
How to differentiate: MRI spine shows flow voids and cord signal change; spinal angiography is diagnostic

3.5 Neoplastic Causes

Primary CNS lymphoma can produce multifocal enhancing white matter lesions
Can be steroid-responsive (initially shrinks with steroids, like MS lesions — a diagnostic trap!)
How to differentiate: Lesions tend to be periventricular and homogeneously enhancing (vs. ring-enhancing or open-ring in MS); tissue biopsy; avoid empirical steroids before biopsy if lymphoma is suspected (steroids can cause "vanishing lesion" making biopsy non-diagnostic)

Low-grade gliomas can produce T2 hyperintense lesions mimicking MS plaques
Metastases: typically ring-enhancing, with surrounding oedema
How to differentiate: Mass effect, progressive (not relapsing-remitting), usually single enhancing lesion (or few lesions with significant oedema)

Antibody-mediated CNS syndromes (e.g., anti-NMDA receptor encephalitis, anti-amphiphysin myelopathy)
Can produce multifocal CNS disease
How to differentiate: Search for underlying malignancy (CT body, tumour markers); specific neural antibody panels

3.6 Degenerative / Structural Causes

Degenerative: spondylosis, disc prolapse ^[10]
Compressive myelopathy ^[12]
Progressive spastic paraparesis with sensory disturbance — can mimic PPMS
Very common in middle-aged/elderly patients
How to differentiate: MRI cervical spine shows disc/osteophyte compression of the cord with myelopathic signal change at ONE level (vs. MS which has lesions at multiple levels and often has brain lesions too). No OCBs in CSF. No brain lesions on MRI.
Lhermitte's sign can also occur in cervical spondylotic myelopathy — so Lhermitte's is NOT pathognomonic for MS

Congenital: syringomyelia (cyst within spinal cord) ^[10]
Fluid-filled cavity in the central spinal cord
Produces a "cape-like" dissociated sensory loss (loss of pain/temperature with preserved light touch/proprioception) due to crossing spinothalamic fibres being disrupted
How to differentiate: MRI shows the syrinx; typically associated with Chiari malformation; no brain white matter lesions

3.7 Metabolic / Nutritional Causes

Vitamin B12 deficiency resulting in neuropathy/myelopathy ^[7]^[8]
Demyelination of dorsal columns AND corticospinal tracts → combined UMN + sensory ataxia (similar to MS spinal cord involvement)
Lhermitte's sign can be positive
How to differentiate: Check serum B12, methylmalonic acid, homocysteine; peripheral blood film may show megaloblastic anaemia; no brain periventricular lesions; no OCBs

Produces a syndrome almost identical to B12 deficiency
Often seen after gastric bypass surgery or excess zinc intake
Check serum copper and caeruloplasmin

Hysteria is listed as a DDx of stroke ^[11] and can also mimic MS
Patients present with neurological symptoms (weakness, sensory loss, visual disturbance) without organic disease
Important consideration in young women (same demographic as MS)
How to differentiate: Positive signs of functional disorder (Hoover's sign, give-way weakness, tubular visual field loss); normal MRI; normal CSF; symptoms often don't follow neuroanatomical patterns
Caution: MS and FND can coexist — do not dismiss new symptoms in a known MS patient as "functional" without appropriate investigation

Alemtuzumab (anti-CD52) is listed as a treatment of relapsing-remitting multiple sclerosis, but 3rd line in HA ^[13]. While not a DDx per se, it is important to note that MS treatments themselves can cause complications that mimic new disease:

Natalizumab → risk of PML (JC virus reactivation)
Rituximab (anti-CD20) and alemtuzumab (anti-CD52) can reactivate occult Hepatitis B ^[13]
These treatment-related complications can produce new neurological symptoms in an MS patient, mimicking a relapse

Feature	MS	NMOSD	ADEM	SLE	CNS Lymphoma	Cervical Myelopathy
Age	15–50	Any (peak 30–40)	Children	15–45	> 50 (if immunocompetent)	> 50
Course	Relapsing-remitting → progressive	Relapsing (severe attacks)	Monophasic	Relapsing (with systemic flares)	Progressive	Progressive
Optic neuritis	Unilateral, moderate	Bilateral, severe	Rare	Possible	Rare	No
Myelitis	Short-segment, partial	LETM ≥ 3 segments	LETM	LETM possible	Rare	Compression at one level
Brain MRI	Periventricular, Dawson's fingers, callosal	Normal or non-MS pattern	Large, fluffy, bilateral	White matter lesions (non-specific)	Periventricular enhancing mass	Normal or incidental findings
CSF OCBs	Positive (>90%)	Usually negative	Usually negative	May be positive	May be positive	Negative
Specific antibody	None	Anti-AQP4	Anti-MOG (some)	ANA, anti-dsDNA	None	None
Systemic features	None	None	Post-viral, encephalopathy	Rash, arthritis, renal, serositis	B symptoms possible	Neck pain, radiculopathy

These are features that should prompt you to look harder for an alternative diagnosis:

Red Flag	Why It's Atypical for MS	Consider Instead
Persistent headache	MS rarely causes headache as a primary feature	CNS vasculitis, venous sinus thrombosis, intracranial mass
Seizures	Very rare in MS (<5%)	SLE, CNS vasculitis, encephalitis, tumour
Encephalopathy / reduced consciousness	MS preserves consciousness	ADEM, encephalitis, SLE
Peripheral neuropathy (LMN signs in limbs)	MS is purely CNS by definition	GBS, CIDP, vasculitic neuropathy, B12 deficiency
Bilateral severe optic neuritis with poor recovery	Typical MS ON is unilateral with good recovery	NMOSD
LETM ≥ 3 segments	MS myelitis is usually short-segment	NMOSD, MOG-IgG+ disease, SLE
Normal brain MRI with spinal cord disease	>95% of MS patients have brain lesions	NMOSD, dural AV fistula, spondylotic myelopathy
Age > 50 at onset	Possible but should raise suspicion	Cervical myelopathy, CNS lymphoma, small vessel disease
Prominent cortical signs (aphasia, neglect)	MS usually spares cortex clinically (early)	Stroke, tumour, encephalitis
Systemic symptoms (fever, rash, weight loss, joint pain)	MS has no systemic manifestations	SLE, sarcoidosis, vasculitis, lymphoma, infection

The Number One DDx Mistake

The most common high-stakes diagnostic error in MS is misdiagnosing NMOSD as MS. In Asian populations (including Hong Kong), NMOSD is relatively more common. Treating NMOSD with MS drugs (especially interferon-β or fingolimod) can be catastrophic. Always check anti-AQP4 and anti-MOG antibodies in any suspected CNS demyelinating disease, especially if there are red flags (bilateral optic neuritis, LETM, area postrema syndrome, negative brain MRI).

6. Differential Diagnosis in Specific Clinical Presentations

Because MS can present in many ways, the DDx depends on the presenting syndrome:

MS (most common cause in young adults)
NMOSD (more severe, bilateral)
MOG-IgG+ disease (often with disc swelling)
Infectious: syphilis, HIV ^[14]
Inflammatory: SLE, RA, post-viral infection (especially children) ^[14]
Ischaemic optic neuropathy (older adults — consider AAION/giant cell arteritis if ≥50) ^[14]
Compressive optic neuropathy (meningioma, pituitary tumour)

Differential diagnosis of myelopathy ^[10]:

Vascular: epidural haematoma, cord infarction, dural arteriovenous fistula
Infective: epidural abscess (Staph aureus, streptococci, anaerobes), TB spinal osteomyelitis, acute viral myelitis (HSV, VZV, HIV), chronic infective myelopathy (HTLV-1 infection, syphilis), post-infective (EBV, VZV, Mycoplasma) / post-immunisation
Neoplastic: extradural tumours, intramedullary tumours
Degenerative: spondylosis, disc prolapse
Inflammatory: rheumatoid arthritis, ankylosing spondylitis
Congenital: syringomyelia (cyst within spinal cord)
Autoimmune: neuromyelitis optica, multiple sclerosis
Trauma / toxin: vertebral fracture
Endocrine: Vitamin B12 deficiency

DDx of stroke ^[11]:

Intracranial tumour
Chronic subdural haematoma
Encephalitis
Multiple sclerosis
Seizure (Todd's paralysis)
Hysteria

MS can cause bulbar symptoms. The DDx of oropharyngeal dysphagia with neuromuscular causes includes ^[15]:

Central causes: stroke, brainstem tumours, Parkinson's disease
Peripheral causes: amyotrophic lateral sclerosis, myasthenia gravis, multiple sclerosis
Myopathy: myotonic dystrophy, dermatomyositis, polymyositis

Category	Condition	Key Distinguishing Feature
CNS demyelinating	NMOSD	Anti-AQP4 Ab; LETM; severe bilateral ON; area postrema syndrome
	MOG-IgG+ disease	Anti-MOG Ab; ADEM phenotype; children; anterior ON with disc swelling
	ADEM	Monophasic; post-viral/vaccination; encephalopathy; children
Systemic autoimmune	SLE	Systemic features; ANA/anti-dsDNA; NPSLE
	Sarcoidosis	Bilateral hilar LAD; elevated ACE; cranial neuropathies; non-caseating granulomas
	Sjögren's	Sicca symptoms; anti-Ro/La
	Behçet's	Oral/genital ulcers; uveitis; pathergy
Vascular	CADASIL	AD; NOTCH3; migraine with aura; temporal pole lesions
	APS	Young strokes; aPL antibodies; livedo reticularis
	Spinal dural AVF	Progressive myelopathy; middle-aged males; flow voids on MRI
Infectious	PML	JC virus; immunosuppressed; non-enhancing white matter lesions
	Neurosyphilis	RPR/VDRL/FTA-ABS; great imitator
	HTLV-1 myelopathy	Progressive spastic paraparesis; HTLV-1 serology
	Lyme disease	Tick exposure; facial palsy; erythema migrans
Neoplastic	CNS lymphoma	Homogeneous enhancing mass; steroid-responsive (trap!)
	Glioma	Progressive mass lesion; not relapsing
Degenerative	Cervical myelopathy	Single-level compression; no brain lesions; progressive
Metabolic	B12 deficiency	Megaloblastic anaemia; dorsal column + corticospinal signs; low B12
Functional	FND	Positive functional signs; normal MRI/CSF; can coexist with MS

