Multiple Sclerosis — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Multiple sclerosis (MS) is a chronic immune-mediated disease of the central nervous system (CNS) characterised by demyelination (damage to the myelin sheaths surrounding nerve axons) and neurodegeneration in the brain, spinal cord, and optic nerves. It is the most common cause of non-traumatic neurological disability in young adults in high-income countries, affecting approximately 2.8 million people worldwide. Onset typically occurs between ages 20 and 40, with a 2:1 female predominance. MS is classified by clinical course: relapsing-remitting MS (RRMS) — the most common form (85-90% of initial diagnoses), characterised by discrete episodes of neurological dysfunction (relapses) followed by full or partial recovery; secondary progressive MS (SPMS) — evolving from RRMS over 10-20 years with progressive worsening with or without superimposed relapses; primary progressive MS (PPMS) — affecting 10-15%, predominantly older males, with gradual worsening from onset without discrete relapses; and progressive relapsing MS (PRMS). The McDonald Criteria (2017 revision) provide the diagnostic framework based on clinical lesions disseminated in space and time, supported by MRI and cerebrospinal fluid findings.

MS results from a complex interplay of genetic susceptibility and environmental factors that trigger an aberrant immune response targeting CNS myelin. The strongest genetic association is with HLA-DRB1*15:01 (approximately doubles risk) — over 200 additional genetic variants have been identified but each contributes modestly. Concordance in identical twins is 25-30%, confirming the importance of environmental factors. Environmental risk factors with strong evidence include: Epstein-Barr virus (EBV) infection, particularly infectious mononucleosis — a 2022 landmark cohort study in US military personnel demonstrated a 32-fold increased risk of MS after EBV infection, strongly implicating EBV as a necessary — but not sufficient — trigger; low vitamin D levels (lower latitude/sunlight exposure — MS is significantly more prevalent in Northern Europe, Canada, and New Zealand than tropical regions); cigarette smoking (doubles MS risk and accelerates disability progression); childhood obesity; and low exposure to sunlight independent of vitamin D. MS is more prevalent at higher latitudes (latitude gradient): affects 100-200 per 100,000 in Northern Europe versus under 5 per 100,000 near the equator. Migration studies show that people migrating from high-risk to low-risk regions before puberty acquire the lower risk of the destination country, implicating childhood environmental exposure.

MS can cause diverse neurological symptoms depending on the location of demyelinating lesions. Common presenting features include: optic neuritis (painful unilateral visual loss or blurring — often the first manifestation in 25% of patients; colour vision loss and relative afferent pupillary defect); limb weakness (upper motor neurone pattern — spastic weakness, increased reflexes, extensor plantar responses); sensory disturbances (numbness, tingling, 'band-like' tightness around the trunk — MS hug, electric shock sensation down the spine with neck flexion — Lhermitte's sign); cerebellar ataxia (coordination problems, gait instability, intention tremor, nystagmus, dysarthria — DANISH mnemonic: Dysdiadochokinesis, Ataxia, Nystagmus, Intention tremor, Scanning speech, Hypotonia); brainstem symptoms (diplopia from internuclear ophthalmoplegia — medial longitudinal fasciculus lesion causing inability to adduct one eye; vertigo, dysphagia, facial numbness); bladder dysfunction (urgency, frequency, incomplete emptying — affects 75% of MS patients); bowel dysfunction; sexual dysfunction; and cognitive impairment (processing speed, working memory — 'cog fog' — affects 40-70%). Fatigue is the most prevalent symptom, affecting 80% of patients and often the most disabling. Uhthoff's phenomenon: temporary symptom worsening with heat (exercise, hot bath, fever) — pathognomonic of MS and caused by temperature-dependent conduction block in demyelinated axons.

The McDonald Criteria (2017) require clinical or MRI evidence of CNS lesions disseminated in space and time, with all alternative diagnoses excluded. MRI is the cornerstone investigation: brain MRI with gadolinium contrast identifies white matter lesions characteristic of MS — periventricular (Dawson's fingers — lesions perpendicular to the ventricles), juxtacortical, infratentorial, and spinal cord plaques. Active inflammation shows gadolinium enhancement (blood-brain barrier breakdown). Lesions disseminated in space (two or more typical locations) and disseminated in time (active and inactive lesions coexisting, or new lesion on follow-up MRI) support the diagnosis. Spinal cord MRI identifies cord lesions causing myelopathy. Cerebrospinal fluid (CSF) analysis via lumbar puncture: oligoclonal bands (IgG) in CSF but not serum are present in 85-95% of MS patients and support the diagnosis when MRI criteria are not fully met. Evoked potentials (visual, somatosensory, brainstem) demonstrate subclinical demyelination in additional pathways. AQP4-IgG and MOG-IgG antibodies must be checked to exclude neuromyelitis optica spectrum disorder (NMOSD) and MOGAD — conditions that mimic MS but require different treatment. Vitamin B12, thyroid function, and ANA/ENA are checked to exclude mimics.

