The inflammation that occurs early in the MS disease process — and is the hallmark of relapsing-remitting (RRMS) — slowly lessens over time. Fewer inflammatory changes occur in the central nervous system and the person experiences fewer relapses. Even though there are few or no relapses at this point in the disease, a gradual worsening of symptoms over time is common; this worsening is known as disease progression. The term “secondary-progressive” comes from the fact that secondary–progressive MS (SPMS) can only be diagnosed in a person who has previously experienced RRMS.
Because the transition from a relapsing-remitting course to a more progressive one is a gradual process, the physician will not be able to tell exactly when it is happening. If a person’s symptoms are worsening, the challenge for the doctor is to determine whether:
The worsening is left over from the last relapse (in other words, permanent but stable damage that remains after the inflammatory attack has ended) — which would mean that the person is experiencing an RRMS disease course; or
The disease is continuing to worsen even though the person is no longer experiencing inflammatory relapses — which would mean that the person has transitioned to a SPMS disease course.
A variety of strategies, including a careful history of the changes in a person’s symptoms, the neurologic examination, and repeat magnetic resonance imaging (MRI) scans, help determine whether the transition to SPMS has occurred.
Read about the diagnosis of SPMS.