High Yield Summary — Differential Diagnosis of MS

MS is partly a diagnosis of exclusion — must actively exclude mimics before diagnosing.
The most critical DDx is NMOSD (anti-AQP4): different treatment required; MS drugs can worsen NMOSD. Always check anti-AQP4 and anti-MOG antibodies.
Systemic autoimmune diseases (SLE, sarcoidosis, Sjögren's, Behçet's) can mimic MS — look for systemic features and check autoantibodies.
Red flags against MS: seizures, encephalopathy, peripheral neuropathy, LETM ≥ 3 segments, bilateral severe optic neuritis, normal brain MRI, systemic symptoms, age > 50.
Time course is key: MS waxes and wanes; stroke is sudden; tumours/degenerative conditions are progressive; ADEM is monophasic.
Infections to exclude: neurosyphilis, HIV, PML (especially if on natalizumab), HTLV-1, Lyme.
Structural mimics: cervical spondylotic myelopathy (very common), spinal dural AVF, syringomyelia.
FND can mimic and coexist with MS — never dismiss new symptoms without investigation.

Active Recall — Differential Diagnosis of MS

References

^[1] Lecture slides: GC 225. Neuroimmunological disorders of the central nervous system.pdf (p2, p8) ^[2] Senior notes: Maksim Medicine Notes.pdf (p261, section 11.8 CNS demyelinating diseases) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1272–1274, MS section III — Differential diagnosis) ^[6] Senior notes: learning_points_output.txt (Neurology — Two Cases of Lower Limb Weakness, Learning Point 2 on NMOSD) ^[7] Lecture slides: CFB_Neuro clinical skills demonstration_01.08.22_file to students.pdf (p8) ^[8] Lecture slides: Neurology- Two cases of lower limb weakness.pdf (p17–18) ^[9] Senior notes: Ryan Ho Fundamentals.pdf (p319) ^[10] Lecture slides: Neurology- Two cases of lower limb weakness.pdf (p29, Differential Diagnosis of Myelopathy) ^[11] Lecture slides: GC 087. Sudden hemiplegia dysphagia.pdf (p13, DDx of stroke) ^[12] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p1148, DDx of stroke including MS) ^[13] Senior notes: Block A - I am a hepatitis B carrier.pdf (p68, anti-CD20/anti-CD52 and MS treatment) ^[14] Senior notes: Ryan Ho Opthalmology.pdf (p92, section 4.3.3 Optic Neuritis causes and DDx) ^[15] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p326, DDx of dysphagia — neuromuscular causes)

Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Multiple Sclerosis

The diagnosis of MS rests on three pillars, as stated directly on the GC lecture slide:

Diagnosis of Multiple Sclerosis ^[1]:

Clinical history: recurrent episodes of neurological symptoms or dysfunction with partial or complete (early) recovery

Supportive Ix findings: typically compatible MRI findings and presence of CSF oligoclonal bands

Exclusion of other diseases that mimic MS

This framework is logical from first principles: MS is defined by dissemination in space and time within the CNS. The diagnostic criteria operationalise this definition using clinical and paraclinical evidence, while simultaneously ensuring you haven't been fooled by a mimic.

There is no single diagnostic test for MS — no blood test, no biopsy. The diagnosis integrates clinical assessment, imaging, and CSF analysis within a formal criteria framework.

2. The 2017 Revised McDonald Criteria

The McDonald Criteria (first published 2001, revised 2005, 2010, and most recently 2017) are the gold-standard diagnostic criteria for MS.

Diagnosis: revised McDonald criteria (2017) — Three components: DIT + DIS + exclude alternate DDx ^[2]

"Dissemination in space" means the disease process affects multiple distinct anatomical locations within the CNS. This is what separates MS from a localised process (e.g., a single tumour or a single stroke).

Dissemination in space (DIS) can be demonstrated by ^[2]^[3]:

T2-hyperintense lesions in ≥ 2 of the 4 MS-typical regions of CNS ^[2]^[3]:
1. Periventricular — lesions around the lateral ventricles (classic "Dawson's fingers")
2. Cortical / juxtacortical — lesions at the grey-white junction or within cortex (cortical lesions are a new addition in the 2017 criteria ^[2])
3. Infratentorial — brainstem and cerebellum
4. Spinal cord — cervical and thoracic most common
OR: Development of a further clinical attack implicating a different CNS site ^[3]

Why These 4 Regions?

These four regions were chosen because they are the characteristic predilection sites for MS plaques (perivenular white matter), AND they are locations that help distinguish MS from other conditions. For example, periventricular lesions are relatively specific to MS (vs. small vessel disease which tends to produce deeper white matter lesions). The 2017 addition of cortical lesions reflects improved MRI techniques that can now detect cortical demyelination.

"Dissemination in time" means the disease process is ongoing — new lesions are forming at different time points. This separates MS from a monophasic event like ADEM.

Dissemination in time (DIT) can be demonstrated by any one of ^[2]^[3]:

≥ 2 clinical attacks — the simplest: if a patient has had two clearly separate clinical episodes affecting different parts of the CNS, that's DIT
New T2-hyperintense or gadolinium-enhancing lesions on follow-up MRI (irrespective of timing of baseline MRI) ^[2] — you don't need to wait a specific interval; any new lesion on a repeat MRI counts
Simultaneous presence of gadolinium-enhancing and non-enhancing lesions at any time ^[2]^[3] — this is elegant: an enhancing lesion = an acute/active lesion (BBB is broken down, gadolinium leaks in); a non-enhancing lesion = an older lesion. If BOTH are present on a SINGLE MRI, it proves lesions formed at different times.
CSF oligoclonal bands (↑ intrathecal IgG production) ^[2] — this is a new addition in the 2017 criteria ^[2]. Previously, OCBs could only support but not substitute for DIT. Now, if CSF shows OCBs, this can substitute for MRI evidence of DIT. Why? Because OCBs indicate chronic intrathecal immune activation, implying an ongoing process rather than a single event.

The 2017 OCB Change — Very High Yield

The 2017 McDonald Criteria added two key modifications: (1) CSF oligoclonal bands can substitute for DIT, and (2) cortical lesions now count for DIS alongside juxtacortical lesions. These changes allow earlier diagnosis — a patient with CIS who has DIS on MRI and positive OCBs can now be diagnosed with MS without waiting for a second attack or a follow-up MRI.

Clinical Presentation	Additional Data Needed for MS Diagnosis
≥ 2 attacks + objective clinical evidence of ≥ 2 lesions	None — clinical evidence alone fulfils DIS + DIT
≥ 2 attacks + objective evidence of 1 lesion	DIS needed: MRI showing ≥ 2 of 4 MS-typical regions, OR await further clinical attack at different site
1 attack + objective evidence of ≥ 2 lesions (CIS with DIS)	DIT needed: Follow-up MRI with new lesions, OR simultaneous Gd+/Gd− lesions, OR CSF OCBs
1 attack + objective evidence of 1 lesion (CIS)	Both DIS AND DIT needed

PPMS cannot be diagnosed by the standard relapsing criteria because, by definition, there are no distinct relapses. The 2017 McDonald Criteria for PPMS require:

≥ 1 year of disability progression (retrospectively or prospectively determined)

PLUS ≥ 2 of the following 3:

DIS in the brain: ≥ 1 T2-hyperintense lesion in at least 1 MS-typical brain region (periventricular, cortical/juxtacortical, or infratentorial)
DIS in the spinal cord: ≥ 2 T2-hyperintense spinal cord lesions
CSF-specific OCBs: positive (by isoelectric focusing)

4. Investigation Modalities

The investigations for MS serve three purposes:

Support the diagnosis (demonstrate DIS + DIT)
Exclude mimics (the third pillar of diagnosis)
Monitor disease activity and progression

4.1 Imaging — MRI Brain and Whole Spine with Gadolinium Contrast

MRI brain + whole spine with gadolinium contrast ^[2] is the single most important investigation.

