Whereas RRMS is marked by periods of remission — times when disease symptoms become less severe — in SPMS, a person’s symptoms steadily worsen over time. There still may be symptom relapses, but changes in symptom severity are generally less drastic than in the RRMS stage and symptoms do not disappear even in the remission phases.
SPMS can be classified as active or not active, based on whether the individual experiences disease relapses or has evidence of new brain lesions. It also can be classified as with or without progression, based on patterns of disability accumulation over time.
Transitioning from RRMS to SPMS
Nearly all people with RRMS eventually will develop SPMS. However, because of advancements in disease-modifying treatments, fewer people today develop SPMS than before, and the transition to SPMS occurs later. The median time to progression to SPMS from RRMS is about 20 years.
Exactly what causes the progression from RRMS to SPMS isn’t completely understood, and there is no single test that defines when MS changes from RRMS to SPMS. A diagnosis of SPMS typically is made after carefully reviewing the progression of the disease in the preceding months and years. Often, six to 12 months of progression must be noted before a person is considered to have progressed to SPMS.
Whereas RRMS symptoms are thought to be driven by active inflammation, SPMS is driven by neurodegeneration, meaning nerve damage that worsens over time. Imaging of the brain generally reveals more new and/or inflammatory lesions in the brains of people with RRMS, relative to those with SPMS.
Last updated: July 8, 2021
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