As far as symptoms, RRMS and PPMS are oftentimes very different from each other.

People with RRMS enter periods of flare-ups and remission, while those with PPMS are in a continual phase of deterioration.

However, recent research has shown through MRI scans that certain characteristics — such as the amount of demyelination — overlap. More research is still needed to see if there are other links between RRMS and PPMS.

RRMS is the most common form of MS. It affects as many as 85 percent at initial diagnosis. RRMS is characterized by flare-ups or attacks of inflammation in the central nervous system.

These flare-ups are followed by remission periods with improved or completely resolved symptoms. People who’ve been living with RRMS for 10 years gradually develop SPMS.

RRMS symptoms come on suddenly and include episodes of:

There are several disease-modifying therapies available to treat RRMS. Many of these can also be used to treat progressive forms of MS in those that experience relapses.

PPMS is characterized by a steady worsening of neurologic function without distinct attacks or remission periods.

This type of MS involves considerably less of the type of inflammation seen in RRMS, resulting in fewer brain lesions and more spinal cord lesions.

There’s currently only one medication — ocrelizumab (Ocrevus) — approved by the FDA for treating PPMS. However, disease-modifying medications used to treat other forms of MS may help reduce inflammation in the central nervous system. This is where nerve degeneration occurs for those with PPMS.

New research and clinical trials are ongoing to find more treatments specifically for PPMS.

The following are some of the key differences between RRMS and PPMS:

In general, PPMS tends to be more debilitating than RRMS.

Those with PPMS may therefore also find it more difficult to continue working because of their impaired mobility and declining neurologic function.