Multiple Sclerosis: Causes, Symptoms, Diagnosis and Treatment — Overview, Diagnosis & Treatment Options | MyMedicPlus

Multiple sclerosis (MS) is a chronic, immune-mediated, demyelinating and neurodegenerative disease of the central nervous system (CNS), characterized by inflammation, demyelination, axonal damage, and gliosis in the brain, spinal cord, and optic nerves. It is the most common non-traumatic cause of neurological disability in young adults, affecting approximately 2.9 million people worldwide, with highest prevalence in Northern Europe, North America, and Australia. MS most commonly presents between ages 20–40 and affects women 2–3 times more often than men. Clinical courses include relapsing-remitting MS (RRMS, ~85% at onset: discrete attacks with partial/complete recovery), secondary progressive MS (SPMS: progressive disability accrual after an initial relapsing course), primary progressive MS (PPMS: gradual deterioration from onset without relapses; ~15%; more equal sex ratio), and clinically isolated syndrome (CIS: first demyelinating episode, with high risk of conversion to MS if MRI criteria met). The diagnosis is established by the 2017 McDonald Criteria, integrating clinical, MRI, and CSF findings to demonstrate lesion dissemination in space and time.

MS is a complex, multifactorial disease resulting from the interaction of genetic susceptibility and environmental triggers leading to autoreactive T-cell and B-cell mediated destruction of myelin sheaths. The strongest genetic risk factor is HLA-DRB1*15:01 (HLA-DR2), which approximately doubles MS risk; over 200 additional susceptibility loci have been identified by GWAS. Environmental and lifestyle risk factors include: EBV infection — recent Mendelian randomization and longitudinal military cohort studies (Bjornevik et al., Science 2022) provide strong evidence that prior EBV infection is necessary (though not sufficient) for MS development; vitamin D deficiency — low 25-hydroxyvitamin D levels are associated with higher relapse rates and disability progression; cigarette smoking — doubles MS risk and accelerates disability progression; obesity in adolescence (BMI >27 at age 18 doubles risk in females); and latitude gradient (higher prevalence in temperate zones than equatorial regions) partially explained by sun exposure and vitamin D. Shift work (disrupting circadian rhythm) and comorbid autoimmune diseases are additional risk factors.

MS symptoms vary widely depending on the location and severity of demyelinating lesions. Common presenting symptoms include: optic neuritis (unilateral painful vision loss, color desaturation, relative afferent pupillary defect — the most common CIS presentation, in 25% of cases); transverse myelitis (bilateral limb weakness, sensory loss below a spinal level, urinary retention or incontinence); internuclear ophthalmoplegia (lateral gaze diplopia from MLF demyelination); sensory symptoms (paresthesia, dysesthesia, band-like tightening — 'MS hug'); cerebellar ataxia and intention tremor; and Lhermitte's phenomenon (electric shock sensation radiating down the spine on neck flexion — almost pathognomonic of MS). Uhthoff's phenomenon (symptom worsening with heat or exercise due to impaired conduction in demyelinated axons) is highly characteristic. Fatigue — the most common MS symptom overall, in 80–90% — is debilitating, interferes with employment, and is distinct from sleep-related fatigue. Cognitive impairment (information processing speed, memory, executive function) affects 40–70%. Depression affects 50% of patients over their lifetime.

The 2017 McDonald Criteria require demonstration of CNS demyelination disseminated in space (DIS) and time (DIT), fulfilled clinically, by MRI, or by CSF analysis. MRI brain and spinal cord with gadolinium is the cornerstone investigation: periventricular (Dawson's fingers — perpendicular to the corpus callosum on FLAIR), juxtacortical, infratentorial, and spinal cord lesions on T2/FLAIR define DIS; gadolinium-enhancing lesions (active inflammation) or new T2 lesions on follow-up MRI define DIT. A single MRI meeting both DIS and DIT criteria satisfies McDonald criteria even for a CIS. Lumbar puncture for CSF analysis: oligoclonal bands (OCBs) in CSF but not serum (intrathecal IgG synthesis) are present in >90% of MS patients and may satisfy DIT criterion; elevated IgG index; mild pleocytosis. Visual evoked potentials (VEP) demonstrate delayed P100 latency in optic neuritis. Key differential diagnoses to exclude: neuromyelitis optica spectrum disorder (NMOSD — anti-AQP4 and anti-MOG antibody testing mandatory), CNS vasculitis, neurosarcoidosis, and inherited leukodystrophies.