MRI brain and spinal cord (with and without contrast) — imaging modality of choice and is more sensitive than CT in detecting MS plaques ^[3]

Imaging: Brain – CT / MRI +/- vascular imaging; Spine – XR, MRI ^[16]

MRI exploits the magnetic properties of hydrogen atoms (abundant in water and fat) to create detailed images of soft tissue. The key advantage over CT in MS:

Superior soft tissue contrast — can distinguish demyelinated white matter from normal white matter
Can detect lesions in the posterior fossa (brainstem, cerebellum) and spinal cord where CT is limited by bone artefact
Gadolinium contrast (a paramagnetic agent) leaks through areas of BBB disruption, highlighting acute/active inflammation

Sequence	What It Shows	MS Findings
T2-weighted	Water appears bright (hyperintense)	Plaques appear as T2-hyperintense lesions ^[2]^[3] — both old and new plaques are bright because demyelinated tissue has increased water content (oedema acutely, gliosis chronically)
FLAIR (Fluid-Attenuated Inversion Recovery)	Like T2 but CSF signal is suppressed	Superior for detecting periventricular lesions (CSF signal "washed out" so lesions next to ventricles stand out clearly). T2/FLAIR-hyperintense ^[2]
T1-weighted (pre-contrast)	Fat appears bright; water appears dark	Old plaques: T1-iso or hypointense ("T1 black holes") ^[2] — these represent areas of severe tissue destruction (axonal loss, matrix destruction). T1 black holes correlate with permanent disability.
T1-weighted (post-gadolinium)	Areas of BBB breakdown enhance (appear bright)	New plaques: gadolinium-enhancing ^[2] — indicates active disease with BBB breakdown and leakage of Gd ^[2]. Enhancement typically lasts 2–8 weeks.

Findings suggestive of MS ^[3]:

Cerebral or spinal plaques are the characteristic lesion in MS
Typically occurs in periventricular region, corpus callosum, centrum semiovale ^[3]
Dawson's fingers: periventricular T2/FLAIR lesions oriented perpendicular to the lateral ventricles, following the course of the medullary veins. This is because MS plaques are perivenular — they form around small veins.
Callosal-septal interface lesions: lesions at the undersurface of the corpus callosum — relatively specific for MS (helps distinguish from small vessel disease, where lesions spare the corpus callosum)
Ovoid lesions: characteristic shape, with the long axis perpendicular to the ventricles

Active MS lesions vs Chronic MS lesions ^[3]:

Feature	Active Lesion	Chronic Lesion
Size	Tend to be larger, ill-defined margins ^[3]	Smaller, well-defined
T1-weighted	Hypointense ^[3]	May be isointense or hypointense ("T1 black hole")
T1 post-Gd	Gadolinium-enhancing ^[3] (ring or nodular enhancement; open-ring enhancement is relatively specific for demyelination vs. tumour/abscess which show closed ring)	Non-enhancing
T2/FLAIR	Hyperintense ^[3]	Hyperintense at centre only ^[3]

Open-Ring Enhancement — A Useful Sign

When an MS plaque shows ring enhancement, the ring is characteristically "open" — the enhancing arc faces the cortical grey matter, and the non-enhancing side faces the white matter. This pattern occurs because inflammation at the leading edge (towards grey matter) is active, while the white-matter side is already demyelinated. In contrast, abscesses and tumours typically show a closed (complete) ring of enhancement. This can help avoid unnecessary brain biopsy.

Neurodegeneration: brain atrophy of both grey matter and white matter with volume loss > 0.4%/year ^[2]

Brain volume loss (BVL) is measured on serial MRIs and is used as a marker of neurodegeneration. Normal age-related BVL is ~0.1–0.3%/year; MS patients typically lose >0.4%/year. This is one of the four parameters of the NEDA (No Evidence of Disease Activity) treatment goal.

4.2 CSF Analysis (Lumbar Puncture)

CSF (not routine) ^[2] — CSF analysis is not required for diagnosis in every patient (e.g., if clinical + MRI criteria clearly met), but it is very valuable and sometimes essential, especially in:

CIS (to establish DIT via OCBs without waiting for follow-up MRI)
Atypical presentations
Excluding mimics

Lumbar puncture ^[8]:

Total cell count
Protein / glucose
Microbiological workup (bacteria, viruses, TB...)
Cytology
Oligoclonal bands

CSF Parameter	Typical MS Finding	Interpretation
Oligoclonal IgG bands (OCBs)	Present in > 90% of MS patients ^[3]	Elevation of CSF immunoglobulin relative to other protein components suggests intrathecal synthesis ^[3]. OCBs are detected by isoelectric focusing — you run the CSF and serum side by side. If there are bands in the CSF that are NOT present in the serum, this proves the IgG is being made within the CNS (intrathecal synthesis), not just leaking in from the blood. Immunoglobulin increase is predominantly IgG ^[3].
Cell count	Mild lymphocytic pleocytosis (5–50 cells/μL)	Can occur, but if >50 cells, think harder about infection, sarcoidosis, or lymphoma
Protein	Normal or mildly elevated	↑CSF protein with lymphocytosis ^[4] can be seen. If markedly elevated, consider NMOSD, infection, GBS
Glucose	Normal	Low glucose should prompt consideration of TB, fungal, bacterial, or carcinomatous meningitis
Other CSF parameters are usually normal ^[3]

OCBs — The Key Points for Exams

OCBs are present in >90% of MS but only ~30% of NMOSD ^[17] — this is a key differentiator
OCBs are not specific to MS — they can be found in neurosyphilis, neurosarcoidosis, subacute sclerosing panencephalitis (SSPE), CNS lymphoma, and other chronic CNS inflammatory conditions
The 2017 McDonald Criteria allow OCBs to substitute for DIT — this was a major change that enables earlier diagnosis
You must compare CSF bands with serum bands: ≥ 2 bands in CSF not present in serum = positive

CSF in NMOSD: inflammatory profiles (oligoclonal bands in ~30%, vs. >85% in patients with multiple sclerosis) ^[17]

This is a very useful differentiating point: if CSF shows absent OCBs, NMOSD becomes relatively more likely than MS.

4.3 Blood Tests

Blood tests in MS primarily serve to exclude mimics rather than confirm the diagnosis. There is no diagnostic blood test for MS.

Basic blood tests ^[16]:

Complete blood count — for anaemia (B12 deficiency), cytopenias (SLE)
Inflammatory markers (ESR, CRP) — elevated in vasculitis, SLE, sarcoidosis, infection; typically normal in MS
Basic biochemistry — electrolytes, renal function, liver function
Vitamin B12 — to exclude subacute combined degeneration
Thyroid function tests — thyroid disease can cause fatigue, cognitive symptoms; also autoimmune comorbidity
Lipid profile, glucose — vascular risk factors (if considering small vessel disease as DDx)
Creatine kinase — elevated in myopathy (not MS)

Further blood tests ^[8]:

Autoimmune markers: ANA, anti-dsDNA, anti-ENA, C3, C4, ANCA — to exclude SLE, Sjögren's, vasculitis
Anti-AQP4 Ab — to exclude NMOSD (cell-based assay is the gold standard, more sensitive and specific than ELISA)
Anti-MOG Ab — to exclude MOG-IgG+ disease
Tumour markers and paraneoplastic antibodies — if paraneoplastic syndrome is suspected
Anti-AChR Ab — to exclude myasthenia gravis (if bulbar or ocular symptoms)

Antibodies: anti-AQP4, anti-MOG ^[2]

Always Check Anti-AQP4 and Anti-MOG

This cannot be overemphasised. In the Hong Kong / Asian context, where NMOSD and MOG-IgG+ disease are relatively more prevalent, these antibody tests are essential in ALL suspected CNS demyelinating disease. The cell-based assay for anti-AQP4 is the gold standard — ELISA has lower sensitivity. A negative ELISA does not exclude NMOSD; if clinical suspicion is high, send for cell-based assay.

Mimic	Blood Test
Neurosyphilis	RPR/VDRL, FTA-ABS (confirmatory)
HIV	HIV Ag/Ab combo test
Sarcoidosis	Serum ACE, calcium
Behçet's disease	No specific blood test; clinical diagnosis
CADASIL	Genetic testing (NOTCH3)
Lyme disease	Lyme serology (ELISA → Western blot)
Antiphospholipid syndrome	Anticardiolipin, anti-β2-glycoprotein I, lupus anticoagulant

4.4 Evoked Potentials

Visual evoked potential (VER) or brainstem auditory evoked potential (BAEP) ^[3]:

Evoked potentials are electrical events generated in the CNS by peripheral stimulation of a sensory organ
Evoked potentials are delayed in MS patients ^[3]

How it works: The patient watches a chequerboard pattern that alternates on a screen. Electrodes over the occipital cortex record the electrical response (the P100 wave, normally arriving at ~100 ms).
In MS: demyelination of the optic nerve slows conduction → prolonged P100 latency (e.g., 130 ms instead of 100 ms), even if the amplitude is preserved
Why useful: Can detect subclinical optic nerve demyelination — a patient with no visual symptoms who has prolonged VEP latency has evidence of a lesion they didn't know about, helping establish DIS
Limitation: VEPs are less used now because MRI is more sensitive. However, VEPs remain useful when MRI is equivocal or to demonstrate an optic nerve lesion that MRI may miss.

Somatosensory evoked potentials (SSEPs): electrical stimulation of peripheral nerves (median, tibial) → record over somatosensory cortex. Delayed in dorsal column lesions.
Brainstem auditory evoked potentials (BAEPs): auditory clicks → record brainstem responses. Can detect brainstem lesions.
These are supplementary; VEP is the most commonly used in MS practice.

