The different types of MS are categorized according to the course of the disease. At least four distinct patterns or types have been identified: Relapsing-remitting MS (RR-MS) This is the most common form of MS and is characterized by clearly defined exacerbations/relapses (acute attacks) followed by partial or complete recovery. There is no disease progression between the relapse periods. Initially (at the time of diagnosis) RR-MS represents about 85% of all newly diagnosed patients. The definition of relapse requires the new symptom or sign to be present for at least 24 hours, to not be associated with a fever or intercurrent illness (such as the "flu" or a urinary tract infection), as elevated body temperature can unmask silent or old lesions.
Primary progressive (PP-MS) In this form the disease progression is continuous from the beginning without clear relapses. There can be plateaus ( periods of stabilization ). 10-15% of all MS patients are in this group and it tends to occur in older aged individuals. The female to male ratio is equal in this group, unlike other forms where females predominant by about 2:1. Also PP-MS tends to present with fewer cerebral MRI changes and more myelopathy/spinal cord related changes.
Secondary progressive form (SP-MS) This form starts as a RR-MS and later steady progression occurs with or without relapses. Approximately 50% of relapsing-remitting patients progress to the secondary progressive form.
Progressive Relapsing form (PR-MS) This uncommon form (about 5%) is progressive from the onset with superimposed relapses (with or without recovery).
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