MS management is multimodal: acute relapse treatment, long-term disease-modifying therapy (DMT), and symptomatic management. Acute relapses causing functional deficit: high-dose methylprednisolone 1g IV for 3–5 days hastens recovery (does not affect long-term outcome). DMTs are classified by efficacy and risk. Low-to-moderate efficacy: interferon-beta (1a, 1b), glatiramer acetate, teriflunomide, dimethyl fumarate — reduce annualized relapse rate (ARR) by 30–50%; appropriate for mild/moderate RRMS. High-efficacy DMTs (recommended early for active disease, especially by AAN 2021 and NICE 2022 MS guidelines): natalizumab (anti-VLA4, 68% ARR reduction; JC virus monitoring mandatory); ocrelizumab (anti-CD20 B-cell depletion, 46–47% ARR reduction over interferon; only approved agent for PPMS per ORATORIO trial); ofatumumab, ublituximab (subcutaneous anti-CD20); cladribine, alemtuzumab (for highly active RRMS; significant immune reconstitution). Autologous haematopoietic stem cell transplantation (aHSCT) is a high-efficacy option for young patients with active RRMS failing high-efficacy DMTs. Symptomatic treatment: baclofen/tizanidine (spasticity), amantadine/modafinil (fatigue), dalfampridine (walking), oxybutynin (urinary urgency), venlafaxine (neuropathic pain), and specialist rehabilitation.

The prognosis of multiple sclerosis is highly variable and depends on clinical course, disease activity, and treatment response. MS itself is rarely directly fatal, and most patients have a near-normal life expectancy with modern care — estimated median reduction in life expectancy is 7–14 years, primarily due to complications (infections, immobility-related disease, depression, and suicide) rather than the disease process itself. RRMS treated with high-efficacy DMTs (natalizumab, ocrelizumab, alemtuzumab, aHSCT) significantly reduces annual relapse rates by 50–70%, slows disability progression, and reduces MRI lesion accumulation. Predictors of more benign long-term outcome include female sex, younger age of onset (<30 years), purely sensory or optic neuritis onset, low relapse frequency, and minimal disability at 5 years. Predictors of worse prognosis include progressive disease course from onset, motor or sphincter involvement early in the disease, high lesion burden on initial MRI, older age at onset, and male sex. Approximately 50% of RRMS patients convert to secondary progressive MS over 25 years without high-efficacy DMT intervention; this rate is substantially reduced with early aggressive treatment. PPMS has a slower but relentless progressive disability trajectory — ocrelizumab modestly slows progression (ORATORIO trial). The Expanded Disability Status Scale (EDSS) is the standard outcome measure; patients reaching EDSS 6 (walking aid required) in a mean of 15–20 years without effective treatment — early high-efficacy DMT substantially delays this milestone and preserves quality of life.

There is currently no proven strategy to prevent MS onset in the general population. Modifiable risk factor reduction is recommended: vitamin D supplementation to achieve serum 25-OHD >50 nmol/L is associated with lower relapse rates and is recommended in patients with insufficiency or deficiency; smoking cessation reduces relapse risk and slows disability progression; healthy BMI maintenance; and avoidance of severe infections (particularly EBV, though vaccination against EBV is in development). Sun exposure with appropriate sun protection is recommended to balance vitamin D synthesis risk reduction and melanoma risk. First-degree relatives of MS patients (lifetime risk ~2–3%, vs 0.25% general population) are advised to maintain adequate vitamin D, not smoke, and report early neurological symptoms for urgent investigation. Ongoing clinical trials are evaluating whether DMT initiation at the CIS stage before full McDonald criteria for MS are met reduces disability accrual — early initiation is associated with improved outcomes per ECTRIMS/EAN guidelines.

Seek urgent neurological review (within 2 weeks) for: sudden visual loss or blurred vision with eye pain (optic neuritis); bilateral limb weakness or sensory disturbance with bladder symptoms suggesting transverse myelitis; new vertigo, diplopia, or balance disturbance lasting more than 24 hours; or any new focal neurological deficit in a young adult. Do not attribute young adult sensory symptoms, visual changes, or balance problems to stress, anxiety, or 'functional' causes without MRI of brain and spinal cord and neurology review — delayed diagnosis by years is common. Patients with a diagnosis of MS should seek urgent review for acute relapses — IV methylprednisolone should be initiated within 48 hours of severe relapse onset to maximize recovery. Report any new lower limb weakness or urinary retention immediately, as transverse myelitis may be an MS relapse requiring emergency MRI and treatment.