Clinically Isolated Syndrome (CIS)
A first episode of neurologic symptoms caused by inflammation and myelin damage (demyelination) in the central nervous system (CNS). The episode, which by definition must last for at least 24 hours, is characteristic of MS but does not yet fulfill the criteria for a diagnosis of the disease as CIS may or not become Multiple Sclerosis.
If CIS is coupled with lesions on the brain similar to those seen in MS, as shown by magnetic resonance imaging (MIR), there is a high risk to have a second episode of neurologic symptoms and diagnosis of relapsing-remitting MS.
Relapsing-Remitting MS (RRMS)
The most common form of the disease —with approximately 85% of cases— is characterized by clearly defined attacks or episodes of new or increasing neurologic symptoms (relapses or exacerbations) that may last for several days or weeks. The type and number of symptoms occurring during a relapse and the frequency of relapses may vary depending on the person. Symptoms then ease or disappear (remit). During these periods of partial or complete recovery (remissions), there is no apparent progression of the disease.
This relapsing-remitting pattern may drag on for several years. At the beginning, full —or nearly full— recovery tends to occur after each relapse. Over time, often after 5-15 years, some Multiple Sclerosis symptoms become permanent due to the accumulation of scar tissue in the brain and to the gradual nerve damage.
Primary Progressive MS (PPMS)
A disease course- affecting about 15% of people with MS- characterized by a gradual worsening from the onset of symptoms in the absence of early exacerbations or remissions.
Secondary Progressive MS (SPMS)
Disease form following an initial RRMS course in which there is a steady worsening of the MS symptoms, with or without occasional relapses. Approximately two thirds of people with RRMS will develop SPMS after 15 years.
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