The main difference between secondary-progressive MS (SPMS) and primary-progressive MS (PPMS) centers on the presence or absence of relapses. SPMS develops in patients who initially had relapsing-remitting MS (RRMS) as a secondary phase of that disease course. By contrast, PPMS follows a progressive disease course from the beginning in patients who never experience relapses.
Who develops SPMS?
SPMS is a form of MS which follows RRMS, the most common form of MS affecting 85% of patients diagnosed with MS. Most patients with RRMS will eventually develop SPMS. Their MS will become more steadily progressive, with increasing disability and loss of neurologic function, while they experience fewer and fewer relapses.
How is SPMS different from RRMS?
When RRMS transitions into SPMS, the disease becomes more progressive with a gradual worsening of symptoms or loss of neurologic function. With RRMS, flare-ups or exacerbations are usually followed by periods of remission, during which time symptoms improve somewhat or completely.
In contrast to RRMS, where symptoms during attacks are primarily caused by inflammation, in SPMS, symptoms are caused by the permanent damage or loss of nerves and/or brain atrophy. With SPMS, the patient may continue to have relapses (exacerbations, flare-ups, or attacks) with slight remissions and plateaus, while experiencing a general worsening of symptoms and neurologic function.
When does the transition to SPMS happen?
Before disease-modifying treatments became available, research found that about half of patients who were initially diagnosed with RRMS would develop SPMS within 10 years and 90% would develop SPMS within 25 years.
It is believed that MS medications may be able to slow the progression of MS, however we do not currently know how effective disease-modifying treatments are in delaying the transition of RRMS to SPMS.
How is SPMS diagnosed?
It is difficult to know exactly when RRMS has transitioned to SPMS because this transformation can happen very gradually. However, there are clues that the transition to SPMS has taken place.
If MS symptoms continue to worsen after an exacerbation has ended, this may mean that the patient has transitioned from RRMS to SPMS. However, if increased symptoms persist but stabilize following an exacerbation, then the patient may still be considered to have RRMS.
Tools to help determine if a patient has transitioned from RRMS to SPMS include a careful medical history and neurologic exam, during which the doctor notes changes in a patient’s symptoms. Laboratory tests including repeat magnetic resonance imaging (MRI) may also be useful in detecting disease progression.