Multiple Sclerosis or MS is an inflammatory, auto-immune condition that impacts the peripheral nerves and the central nervous system. There is no clarity on what causes MS, but studies associate it with the Epstein Barr virus, insufficient vitamin D, environmental factors, or parasites as causes. 

The most common types of MS are mentioned below:

1. Clinically isolated syndrome (CIS)
CIS is the kind of MS wherein one continuously experiences neurological symptoms as a single episode, which lasts for a day or more. These symptoms cannot be tied to infection, fever, or any other sickness. They are an outcome of demyelination or inflammation in the central nervous system. In this MS type, the patient may experience a monofocal episode (single symptom) or multifocal episode (several signs). 

Those with CIS may never experience any other episode. Or this first episode can be an indication of their first MS attack. 

Brain lesions seen in an MRI similar to those present in people with MS indicate a 60%-80% possibility of experiencing another episode. This can be followed by the diagnosis of MS after a few years. One can also get diagnosed with MS sooner if the MRI detects older lesions in a different part of the central nervous system. This is because the older lesions imply that the patient has had an episode in the past, but they were not aware of it. 

2. Relapsing-remitting MS (RRMS)
It is the most common kind of MS. A study by the National Multiple Sclerosis Society suggests that around 85% of people with multiple sclerosis are diagnosed with this type. When one has RRMS, they may experience defined flare-ups or relapses, which results in episodes that deteriorate neurological function. Generally, patients may experience complete or partial recovery periods or remission after a relapse and in-between the attacks. The condition does not progress between relapses. Relapsing-remitting MS includes mild to severe symptoms, and the remission and relapses will usually last for days or months.

3. Secondary-progressive MS (SPMS)
In this form of MS, symptoms aggravate gradually over time. This can happen with or without remissions and relapses, but one’s condition will decline in between relapsing-remitting cycles. If one has RRMS, SPMS can be considered the next stage of the disease. Reports suggest that approximately half of those with RRMS progress to SPMS in about a decade without appropriate treatment.

4. Primary-progressive MS (PPMS)
This is a less prevalent type of MS, and only about 10%-15% of those with MS have PPMS. In PPMS, the neurological function is hampered, and it declines further with the disease. One might experience minor improvements in symptoms, and no relapses occur.