Non-invasive imaging of the retina that measures retinal nerve fibre layer (RNFL) thickness
Thinning of the RNFL indicates optic nerve axonal loss (sequelae of optic neuritis)
Increasingly used as a biomarker for neurodegeneration in MS (thinner RNFL correlates with greater brain atrophy and disability)
Useful in monitoring and research; not part of the formal diagnostic criteria

Neurophysiological tests: nerve conduction studies, electromyography ^[16]
These are normal in MS (because MS is a CNS disease; NCS/EMG test the PNS)
Their role is to exclude PNS mimics (GBS, CIDP, motor neuron disease, myopathy)
If NCS/EMG is abnormal → reconsider the diagnosis (maybe not MS, or maybe MS + concurrent PNS disease)

CT brain: much less sensitive than MRI; may miss most MS lesions. Only used if MRI is contraindicated (e.g., certain pacemakers, metallic implants).
PET-CT: Further imaging, e.g. PET-CT scan ^[8] — used if malignancy or paraneoplastic syndrome suspected, not routine for MS
CXR: to screen for sarcoidosis (bilateral hilar lymphadenopathy), pulmonary infections

Investigation	Purpose	Key Findings in MS
MRI brain + whole spine with Gd contrast	Demonstrate DIS + DIT; exclude structural causes	Periventricular/juxtacortical/infratentorial/spinal T2 lesions; Gd-enhancing lesions (active); T1 black holes; Dawson's fingers
CSF analysis (LP)	Demonstrate intrathecal IgG synthesis (OCBs); exclude infection	OCBs positive (>90%); mild lymphocytic pleocytosis; normal glucose
Anti-AQP4 Ab	Exclude NMOSD	Negative in MS; positive = NMOSD
Anti-MOG Ab	Exclude MOG-IgG+ disease	Negative in MS; positive = MOGAD
VEP	Detect subclinical optic nerve lesion (DIS)	Prolonged P100 latency
Blood panel (CBC, B12, TFTs, ANA, anti-dsDNA, RPR, HIV)	Exclude mimics	All normal/negative in MS
NCS/EMG	Exclude PNS disease	Normal in MS

A 28-year-old woman presents with left optic neuritis (CIS). How do you diagnose MS?

MRI brain + spine with Gd: shows 3 periventricular T2 lesions + 1 infratentorial T2 lesion → DIS fulfilled (≥ 2 of 4 regions). One lesion enhances with Gd, the others don't → simultaneous Gd+/Gd− lesions → DIT fulfilled.
CSF: OCBs positive (2 bands in CSF not in serum) → also supports DIT.
Blood: Anti-AQP4 negative, anti-MOG negative, ANA negative, B12 normal, RPR non-reactive → mimics excluded.
VEP: Prolonged P100 latency in left eye → confirms optic nerve lesion.

→ DIS ✓ + DIT ✓ + Mimics excluded ✓ → Diagnose MS (RRMS)

NEDA — The Treatment Target

Once diagnosed, the treatment goal is NEDA (No Evidence of Disease Activity) — 4 parameters ^[2]:

No confirmed relapses
No sustained disability progression (measured by EDSS)
No new/enlarging T2 lesions on MRI
No annual brain volume loss > 0.4%

MRI = best biomarker ^[2] for monitoring disease activity. Annual MRI is standard practice.

High Yield Summary — Diagnosis and Investigations

Diagnostic Criteria (2017 McDonald):

DIS: T2 lesions in ≥ 2 of 4 MS-typical regions (periventricular, cortical/juxtacortical, infratentorial, spinal cord)
DIT: ≥ 2 attacks, OR new MRI lesions, OR simultaneous Gd+/Gd− lesions, OR CSF OCBs (2017 addition)
Exclude mimics

PPMS Criteria: ≥ 1 year progressive disability + ≥ 2 of 3 (brain DIS, spinal DIS, CSF OCBs)

Key Investigations:

MRI brain + whole spine with Gd: the single most important test; T2/FLAIR lesions, Gd enhancement, T1 black holes, Dawson's fingers
CSF: OCBs positive in >90% MS (vs ~30% NMOSD); can substitute for DIT
Anti-AQP4 and anti-MOG antibodies: MUST check to exclude NMOSD/MOGAD
VEP: prolonged P100 latency for subclinical optic nerve involvement
Blood tests: exclude mimics (B12, ANA, RPR, HIV, etc.)
NCS/EMG: normal in MS; exclude PNS disease

2017 Updates: Cortical lesions count for DIS; CSF OCBs can substitute for DIT — both enable earlier diagnosis.

Active Recall — MS Diagnostic Criteria and Investigations

References

^[1] Lecture slides: GC 225. Neuroimmunological disorders of the central nervous system.pdf (p8) ^[2] Senior notes: Maksim Medicine Notes.pdf (p262, section on Diagnosis and Investigations) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1277–1279, sections VII Diagnosis) ^[4] Senior notes: Ryan Ho Neurology.pdf (p44, CSF findings) ^[8] Lecture slides: Neurology- Two cases of lower limb weakness.pdf (p24–25, Investigations) ^[16] Lecture slides: Neurology- Two cases of lower limb weakness.pdf (p23, Imaging and neurophysiological tests) ^[17] Lecture slides: Neurology- Two cases of lower limb weakness.pdf (p35, NMO investigations including CSF OCBs comparison)

Management of Multiple Sclerosis

MS management is built on four pillars, each addressing a different aspect of the disease:

Acute relapse management — shorten the duration and severity of an acute attack
Disease-modifying therapy (DMT) — reduce relapse frequency, slow disability accumulation, and suppress new MRI activity
Symptomatic management — treat the symptoms that impair quality of life (spasticity, pain, fatigue, bladder dysfunction)
Rehabilitation and multidisciplinary care — physiotherapy, occupational therapy, psychological support

The overarching treatment target in modern MS care is:

Treatment goal: achieve NEDA (No Evidence of Disease Activity) — 4 parameters ^[2]:

Clinical: no confirmed relapses

Clinical: no sustained disability progression (EDSS: Expanded Disability Status Scale)

Imaging (MRI = best biomarker): no new/enlarging T2 lesions

Imaging: no annual brain volume loss (BVL) > 0.4% ^[2]

The EDSS (Expanded Disability Status Scale) is the standard disability measure in MS, ranging from 0 (normal neurological exam) to 10 (death from MS). Key milestones: EDSS 4.0 = limited walking ability but walks > 500 m without aid; EDSS 6.0 = requires a cane; EDSS 7.0 = wheelchair-bound.

3. Acute Relapse Management

A "relapse" (also called "attack," "exacerbation," or "flare") is defined as:

Otherwise unexplained episodes of focal neurological disturbance > 24 hours with > 30 days of preceding clinical stability ^[4]

This definition is important — a "pseudo-relapse" caused by infection, fever, or heat (Uhthoff's) must be excluded first. Always check for UTI, respiratory infection, or other intercurrent illness before diagnosing a true relapse.

Management of acute MS flare: IV high-dose methylprednisolone (1g daily × 3–7 days) ^[2]

Then short-term (2 weeks) tapering oral prednisolone (e.g. 40 mg → 30 mg → 20 mg → 10 mg) ^[2]
Pulse steroids shorten acute attacks but have no effect in long-term outcome ^[4] — they speed recovery but do NOT prevent the next relapse or slow overall disability progression. Why? Steroids reduce BBB permeability and suppress acute inflammation (oedema, cytokine release), allowing faster resolution of the inflammatory component of the lesion. But they don't prevent the underlying autoimmune process from generating new attacks.
IV has no proven benefit over PO in terms of efficacy ^[4], but IV is traditionally used in acute hospital settings; high-dose oral methylprednisolone (e.g., 500 mg–1 g PO daily) is an acceptable alternative
Not all relapses require treatment — mild sensory relapses with no functional impact may be observed

Severe: may require plasma exchange or IVIG 0.4 mg/kg/day × 5 days ^[2]

Plasmapheresis: used if severe attacks unresponsive to steroids ^[4]
Plasma exchange (PLEX): removes pathogenic antibodies, complement, and cytokines from the circulation. Typically 5–7 exchanges over 10–14 days. Most evidence supports its use in steroid-refractory relapses, particularly those involving severe myelitis or brainstem syndromes.
IVIG (intravenous immunoglobulin): modulates immune response through multiple mechanisms (Fc receptor blockade, anti-idiotypic antibodies, complement inhibition). Less robust evidence than PLEX in MS, but used in practice.

Acute treatment of NMO for comparison: IV methylprednisolone and plasma exchange ^[17] — notably, plasma exchange is used more aggressively and earlier in NMOSD attacks than in MS attacks, because NMOSD relapses tend to be more severe with worse recovery.

4. Disease-Modifying Therapy (DMT)

This is the backbone of long-term MS management. The principle is to suppress the immune-mediated inflammatory process to prevent relapses and delay/prevent disability progression.

Approaches: escalation (most patients) vs induction (for multiple/disabling relapses or extensive MRI) ^[2]

Strategy	Description	When to Use
Escalation	Start with a safer, moderately effective 1st-line DMT; switch to a higher-efficacy DMT if breakthrough disease occurs	Most patients ^[2] — standard approach for typical RRMS
Induction	Start with a high-efficacy DMT from the outset, aiming for rapid and potent disease suppression; may step down later	Multiple/disabling relapses or extensive MRI ^[2] — for aggressive MS at onset

The lecture slide references a publication on the topic: "Aggressive multiple sclerosis: proposed definition and treatment algorithm" ^[18], reflecting the increasing trend toward early aggressive treatment in patients with unfavourable prognostic markers.

Escalation vs Induction — Exam Framing

The traditional approach has been escalation ("start low, go slow"). However, there is growing evidence and expert opinion (including the referenced algorithm from Rush, MacLean, and Freedman) ^[18] supporting early high-efficacy therapy, particularly for patients with poor prognostic features (male sex, motor/cerebellar presentation, high lesion burden, frequent early relapses). The GC slide explicitly cites this concept.

