What is Multiple Sclerosis (MS)?

What is Multiple Sclerosis (MS)?

Multiple sclerosis is a chronic, inflammatory, autoimmune disease of the central nervous system that causes widespread focal degradation of the myelin sheath, variable axonal and neuronal injury, and progressive disability in young adults. 1

Disease Pathophysiology

MS is characterized by inflammatory demyelination with axonal transection, where the immune system attacks the protective myelin covering of nerve fibers in the brain and spinal cord. 2 The disease results from a complex interplay of genetic, immunological, and environmental factors, though the exact cause remains unknown. 1

The pathological process involves:

• Acute focal inflammation causing demyelinating lesions that manifest as clinical relapses 3
• Chronic diffuse neurodegeneration occurring independently of acute inflammation, driven by disseminated activated microglial-like inflammatory cells throughout the CNS 3
• Axonal damage and neuronal injury that accumulates over time, leading to irreversible disability 2

Clinical Subtypes

MS presents in distinct clinical patterns that determine prognosis and treatment approach:

Relapsing-Remitting MS (RRMS)

• Accounts for approximately 85% of cases at onset 1, 4
• Characterized by acute neurological symptoms developing over hours to days, followed by periods of remission 4
• During relapses, nerve impulse conduction along axons is affected during acute inflammatory phases but tends to improve with healing during remission 1
• Over time, relapses cause extensive myelin damage with progressive loss of neuronal function 1

Primary Progressive MS (PPMS)

• Affects approximately 15% of cases 1, 4
• Characterized by steadily increasing neurological disability from disease onset without distinct relapses or remissions 1, 4
• Often presents as progressive myelopathy 4
• Pathogenesis involves progressive neurological damage rather than the relapse-remission pattern 1

Secondary Progressive MS (SPMS)

• Develops when RRMS patients transition to a pattern of steadily increasing neurologic disability following the initial relapsing course 2
• The majority of RRMS patients eventually progress to this form 5

Typical Clinical Presentations

MS typically presents in young adults with a mean age of onset between 20-30 years, affecting women nearly three times more frequently than men. 2 Common initial presentations include:

• Unilateral optic neuritis (inflammation of the optic nerve causing vision loss) 4, 2
• Partial myelitis (spinal cord inflammation) 4, 2
• Sensory disturbances including numbness and tingling 4, 2
• Diplopia (double vision) 4
• Internuclear ophthalmoplegia (eye movement disorder) 4, 2
• Balance and gait dysfunction 4

Epidemiology and Impact

MS affects approximately 900,000 people in the United States and nearly 2.8 million people worldwide. 2, 5 The prevalence ranges from 5 to 300 per 100,000 people globally, with higher rates at higher latitudes. 2

Life expectancy is reduced compared to the general population (75.9 vs 83.4 years). 2 The disease leads to physical disability, cognitive impairment, and significantly decreased quality of life. 2

Associated Complications

Patients with MS commonly experience:

• Weight loss, malnutrition, and cachexia due to reduced mobility, fatigue, inappropriate diet, physical difficulty eating or drinking, poor appetite, poor sight, reduced cognition, and dysphagia 1
• Weakness and imbalance 6
• Visual abnormalities 6
• Changes in cognition 6
• Bladder and sexual dysfunction 6
• Spasticity and fatigue 4

Diagnostic Approach

Diagnosis requires objective demonstration of CNS lesions disseminated in both time and space, integrating MRI with clinical findings while excluding alternative diagnoses. 4, 7 At least one clinical event consistent with acute demyelination is essential—diagnosis cannot be made on MRI alone. 4, 8

The diagnosis applies best to individuals aged 10-59 years with typical presentations. 4, 8 Outside this age range or with atypical presentations, additional caution and supporting evidence from CSF analysis and visual evoked potentials may be needed. 8, 7