Pathogenesis

The natural course of MS is highly variable, usually spanning two or three decades. Figure 1 illustrates the key aspects of the natural history of MS in terms of clinical course, pathology and MRI activity. Note particularly the pathology section of the diagram, which illustrates how axonal loss begins during the very earliest, pre-clinical stages of the disease and becomes steadily worse throughout its course.1

Figure 1. Natural history of MS illustrated in terms of clinical course, pathology and MRI activity. << insert figure>>

Approximately 85% of patients with MS experience a relapsing–remitting phase of MS (RRMS) initially.2,3 As time progresses, the degree of recovery between relapses lessens and disability begins to accumulate until the disease enters the secondary-progressive phase (SPMS). The four types of MS are generally considered as follows:

A. Relapsing–remitting MS

  • Most common form of MS. 
  • Attacks and remissions occur over time with periods of stability in between.  
  • A majority (up to 85%) of people with MS start with this type.       

B. Secondary-progressive MS

  • Attacks are less common.  
  • Symptoms and disability continue to worsen.        

C. Primary-progressive MS (PPMS)

  • Steadily worsens from the beginning of the disease without relapses.       

D. Benign MS

  • Mild infrequent sensory exacerbations with full recovery.    
  • This form of MS does not worsen with time and there is no permanent disability or disease progression.  

References:
1. Dhib-Jalbet S, McFarlin DE. Immunology of multiple sclerosis. Ann Allergy 1990; 64: 433-44.
2. French-Constant C. Pathogenesis of multiple sclerosis. Lancet 1994.; 343(8892): 271-5.
3. Ferguson B, Matyszak MK, Esiri MM, et al. Axonal damage in acute multiple sclerosis lesions. Brain 1997; 120(Pt 3): 393-9.

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