4.2 First-Line DMTs (Moderate Efficacy, Better Safety Profile)

First line ^[2]:

IFN-β 1a/1b: IM injection ^[2]

Property	Detail
Mechanism	IFN-β is a cytokine that shifts the immune response from pro-inflammatory (Th1/Th17) to anti-inflammatory (Th2); reduces T-cell migration across BBB; decreases MHC class II expression on APCs
Formulations	IFN-β1b (Betaferon) — SC every other day; IFN-β1a (Rebif — SC 3×/week; Avonex — IM once/week) ^[4]
Efficacy	↓ relapse rate (~30%), ↓ new MRI lesions in RRMS, ↓ progression in both RRMS and SPMS ^[4]
Side effects	Flu-like illness (myalgia, fatigue, fever), injection site reaction ^[2]; systemic reactions (flushing, chest pain, palpitations, anxiety, dyspnoea) ^[4]
Monitoring	LFTs (can cause hepatotoxicity), CBC, TFTs
Contraindications	Decompensated liver disease; caution in depression (can worsen)

Important Cross-Topic Link

IFN-β is contraindicated in NMOSD — it can worsen attacks. This is one of the key reasons why distinguishing MS from NMOSD before starting treatment is critical. Anti-TNFα agents are also contraindicated in demyelinating diseases including MS ^[19]^[20] — this frequently appears in IBD pharmacology questions.

Teriflunomide (Aubagio): PO QD ^[2]

Property	Detail
Mechanism	Inhibits dihydroorotate dehydrogenase (DHODH) — an enzyme essential for de novo pyrimidine synthesis in rapidly proliferating lymphocytes. Resting/memory lymphocytes use the salvage pathway and are spared.
Administration	Oral, once daily
Efficacy	~30% reduction in relapse rate
Side effects	Headache, nausea/vomiting/diarrhoea, alopecia (hair thinning) ^[2]
Contraindications	Pregnancy (Category X — teratogenic) ^[2]; severe hepatic impairment; concomitant leflunomide
Monitoring	LFTs before and during treatment; BP monitoring
Special consideration	Very long half-life (~2 weeks); requires accelerated elimination procedure (cholestyramine or activated charcoal) if rapid washout is needed (e.g., planning pregnancy)

PO BD dimethyl fumarate ^[4]

Property	Detail
Mechanism	Activates the Nrf2 pathway (nuclear factor erythroid 2-related factor 2) — promotes anti-oxidant and cytoprotective responses; also has immunomodulatory effects (shifts towards Th2, reduces lymphocyte counts)
Administration	Oral, twice daily
Efficacy	~50% reduction in relapse rate; reduces MRI lesion burden
Side effects	Flushing (common, due to prostaglandin release — mitigated by taking with food or aspirin), GI symptoms (nausea, diarrhoea, abdominal pain), lymphopenia
PML risk	Dimethyl fumarate may rarely result in progressive multifocal leukoencephalopathy (PML) ^[4] — risk is very low but necessitates regular lymphocyte monitoring. If lymphocyte count falls <0.5 × 10⁹/L for >6 months, consider stopping.
Monitoring	CBC every 6–12 months; LFTs

SC QD glatiramer acetate (copolymer-1) ^[4]

Property	Detail
Mechanism	Synthetic polypeptide that mimics myelin basic protein (MBP); acts as a decoy antigen that diverts the autoimmune response away from myelin; promotes Th2 anti-inflammatory responses; induces regulatory T cells
Administration	SC injection daily (20 mg) or three times per week (40 mg)
Efficacy	~30% reduction in relapse rate
Side effects	Injection site reactions (most common); post-injection systemic reaction (transient flushing, chest tightness, dyspnoea, palpitations — benign and self-limiting, but can be alarming)
Advantages	Excellent long-term safety profile; safe in pregnancy (one of few DMTs)

4.3 High-Efficacy DMTs (Second-Line or Induction Therapy)

These are reserved for patients with breakthrough disease on first-line agents or for aggressive MS from the outset (induction strategy).

IV q1mo natalizumab ^[4]

Property	Detail
Mechanism	Humanised monoclonal antibody against α4-integrin (VLA-4) — blocks the adhesion molecule on lymphocytes that binds to VCAM-1 on the BBB endothelium. This prevents lymphocytes from crossing the BBB into the CNS. The name: "natal-" (birth/origin) + "-izumab" (humanised monoclonal antibody)
Administration	IV infusion every 4 weeks
Efficacy	Very high: ~68% reduction in relapse rate; ~42% reduction in disability progression
PML risk	Both natalizumab and dimethyl fumarate may rarely result in PML, an opportunistic infection of oligodendrocytes by JC virus. While risk is very low in DMF, the risk is substantial in natalizumab and thus regular MRI monitoring and JC virus Ab should be regularly assayed ^[4]
Risk stratification for PML	Based on three factors: (1) JC virus antibody status and index level, (2) prior immunosuppressant use, (3) duration of natalizumab treatment ( > 2 years increases risk). JCV Ab negative = very low risk; JCV Ab positive with high index + prior immunosuppressant + >2 years therapy = risk up to ~1/100.
Monitoring	JC virus Ab (every 6 months); MRI for PML surveillance (every 3–6 months); infusion reactions
Contraindications	Known PML; immunosuppressed patients; concurrent DMT

Natalizumab and PML — The Major Safety Concern

PML is caused by JC virus reactivation, which infects oligodendrocytes and causes progressive multifocal white matter destruction. It is often fatal or leaves severe disability. The risk is managed by: (1) checking JCV antibody status BEFORE starting natalizumab, (2) if JCV Ab+, considering extended-interval dosing (every 6 weeks instead of 4 weeks), (3) regular MRI surveillance for asymptomatic PML, and (4) stopping natalizumab if JCV index rises or duration exceeds 2 years in high-risk patients. If PML develops, natalizumab is stopped and PLEX may be used to accelerate drug clearance — but this can trigger immune reconstitution inflammatory syndrome (IRIS).

PO fingolimod ^[4] — second-line Tx ^[4]

Property	Detail
Mechanism	Sphingosine-1-phosphate (S1P) receptor modulator — fingolimod is phosphorylated in vivo and then binds to S1P receptors on lymphocytes, causing receptor internalisation. Lymphocytes need S1P signalling to exit lymph nodes; blocking this traps lymphocytes in lymph nodes, preventing them from reaching the CNS. Think of it as "locking the lymphocytes in their barracks."
Administration	Oral, once daily
Efficacy	~54% reduction in relapse rate vs placebo
Side effects	Bradycardia/AV block on first dose (requires 6-hour cardiac monitoring on initiation — because S1P receptors are also on cardiac myocytes); macular oedema; lymphopenia (expected, by mechanism); increased infection risk; elevated LFTs
Contraindications	Recent MI, unstable angina, stroke/TIA, decompensated HF, Mobitz type II or higher AV block (unless pacemaker); concurrent use of Class Ia or III antiarrhythmics; contraindicated in NMOSD
Monitoring	ECG and 6-hour observation on first dose; ophthalmological examination at 3–4 months (macular oedema); CBC; LFTs; VZV serology before initiation (risk of fatal varicella)

Property	Detail
Mechanism	Humanised anti-CD20 monoclonal antibody — targets CD20 on B cells, causing B cell depletion through antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). B cells are now recognised as central to MS pathogenesis: they serve as antigen-presenting cells, produce pro-inflammatory cytokines, and form ectopic meningeal lymphoid follicles.
Administration	IV infusion every 6 months
Efficacy	~46% reduction in relapse rate (RRMS); the ONLY FDA/EMA-approved DMT for PPMS — the ORATORIO trial showed it slowed disability progression in PPMS by ~24%
Side effects	Infusion reactions (premedicate with steroid + antihistamine); increased upper respiratory infections; potential HBV reactivation (see below); theoretically increased malignancy risk (long-term data still being collected)
Monitoring	HBV screening (HBsAg, anti-HBs, anti-HBc) before starting; immunoglobulin levels; infection surveillance
Special note	Closely related to rituximab (anti-CD20) ^[13], which is widely used off-label for MS (cheaper, extensive real-world experience)

Anti-CD20 and HBV Reactivation — Cross-Topic Alert

Rituximab (anti-CD20) and alemtuzumab (anti-CD52) can reactivate occult hepatitis B ^[13]. This is potentially dangerous and fatal ^[13]. Can be FATAL — CL Lai's first case was a 78-year-old lady treated with rituximab who died from fulminant liver failure ^[13].

Before starting any anti-CD20 therapy: screen for HBsAg, anti-HBs, and anti-HBc. If HBsAg+ or anti-HBc+ (even if anti-HBs+): start HBV prophylaxis (entecavir) and monitor HBV DNA. This applies to ocrelizumab, rituximab, and ofatumumab.

Apart from HBV, anti-CD20 and anti-CD52 are also capable of reactivating: CMV, Parvovirus B19, Adenovirus, PCP/PJP ^[13].

