Multiple sclerosis (MS) is a condition that happens when the immune system attacks the brain and spinal cord.MS can present in a variety of ways including:

clinically isolated syndrome (CIS): describes an episode of neurologic symptoms that are the first clinical sign of possible MS;
relapsing remitting (RRMS): the most common form of MS characterized by intermittent attacks of symptoms (relapses), followed by a short or long period of no clinical attacks (remissions);
secondary progressive (SPMS): after living with RRMS for a long period of time, relapses decrease and symptoms continue progressively without relapses or remissions; and  
primary progressive (PPMS): starting from the initial symptoms, the disease gradually progresses and gets worse without any clear relapses or remissions.