Secondary progressive MS occurs in around 65% of those with initial relapsing-remitting MS, who eventually have progressive neurologic decline between acute attacks without any definite periods of remission.
Sekundær progressiv MS beskriver omkring 65 % af de, der indledningsvist har haft relapserende-remitterende MS, men som begynder at have progressive neurologiske problemer mellem akutte angreb uden nogen egentlig periode med remission.