Primary progressive multiple sclerosis (PPMS) is the least common MS disease course, affecting only about 10-20% of people with MS. For this reason, the natural history has been difficult to investigate. Understanding the characteristic natural history of a disease enables physicians to anticipate prognosis and identify opportunities for prevention and control.

PPMS differs from the more common relapsing–remitting MS (RRMS) in several key aspects:

  • It begins later in life with a median onset age around 40 years, versus 30 in RRMS
  • It proportionally affects more men
  • The mechanisms underlying the disease are believed to be different
  • In PPMS inflammation is reduced compared to RRMS
  • There is a more prominent loss of neurons in PPMS

Natural history

At the University of Calgary in Canada, researchers investigated the natural history of 500 people with PPMS. They found that that the median time to reach a high disability score, characterized by the need to use a walking aid, was 9 years. According to their results, older age at disease onset was the most important predictor of disability accumulation in PPMS.

Bilateral motor onset symptoms, which suggest an early spinal cord involvement, were associated with quicker disease progression. In contrast to RRMS, they found no evidence for distinct phases of disability accumulation in PPMS. Disability accumulation in PPMS appears to be affected by the same factors throughout its course.

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