IV alemtuzumab ^[4] — second-line Tx ^[4]

Property	Detail
Mechanism	Humanised anti-CD52 monoclonal antibody — CD52 is expressed on the surface of T cells, B cells, monocytes, and NK cells. Alemtuzumab causes profound and prolonged depletion of these cells, followed by gradual immune reconstitution. The immune system "resets," ideally with a more tolerant profile.
Administration	IV infusion: Year 1 = 12 mg/day × 5 consecutive days; Year 2 = 12 mg/day × 3 consecutive days. Additional courses as needed.
Efficacy	Very high: ~55% reduction in relapse rate vs IFN-β1a; significant reduction in disability progression
Side effects	Infusion reactions (very common — premedicate); secondary autoimmunity is the major concern: thyroid disease (~40%, mostly Graves'), immune thrombocytopenia (ITP, ~2%), anti-GBM disease (rare but life-threatening); infections (herpes reactivation — requires aciclovir prophylaxis); listeria meningitis (avoid unpasteurised food)
HA status	Treatment of relapsing-remitting multiple sclerosis, but 3rd line in HA ^[13]
Monitoring	Monthly CBC + creatinine + urinalysis for 4 years after last dose (to detect ITP, anti-GBM); TFTs every 3 months for 4 years; HBV screening
Contraindications	Active infection; HIV; immunosuppression

Property	Detail
Mechanism	Purine nucleoside analogue — preferentially accumulates in lymphocytes (which have high levels of deoxycytidine kinase and low deoxyadenosine deaminase), causing DNA strand breaks and apoptosis. Results in selective, transient lymphocyte depletion.
Administration	Oral — short treatment courses: ~10 days in Year 1 + ~10 days in Year 2, then no treatment needed for Years 3–4 (immune reconstitution therapy)
Efficacy	~58% reduction in relapse rate
Side effects	Lymphopenia (expected); herpes zoster reactivation; potential malignancy risk
Contraindications	Active malignancy; HIV; pregnancy; immunosuppression

Property	Detail
Mechanism	Selective S1P receptor modulator (S1P₁ and S1P₅) — similar principle to fingolimod but more selective
Indication	Active SPMS — the first oral drug approved specifically for SPMS (with active disease)
Key difference from fingolimod	Requires CYP2C9 genotyping before initiation (poor metabolisers need dose adjustment or are contraindicated); shorter half-life

Drug	Route	Mechanism	Efficacy Level	Key Side Effects	Special Considerations
IFN-β	IM/SC	Immunomodulation	Moderate (~30%)	Flu-like, injection site	CI in NMOSD
Glatiramer	SC	Decoy antigen	Moderate (~30%)	Injection site	Safe in pregnancy
Teriflunomide	PO	DHODH inhibition	Moderate (~30%)	GI, alopecia	Teratogenic — Category X
DMF	PO	Nrf2 activation	Moderate-high (~50%)	Flushing, GI, lymphopenia	Low PML risk
Natalizumab	IV	Anti-α4-integrin	High (~68%)	PML	JCV Ab monitoring
Fingolimod	PO	S1P modulator	High (~54%)	Bradycardia, macular oedema	First-dose cardiac monitoring
Ocrelizumab	IV	Anti-CD20	High (~46%)	Infusion reactions, HBV	Only DMT for PPMS
Alemtuzumab	IV	Anti-CD52	Very high (~55%)	Secondary autoimmunity, infections	3rd line in HA; HBV risk
Cladribine	PO	Purine analogue	High (~58%)	Lymphopenia, zoster	Short courses; immune reconstitution
Siponimod	PO	Selective S1P	Moderate-high	Bradycardia, liver injury	For active SPMS; CYP2C9 genotype

This is a high-yield cross-topic point from the surgery/IBD pharmacology lectures:

Anti-TNFα contraindications include: demyelinating disease (Multiple sclerosis), optic neuritis ^[19]^[20]

Why? TNF-α has a paradoxical role in the CNS: while it is pro-inflammatory in the periphery, in the CNS it can have protective/regulatory effects on oligodendrocytes and myelin repair. Anti-TNFα agents can paradoxically worsen or trigger CNS demyelination. Cases of new-onset MS and optic neuritis have been reported in patients receiving infliximab or adalimumab for IBD or rheumatoid arthritis.

High Yield for Exams: If a question asks about contraindications of anti-TNFα, or about drug-induced demyelination, remember: anti-TNFα can worsen/trigger MS and optic neuritis.

MS produces many chronic symptoms that significantly impair quality of life and are not directly addressed by DMTs. Each symptom requires specific management:

Symptomatic Tx ^[4]:

Symptom	Treatments	Mechanism/Rationale
Limb spasticity	Baclofen, BZD (diazepam), dantrolene ^[4]	Baclofen: GABA-B agonist → inhibits spinal reflex arcs. BZDs: enhance GABA-A → central muscle relaxation. Dantrolene: acts directly on skeletal muscle → reduces calcium release from sarcoplasmic reticulum. Intrathecal baclofen pump for severe refractory spasticity. Botulinum toxin for focal spasticity.
Neuropathic pain and trigeminal neuralgia	Carbamazepine, oxcarbazepine, gabapentin, pregabalin, antidepressants ^[4]	Carbamazepine/oxcarbazepine: Na+ channel blockers → first-line for trigeminal neuralgia specifically. Gabapentin/pregabalin: α2δ calcium channel ligands → reduce excitatory neurotransmitter release. Duloxetine/amitriptyline: SNRI/TCA → descending inhibitory pain pathway modulation.
Fatigue	Amantadine, methylphenidate ^[4]	Amantadine: weak NMDA antagonist and dopamine reuptake inhibitor → mechanism in MS fatigue poorly understood but effective in clinical trials. Methylphenidate: CNS stimulant → enhances alertness. Non-pharmacological approaches are first-line: exercise, sleep hygiene, energy conservation strategies, CBT.
Bladder dysfunction	Anticholinergics (oxybutynin, solifenacin) for urgency/frequency; intermittent self-catheterisation for retention; desmopressin for nocturia	Urgency: detrusor hyperreflexia → anticholinergics reduce uninhibited detrusor contractions. Retention: detrusor-sphincter dyssynergia → catheterisation bypasses the dysfunctional sphincter.
Depression	SSRIs (sertraline, fluoxetine), SNRIs, CBT	Very common (~50%); both neurobiological (white matter lesions disrupting mood circuits) and reactive.
Erectile dysfunction	PDE5 inhibitors (sildenafil)	Due to spinal cord autonomic pathway damage.
Tremor	Propranolol, clonazepam, deep brain stimulation (refractory)	Cerebellar tremor is notoriously difficult to treat pharmacologically.
Walking difficulty	Dalfampridine (fampridine, 4-aminopyridine)	K+ channel blocker → restores conduction in demyelinated axons by prolonging the action potential duration. Improves walking speed in ~35% of patients.

MS requires a multidisciplinary approach:

Team Member	Role
Neurologist	Diagnosis, DMT selection, relapse management
MS nurse specialist	Patient education, injection training, relapse triage
Physiotherapist	Mobility, balance, spasticity management, exercise programmes
Occupational therapist	Adaptive strategies, home modifications, vocational rehabilitation
Speech and language therapist	Dysphagia management, communication aids
Psychologist/psychiatrist	Depression, cognitive rehabilitation, adjustment support
Urologist	Complex bladder management
Social worker	Support services, disability benefits

Exercise is increasingly recognised as beneficial in MS — improves fatigue, mood, fitness, and possibly neuroprotection. Moderate aerobic exercise is safe and recommended.

7. Special Considerations

MS relapses tend to decrease during pregnancy (especially 3rd trimester) — likely due to the natural immunosuppressive state of pregnancy (shift toward Th2)
Relapse rate increases in the first 3 months postpartum — immune reconstitution effect
DMT management: most DMTs should be stopped before or during pregnancy
- Glatiramer acetate: considered safest; can be continued
- IFN-β: generally stopped, but may be continued in some cases with discussion
- Teriflunomide: absolutely contraindicated (teratogenic) — requires accelerated elimination before conception
- Natalizumab: may be continued until 3rd trimester if high disease activity
- Anti-CD20 agents: stop ≥ 6 months before conception; check immunoglobulin levels

Live vaccines are generally contraindicated in patients on immunosuppressive DMTs (fingolimod, alemtuzumab, ocrelizumab, cladribine)
VZV serology should be checked before fingolimod; vaccinate if seronegative (at least 4 weeks before starting)
Annual influenza vaccination recommended for all MS patients
COVID-19 vaccination recommended; timing around DMT dosing may affect antibody response (especially with anti-CD20 agents — vaccinate ≥ 4 weeks before next dose if possible)

As emphasised in the hepatology cross-topic link:

Screen all patients for HBV (HBsAg, anti-HBs, anti-HBc) before starting anti-CD20 (ocrelizumab, rituximab), alemtuzumab, or any potent immunosuppressive DMT
HBsAg+ or anti-HBc+ (even occult): start HBV prophylaxis (entecavir) ^[13]

Poor prognostic factors ^[4]:

Demographics: male gender
Symptomatology: motor and cerebellar signs at presentation, multiple MRI cranial lesions
Course: primary progressive, frequent relapses in first 2 years, short interval between first two relapses, poor recovery from relapses

Good prognostic factors: female sex, optic neuritis or sensory symptoms at onset (rather than motor), long interval between first two attacks, few lesions on initial MRI, complete recovery from first relapse.

High Yield Summary — Management of MS

Acute Relapse: IV methylprednisolone 1 g daily × 3–7 days → oral taper. Plasma exchange or IVIG for steroid-refractory severe attacks. Steroids shorten attacks but don't change long-term outcomes.

DMT Strategy: Escalation (most patients: start 1st-line, step up if breakthrough) vs Induction (aggressive MS: start high-efficacy). Goal = NEDA (no relapses, no disability progression, no new MRI lesions, no excessive brain volume loss).

First-line DMTs: IFN-β, glatiramer acetate, teriflunomide, dimethyl fumarate — moderate efficacy, better safety.

