Definition

• Multiple sclerosis (MS) is a chronic, progressive, immune-mediated disorder of the CNS, initially characterized by inflammatory demyelination followed later in its course by neurodegeneration.
• Although the disorder is presumed to be autoimmune in nature, the antigen(s) driving the immune response remains unknown.

Classification

• Types of MS
  • Relapsing-remitting MS (RRMS): Episodic neurologic dysfunction followed by a complete or partial recovery in between episodes. Most patients are initially diagnosed with RRMS.
  • Primary progressive MS (PPMS): Progressive neurologic dysfunction from onset without relapses or remissions. Less common.
  • Secondary progressive MS: Progressive neurologic dysfunction but follows an initial relapsing-remitting course.
• Classification is important in that progressive forms of the disease, in general, do not respond to many of the first-line disease-modifying therapies (DMTs) effective in RRMS (e.g., interferon-β) but do respond to other therapies (e.g., ocrelizumab in PPMS).

Epidemiology

• Approximately 500,000 patients carry a diagnosis of MS in the US.
• The worldwide prevalence is estimated at over 2.3 million and growing.

Etiology

The exact etiology of MS remains unknown. The pathophysiologic pattern of MS is characterized by inflammatory cell infiltration, demyelination, axonal damage, and gliosis culminating in neurodegeneration.