Multiple sclerosis (MS) is a neurodegenerative disorder that damages the nerves in the brain and spinal cord, leading to problems with muscle movement, balance, and vision. MS is an example of a demyelinating disease, where myelin, which is the protective coating that surrounds nerve fibers, becomes damaged.
Image Credit: Lightspring / Shutterstock.com
Multiple sclerosis follows a different course in every individual; however, there are three primary ways in which the disease can progress, depending on which form of the illness a patient has.
It is estimated that up to 80% of all individuals with MS have the relapsing-remitting form of the disease. These individuals have periods where their symptoms are mild or absent, which is otherwise referred to as remission, followed by periods of symptom relapse. Symptoms may occur suddenly and in acute bouts or exacerbations. During periods of relapse, symptoms may become worse each time.
The relapsing-remitting form of MS may eventually progress to secondary progressive MS (SPMS), during which there are few or no periods of remission. Relapsing-remitting multiple sclerosis (RRMS) can be diagnosed when two episodes of relapse are separated by more than 30 days, or there has only been one relapse that is accompanied by MRI evidence of newly scarred or damaged myelin three months later.
Understanding Multiple Sclerosis: Types of MS
Patients with SPMS often experience phases of relapse followed by remission at first. However, as SPMS progresses, it may eventually lead to the progressive form of the disease, which is characterized by worsening symptoms and few or no periods of remission.
The least common form of multiple sclerosis is primary progressive MS (PPMS), which occurs in about 10% to 15% of all cases and usually in people over the age of 40. In this form of MS, symptoms worsen over time rather than occurring in bouts or as sudden attacks.
PPMS may be diagnosed if there have been no previous symptoms of relapse but the patient has become increasingly disabled over a period of at least one year.