High-efficacy DMTs: Natalizumab (PML risk — JCV monitoring), fingolimod (first-dose bradycardia), ocrelizumab (only DMT for PPMS; HBV reactivation risk), alemtuzumab (secondary autoimmunity; 3rd line in HA), cladribine, siponimod (active SPMS).

Critical Safety Points:

Natalizumab → PML (JCV Ab monitoring mandatory)
Anti-CD20 agents → HBV reactivation (screen before starting)
Anti-TNFα → CONTRAINDICATED in MS/demyelinating disease
Teriflunomide → TERATOGENIC
Fingolimod, IFN-β → contraindicated in NMOSD

Symptomatic: Baclofen/BZD for spasticity; carbamazepine for trigeminal neuralgia; amantadine for fatigue; anticholinergics for bladder urgency.

Active Recall — Management of Multiple Sclerosis

References

^[2] Senior notes: Maksim Medicine Notes.pdf (p262, Management section) ^[4] Senior notes: Ryan Ho Neurology.pdf (p138, Treatment and prognostic factors) ^[13] Senior notes: Block A - I am a hepatitis B carrier.pdf (p68, anti-CD20/anti-CD52 and HBV reactivation) ^[17] Lecture slides: Neurology- Two cases of lower limb weakness.pdf (p35, NMO acute treatment) ^[18] Lecture slides: GC 225. Neuroimmunological disorders of the central nervous system.pdf (p45, Aggressive MS treatment algorithm reference) ^[19] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p659, Anti-TNFα contraindications including MS) ^[20] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p673, Anti-TNFα contraindications including MS and optic neuritis)

Complications of Multiple Sclerosis

MS complications arise from two fundamental processes:

The disease itself — cumulative demyelination and axonal loss produce permanent neurological disability across multiple systems
The treatment — immunosuppressive disease-modifying therapies (DMTs) carry their own complications, particularly infections and secondary autoimmunity

The GC lecture slide paints the picture of advanced MS clearly:

In severe patients in advanced stage, permanent neurological disabilities/Sx are common including paraparesis, tetraparesis, spasticity, cerebellar ataxia, fatigue, visual impairment or loss, ataxia, dysphagia, diplopia, oscillopsia, urine retention/incontinence, constipation/bowel incontinence, dysarthria, weak voice, sexual dysfunction, cognitive impairment (cause dementia with cerebral atrophy in young people) ^[1]

Anxiety and depression common in patients with chronic disease and significant disabilities ^[1]

These complications are not random — each one can be traced back to specific anatomical lesions and pathophysiological mechanisms. Let's systematically work through them.

~50% of RRMS patients develop progressive deterioration with accumulation of irreversible neurological disability even without acute attacks/relapses (secondary progressive multiple sclerosis [SPMS]) 10 years after onset (degenerative phase) ^[1]

75% of RRMS go into SPMS ^[2]

This is the single most feared complication of MS. The transition from RRMS to SPMS represents a shift from a predominantly inflammatory process (relapses with recovery) to a predominantly neurodegenerative process (smouldering progression without recovery). The pathological substrate is:

Accumulated axonal transection from repeated inflammatory demyelination events
Chronic microglial activation — "smouldering" plaques with slowly expanding rims of activated microglia cause ongoing low-grade tissue destruction
Mitochondrial dysfunction in demyelinated axons — without myelin, axons must redistribute ion channels across their entire surface; this massively increases energy demand, and if mitochondria cannot keep up, the axon degenerates
Loss of brain reserve — once cumulative neuronal/axonal loss exceeds the brain's capacity to compensate, disability worsens steadily

Poor prognostic factors for disability progression ^[1]^[4]:

Male gender ^[4]
Motor and cerebellar signs at presentation ^[4] — because these indicate damage to functionally critical motor pathways with less potential for compensation compared to sensory pathways
Multiple MRI cranial lesions ^[4]
Primary progressive course ^[4]
Frequent relapses in first 2 years, short interval between first two relapses, poor recovery from relapses ^[4]

2.2 Motor Complications

Paraparesis, tetraparesis, spasticity ^[1]

Pathophysiology: Progressive corticospinal tract demyelination and axonal loss → loss of upper motor neuron inhibition of spinal reflexes → spasticity (velocity-dependent increase in muscle tone), hyperreflexia, clonus, Babinski sign
Clinical impact: Impaired mobility → wheelchair dependence (typically EDSS ≥ 7.0); painful spasms (especially nocturnal flexor spasms); risk of contractures if spasticity is untreated (muscles/tendons shorten permanently)
Secondary complications of immobility: pressure ulcers (decubitus), deep vein thrombosis/pulmonary embolism, osteoporosis, deconditioning

Cerebellar ataxia ^[1]

Pathophysiology: Demyelination of cerebellar peduncles and cerebellar white matter → impaired coordination of voluntary movement
Clinical impact: Gait ataxia → falls → fractures (especially in osteoporotic patients on long-term steroids); intention tremor makes fine motor tasks (eating, writing, dressing) impossible; scanning/staccato dysarthria impairs communication
Cerebellar tremor is notoriously resistant to pharmacological treatment; severe cases may warrant consideration of deep brain stimulation

Visual impairment or loss ^[1]

Pathophysiology: Recurrent optic neuritis → cumulative retinal ganglion cell axonal loss → progressive optic atrophy → permanent visual impairment
Each episode of optic neuritis, even with good initial recovery, causes some degree of retinal nerve fibre layer (RNFL) thinning (measured by OCT)
Bilateral visual loss is less common in MS (more characteristic of NMOSD), but can occur after years of recurrent unilateral episodes affecting alternating eyes
Oscillopsia ^[1]: the subjective sensation of the visual world bouncing or oscillating. Caused by nystagmus (vestibulo-cerebellar pathway lesions or INO) — the brain cannot stabilise the visual image on the retina

2.4 Bulbar Complications

Dysphagia, dysarthria, weak voice ^[1]

Pathophysiology: Brainstem and corticobulbar tract demyelination → impaired coordination of the swallowing reflex
Major risk: Aspiration pneumonia — the most common immediate cause of death in advanced MS. When swallowing is impaired, food/liquid/oral secretions enter the trachea → bacterial colonisation → pneumonia. This can be silent (no cough reflex due to reduced laryngeal sensation).
Management: Speech and language therapy assessment; thickened fluids; nasogastric or PEG tube feeding in severe cases

Aspiration Pneumonia — The Leading Cause of Death in Advanced MS

In advanced MS, the combination of immobility, dysphagia, weak cough (respiratory muscle weakness), and immunosuppressive therapy creates a "perfect storm" for aspiration pneumonia. Vigilant swallowing assessment and proactive respiratory care are essential.

Pathophysiology: Cerebellar dysarthria (scanning speech) from cerebellar lesions; spastic dysarthria from corticobulbar lesions; or mixed
Progressive dysarthria leads to social isolation and communication difficulties

2.5 Autonomic Complications

Bladder dysfunction ( > 90%) ^[2]: urine retention/incontinence ^[1]

Pathophysiology:
- Detrusor hyperreflexia (most common, ~60%): suprasacral spinal cord lesions interrupt descending inhibitory pathways from the pontine micturition centre → uninhibited detrusor contractions → urgency, frequency, urge incontinence
- Detrusor-sphincter dyssynergia (~25%): loss of coordination between detrusor contraction and external sphincter relaxation → the sphincter contracts when the detrusor contracts → incomplete emptying, high post-void residual → risk of urinary tract infections (UTIs)
- Detrusor underactivity (less common): lower spinal cord or cauda equina lesions → flaccid bladder → retention
Complications of bladder dysfunction:
- Recurrent UTIs — the most common infection in MS patients; incomplete bladder emptying provides a reservoir for bacterial growth. UTIs can trigger pseudo-relapses (Uhthoff-like worsening of neurological symptoms from fever/systemic inflammation without new demyelination)
- Urosepsis — ascending UTI → pyelonephritis → sepsis; potentially life-threatening
- Renal impairment — chronic high-pressure detrusor-sphincter dyssynergia can cause vesicoureteral reflux → hydronephrosis → renal damage (long-term)

Constipation/bowel incontinence ^[1]

Pathophysiology: Spinal cord demyelination disrupts autonomic regulation of colonic motility; reduced physical activity further compounds constipation
Constipation can worsen bladder dysfunction (distended rectum compresses the bladder)
Faecal incontinence: less common, due to impaired voluntary sphincter control

Sexual dysfunction ^[1]^[2]

Pathophysiology: Disruption of autonomic sacral pathways (S2–S4); also contributed to by spasticity, fatigue, depression, and medications
Men: erectile dysfunction, anorgasmia
Women: reduced lubrication, anorgasmia, dyspareunia
Often underreported; important to ask about proactively

Cognitive impairment (cause dementia with cerebral atrophy in young people) ^[1]

Prevalence: 40–70% of MS patients have some degree of cognitive impairment
Domains affected: Information processing speed (most common), episodic memory, executive function, visuospatial abilities
Pathophysiology: Brain atrophy of both grey matter and white matter ^[2] → disconnection of cortical-subcortical circuits. Cortical demyelination (now recognised as substantial) directly impairs cortical function. The correlation between cognitive decline and brain atrophy is stronger than the correlation with white matter lesion load.
Progression to dementia: In advanced MS, cognitive impairment can be severe enough to meet criteria for dementia — this is devastating as it occurs in young people who are still of working age
Management: Cognitive rehabilitation; DMTs that reduce brain atrophy may slow cognitive decline; no specific "cognition-enhancing" drug proven effective in MS

Anxiety and depression common in patients with chronic disease and significant disabilities ^[1]

