Multiple Sclerosis

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system. Inflammation damages myelin and, importantly, the underlying axons. Loss of myelin slows or blocks saltatory conduction, so a lesion can produce optic neuritis, limb weakness or numbness, diplopia, ataxia, bladder dysfunction, or other focal neurological deficits depending on its location. Inflammatory activity is episodic in many patients. Relapsing-remitting MS is the most common phenotype at onset; attacks are followed by partial or complete recovery, although repeated injury may leave permanent disability. Some patients later develop secondary progressive MS, in which disability gradually accumulates. Progression may be active, with recent relapses or new MRI lesions, or non-active. Primary progressive MS follows a gradual worsening course from the beginning rather than distinct attacks. This distinction matters therapeutically. Disease-modifying therapies (DMTs) suppress or alter inflammatory immune activity and reduce relapses, new MRI lesions, and future disability accrual. They do not rebuild axons already lost or reverse established neurological damage. A patient may therefore have stable MRI activity but persistent weakness, spasticity, neuropathic pain, fatigue, or impaired balance from prior injury.