Around 85% of people with multiple sclerosis (MS) are diagnosed first with the relapsing-remitting form of the disease (RRMS).
Relapse is defined by the appearance of new symptoms or the return of old symptoms for 24 hours or more, without a change in the body temperature or infection. In RRMS, patients experience inflammatory attacks on nerve fibers and the myelin sheaths that protect them. During attacks, newly damaged areas appear and lead to some more common MS symptoms. Symptoms may vary among people with MS because the affected areas are different.
During remissions, all of the symptoms may disappear or some may continue and become permanent. However, no apparent progression of the disease occurs during this time.
Relapsing-remitting multiple sclerosis can be characterized as active (with relapses or evidence of new activity seen on an MRI) or not active, and worsening or not worsening. In other words, there may be or not be an increase in disability over a specific period of time following the relapse.
RRMS differs from progressive types of MS because in RRMS the relapses represent new inflammatory attacks on the central nervous system (CNS). Much less inflammation is present in the progressive forms of the disease.
People with RRMS usually have more brain lesions with more inflammatory cells. People with progressive types of MS experience more spinal cord lesions with fewer inflammatory cells.