Depression: Lifetime prevalence ~50%. Multifactorial:
- Neurobiological: white matter lesions disrupting frontal-limbic mood circuits; inflammatory cytokines (TNF-α, IL-6) directly affect neurotransmitter metabolism
- Reactive: adjustment to chronic unpredictable disease, loss of independence, social isolation
- Iatrogenic: IFN-β can worsen depression; corticosteroids can cause mood disturbance
Suicide risk: MS patients have a 2–7× higher suicide rate than the general population. This must be actively screened for.
Pseudobulbar affect (pathological laughing/crying): involuntary episodes of crying or laughing disproportionate to the emotional stimulus, caused by brainstem/frontal lesions disrupting motor control of emotional expression. Not the same as depression.
Anxiety: often coexists with depression; also related to unpredictability of relapses

The most common symptom in MS (up to 80%)
Often the most disabling symptom even in patients with minimal physical disability
Pathophysiology: multifactorial — central (axonal damage disrupting neural networks; pro-inflammatory cytokines), peripheral (deconditioning), and psychological (depression, poor sleep)
Worsened by heat (Uhthoff's phenomenon), poor sleep, depression, medications (some DMTs)
Major cause of unemployment and reduced quality of life

Affects ~50–80% of MS patients
Types:
- Neuropathic pain: burning, electric, shooting — from demyelinated sensory pathways
- Trigeminal neuralgia: MS is an important cause of trigeminal neuralgia in young adults (caused by demyelination of the trigeminal root entry zone)
- Lhermitte's symptom: electric shock on neck flexion
- Painful tonic spasms: paroxysmal involuntary muscle contractions
- Musculoskeletal pain: secondary to spasticity, abnormal posture, immobility

In advanced disease, respiratory muscle weakness (from cervical/upper thoracic cord lesions + bulbar dysfunction) → reduced forced vital capacity → hypoventilation → respiratory failure
Combined with impaired cough reflex and dysphagia → aspiration pneumonia (leading cause of death)
Respiratory infections are the most common cause of death in MS patients

Complication	Mechanism
Pressure ulcers	Immobility → sustained pressure on bony prominences → tissue ischaemia → skin breakdown (sacrum, heels, trochanters)
DVT / PE	Immobility + spastic limbs → venous stasis → thrombosis. MS patients have a 2–3× higher VTE risk.
Osteoporosis	Immobility, recurrent corticosteroid courses, vitamin D deficiency → reduced bone mineral density → fractures (especially vertebral, hip)
Falls and fractures	Ataxia, spasticity, sensory loss, visual impairment → increased fall risk; osteoporosis compounds fracture risk
Deconditioning	Reduced physical activity → muscle atrophy, cardiovascular deconditioning → worsened fatigue and disability (vicious cycle)

The DMTs used to treat MS carry their own significant complications, and these are frequently examined:

Treatment	Infection Risk	Mechanism
Natalizumab	PML (progressive multifocal leukoencephalopathy) ^[4]	Blocks lymphocyte trafficking to CNS → JC virus reactivates in immunologically "unmonitored" brain. Risk up to ~1/100 in high-risk patients (JCV Ab+, prior immunosuppression, > 2 years therapy)
Rituximab / Ocrelizumab (anti-CD20)	HBV reactivation (potentially fatal fulminant liver failure) ^[13]; CMV, Parvovirus B19, Adenovirus, PCP/PJP ^[13]	B-cell depletion → impaired humoral immunity → loss of viral immune surveillance
Alemtuzumab (anti-CD52)	Herpes reactivation, listeria meningitis; also HBV reactivation ^[13]; CMV, PCP/PJP ^[13]	Profound pan-lymphocyte depletion → prolonged immunosuppression
Fingolimod	VZV reactivation (zoster), cryptococcal meningitis, PML (rare)	Lymphocyte sequestration in lymph nodes → lymphopenia
DMF	PML (very rare, only in setting of severe sustained lymphopenia)	Sustained lymphopenia if unchecked
Cladribine	Herpes zoster reactivation	Selective lymphocyte depletion
Corticosteroids (acute relapses)	Opportunistic infections, hyperglycaemia, adrenal suppression	Broad immunosuppression; metabolic effects

PML — The Most Feared Treatment Complication

PML (from JC virus) causes progressive, multifocal white matter destruction. It presents with progressive cognitive decline, visual loss, hemiparesis, and ataxia — which can initially mimic an MS relapse. MRI shows large, confluent, non-enhancing white matter lesions that do NOT respect vascular territories and tend to involve the subcortical U-fibres. Diagnosis: JC virus PCR in CSF. If PML is suspected on natalizumab: stop drug immediately; consider PLEX to accelerate drug clearance; monitor for immune reconstitution inflammatory syndrome (IRIS) as immune cells flood back into the CNS. Mortality is ~20–30%, and most survivors have significant disability.

Thyroid disease (~40%): mostly Graves' disease (hyperthyroidism); also Hashimoto's. Why? Immune reconstitution after profound depletion may produce autoreactive T cells that recognise thyroid antigens.
Immune thrombocytopenia (ITP) (~2%): autoantibodies against platelets → bleeding risk
Anti-GBM disease (Goodpasture's syndrome) (rare, < 1%): autoantibodies against the glomerular basement membrane → rapidly progressive glomerulonephritis ± pulmonary haemorrhage. Can be fatal if not detected early.
Requires monthly monitoring (CBC, creatinine, urinalysis) for 4 years after last dose; TFTs every 3 months for 4 years [from Management section]

First-dose bradycardia / AV block: S1P receptors are expressed on cardiac myocytes; fingolimod causes transient negative chronotropic effect on first dose. Usually asymptomatic but can cause symptomatic bradycardia or rarely complete heart block. Requires 6-hour cardiac monitoring on first dose.
Macular oedema: S1P receptor modulation affects retinal vasculature → fluid accumulation → visual blurring (3–4 months after starting)

Teriflunomide: Category X — absolutely contraindicated in pregnancy. Long half-life requires accelerated elimination procedure (cholestyramine/activated charcoal) before conception
Fingolimod, cladribine, methotrexate: all teratogenic; require reliable contraception and washout period before pregnancy

Stage	Typical Complications
Early RRMS (0–5 years)	Optic neuritis (visual loss), sensory symptoms, fatigue, depression, anxiety, relapse-related disability (usually reversible)
Established RRMS (5–15 years)	Accumulating residual deficits after incomplete relapse recovery; cognitive impairment beginning; bladder dysfunction; treatment-related complications (PML, infections)
Transition to SPMS (10–20 years)	Progressive spastic paraparesis, cerebellar ataxia, cognitive decline, progressive visual loss, worsening autonomic dysfunction
Advanced MS (> 15–20 years)	Paraparesis/tetraparesis, wheelchair dependence, dysphagia with aspiration risk, dementia, pressure ulcers, recurrent infections (UTI, pneumonia), DVT/PE, osteoporotic fractures

MS reduces life expectancy by approximately 7–14 years compared to the general population. The major causes of death are:

Infections — especially aspiration pneumonia and urosepsis (related to immobility, dysphagia, bladder dysfunction, immunosuppressive therapy)
Respiratory failure — from respiratory muscle weakness in advanced disease
Cardiovascular disease — increased risk (immobility, deconditioning; some evidence of accelerated atherosclerosis)
Suicide — 2–7× general population risk; related to depression, disability, hopelessness
Treatment-related — PML, opportunistic infections, secondary autoimmunity complications

High Yield Summary — Complications of MS

Disease Progression: ~50% RRMS → SPMS by 10 years; 75% eventually. Progressive irreversible disability driven by axonal loss and neurodegeneration.

Motor: Spastic paraparesis → tetraparesis → wheelchair dependence; cerebellar ataxia → falls/fractures; contractures from untreated spasticity.

Visual: Recurrent optic neuritis → progressive optic atrophy → visual impairment/loss; oscillopsia from nystagmus/INO.

Bulbar: Dysphagia → aspiration pneumonia (leading cause of death); dysarthria → communication failure.

Autonomic: Bladder dysfunction ( > 90%) → recurrent UTIs → urosepsis; bowel dysfunction; sexual dysfunction.

Cognitive: 40–70% have cognitive impairment; can progress to dementia with brain atrophy in young people.

Psychiatric: Depression (~50%); 2–7× higher suicide rate; pseudobulbar affect; anxiety.

Secondary Complications of Disability: Pressure ulcers, DVT/PE, osteoporosis, falls/fractures, deconditioning.

Treatment Complications: PML (natalizumab > dimethyl fumarate); HBV reactivation (anti-CD20, anti-CD52); secondary autoimmunity (alemtuzumab — thyroid, ITP, anti-GBM); first-dose bradycardia (fingolimod); teratogenicity (teriflunomide).

Causes of Death: Aspiration pneumonia, respiratory failure, urosepsis, cardiovascular disease, suicide, treatment-related infections.

Active Recall — Complications of Multiple Sclerosis

References

^[1] Lecture slides: GC 225. Neuroimmunological disorders of the central nervous system.pdf (p3, Clinical Features; p15, Poor prognostic factors) ^[2] Senior notes: Maksim Medicine Notes.pdf (p261, section 11.8 CNS demyelinating diseases — clinical features and brain atrophy) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1272–1274, disease patterns and progression) ^[4] Senior notes: Ryan Ho Neurology.pdf (p138, prognostic factors and treatment complications) ^[13] Senior notes: Block A - I am a hepatitis B carrier.pdf (p68, anti-CD20/anti-CD52 and HBV/infection reactivation risks)