There are four different categories of MS: Clinically isolated syndrome (CIS): A diagnosis of CIS is made when an individual experiences an episode of neurological symptoms for the first time that is caused by a CNS lesion typical of MS. CIS can be the presenting episode of MS. A diagnosis of MS is made when there is evidence of multiple inflammatory episodes in the CNS over time. Relapsing-remitting: A form of MS that is marked by recurrent episodes of neurological symptoms caused by active inflammation in the CNS (relapses), followed by full or partial recovery (remissions). Symptoms secondary to a relapse typically last weeks or months. Most MS patients initially have a relapsing-remitting course and are diagnosed in their 20s-30s. Primary progressive (PPMS): A form of MS that is characterized by steadily worsening neurologic disability, without any previous clinical relapses and remissions. PPMS patients typically receive a diagnosis in their 40s-50s. Secondary progressive (SPMS): The phase of MS that follows the relapsing-remitting course in some patients. SPMS is characterized by steadily worsening neurological disability in the absence of clinical relapses, and it typically begins after 15-20 years of relapsing-remitting disease. Read more about Dr. Segal's innovative work that is creating new hope for neurological disorders