MS treatment encompasses acute relapse management, disease-modifying therapies (DMTs) to reduce relapse rate and disability progression, and symptomatic management. Acute relapses: high-dose IV or oral methylprednisolone (1g daily for 3-5 days) shortens relapse duration but does not alter long-term disability; plasma exchange for severe steroid-refractory relapses. Disease-modifying therapies: the current paradigm favours early high-efficacy therapy. Platform/moderate-efficacy DMTs include: interferon-beta (subcutaneous or IM injections), glatiramer acetate (subcutaneous), dimethyl fumarate (oral), teriflunomide (oral), and siponimod (oral for SPMS). High-efficacy DMTs: natalizumab (IV infusion monthly — anti-VLA4, prevents lymphocyte entry into CNS — 68% reduction in relapse rate; JC virus antibody monitoring required for PML risk); ocrelizumab (IV infusions every 6 months — anti-CD20 B-cell depletion — approved for RRMS and PPMS); ofatumumab (subcutaneous anti-CD20 monthly); cladribine (oral lymphocyte-depleting tablets over 2 years — 58% relapse reduction); alemtuzumab (IV infusion — potent lymphocyte depletion — most effective but highest risk profile; secondary autoimmunity in 40%). Haematopoietic stem cell transplantation (HSCT) for highly active RRMS unresponsive to DMTs achieves long-term remission in 70-80%. Symptomatic management: fampridine (4-aminopyridine) for walking speed; baclofen or tizanidine for spasticity; amantadine or modafinil for fatigue; oxybutynin or solifenacin for bladder urgency; pregabalin or amitriptyline for neuropathic pain; physiotherapy and rehabilitation are fundamental.

Untreated relapsing-remitting MS accumulates neurological disability from incompletely recovered relapses — each relapse causing permanent axonal injury. After 15-20 years, 50% of RRMS patients convert to secondary progressive MS (SPMS) with continuous disability accumulation. Disability encompasses walking impairment (50% need an aid after 15 years), upper limb dysfunction, cognitive impairment (40-70%), fatigue (most prevalent symptom, affecting 80%), bladder dysfunction, chronic pain, and depression. Complications of immobility — pressure ulcers, deep vein thrombosis, aspiration pneumonia — affect advanced MS. Disease-modifying therapies (interferons, natalizumab, ocrelizumab, cladribine) reduce relapse rate by 30-80% and substantially delay disability accumulation when started early in the disease course.

Primary prevention of MS is not yet established, but modifiable risk reduction includes: maintaining adequate vitamin D levels (supplementation to achieve serum 25-OH vitamin D above 75 nmol/L, particularly in Northern latitudes); smoking cessation (reduces MS risk by 50% and slows disability progression in established MS); maintaining healthy weight. EBV vaccination, if developed, could potentially reduce MS incidence significantly based on current evidence. For established MS, consistent adherence to prescribed DMT is the most important modifiable factor — missing doses or discontinuing treatment markedly increases relapse risk. Avoid known infection triggers of relapses — prophylactic vaccination is recommended (inactivated vaccines are safe; live vaccines should be discussed with the neurologist, particularly during high-efficacy immunosuppressive therapy). Temperature management: avoid overheating during exercise (cold vest, cool environment), monitor during fever. Maintain regular aerobic exercise and physiotherapy — exercise improves fatigue, balance, mood, and quality of life and does not worsen MS. Smoking cessation is strongly advised in established MS as it accelerates conversion to secondary progressive disease.

Seek urgent neurological assessment for: new or worsening neurological symptoms lasting more than 24 hours (possible MS relapse or new lesion requiring IV methylprednisolone); sudden visual loss or significant blurring in one eye (optic neuritis — urgent ophthalmology and neurology referral); sudden inability to walk or rapidly worsening leg weakness (myelitis — emergency MRI needed); severe vertigo or double vision of sudden onset. Contact your MS nurse or neurologist promptly for: any new symptoms not previously experienced, significant fatigue worsening, bladder or bowel changes, or symptoms that may indicate a relapse. Seek emergency care for: high fever combined with significantly worsening existing MS symptoms (pseudorelapse from Uhthoff's/fever — must exclude true relapse); and any signs of natalizumab-related PML (progressive multifocal leukoencephalopathy) — new or worsening cognitive changes, weakness, or vision changes in patients on natalizumab.