​Definition: An acquired, chronic, immune-mediated, inflammatory condition of the central nervous system (CNS) that can affect the brain, brain stem and spinal cord. The inflammatory process causes areas of demyelination (damage to white matter), gliosis (subsequent scarring), and secondary neuronal damage (cell loss) throughout the CNS. Typically, MS first develops in young adults and can include a wide variety of neurological symptoms and signs: Multiple sclerosis (CKS), Multiple sclerosis (NHS Choices), Multiple sclerosis (Mayo clinic), MS Society

3 main patterns:

1. Relapsing–remitting MS (RRMS): episodes or exacerbations of symptoms (relapses) are followed by recovery (remissions) and periods of stability. In the early stages of RRMS, symptoms may go completely during remissions. However, typically, after several relapses there remains residual damage to parts of the CNS which results in only a partial recovery during remissions. About 85% people with MS have RRMS at onset.

2. Secondary progressive MS (SPMS): the onset of MS is of the RRMS pattern. But, at some point later, the disease course changes and neurological function gradually worsens, with or without continued relapses. About 25% of people with RRMS progress to SPMS within six years of disease onset, and about 50% by 15 years of disease onset.

3. Primary progressive MS (PPMS): there is a steady progression and worsening of the disease from the onset, without remissions. Occurs in about 10–15% of people with MS

Diagnosis is complex and should be made by a specialist. No single investigation is diagnostic (CSF oligoclonal IgG bands, demyelination on MRI, NCS, visual evoked potential delays...)

New CNS symptoms defining an MS relapse need to last >24 hrs after a stable period of at least 1 month