Multiple Sclerosis – etiology, pathogenesis, and clinical manifestations.
Multiple sclerosis is a chronic, autoimmune demyelinating disease of the central nervous system (CNS) characterized by focal areas of demyelination (plaques), inflammation, and neurodegeneration, leading to varied neurological symptoms.
Etiology (Causes)
- 1 Genetic factors
- Strong association with certain HLA class II alleles, especially HLA-DRB1*1501.
- Familial clustering; increased risk in first- degree relatives.
- 2 Environmental factors
- Higher prevalence in temperate climates (farther from equator).
- Vitamin D deficiency (low sunlight exposure).
- Viral infections (e.g., Epstein-Barr virus [EBV]) — thought to trigger or modulate immune response.
- 3 Autoimmune mechanisms
- Loss of immune tolerance → autoreactive T cells against myelin antigens.
Pathogenesis
- 1 Autoimmune attack on CNS myelin
- Activation of CD4+ T helper cells (especially Th1 and Th17 subsets) that cross the blood- brain barrier.
- T cells recognize myelin antigens → release pro-inflammatory cytokines (IFN- γ, IL- 17, TNF- α).
- 2 Recruitment of other immune cells
- Macrophages and microglia become activated → phagocytose myelin and oligodendrocytes.
- B cells produce autoantibodies against myelin components → further demyelination.
- 3 Formation of demyelinating plaques
- Focal areas of myelin loss (plaques), especially in:
- Optic nerves (optic neuritis).
- Periventricular white matter.
- Brainstem and spinal cord.
- 4 Axonal damage and neurodegeneration
- Progressive axonal loss contributes to chronic disability and irreversible neurological deficits.
Clinical Manifestations
Typical onset
- Age: 20–40 years.
- More common in women ( female:male ≈ 2:1).
Common initial symptoms
- Optic neuritis: painful vision loss in one eye, decreased visual acuity.
- Sensory disturbances: paresthesias ("pins and needles"), numbness.
- Motor weakness: often asymmetric limb weakness.
Other manifestations
- Internuclear ophthalmoplegia (impaired horizontal eye movements) due to brainstem lesions.
- Ataxia and balance problems (cerebellar involvement).
- Spasticity and hyperreflexia (upper motor neuron signs).
- Lhermitte’s sign: electric shock- like sensation down the spine on neck flexion.
- Bladder dysfunction: urgency, incontinence.
- Fatigue: common, can be severe.
- Cognitive impairment: memory, attention difficulties in later stages.
Disease course patterns