The study looked at people with relapsing onset multiple sclerosis (R-MS) to see how many transitioned to secondary progressive MS (SPMS) and how disability progressed in SPMS. They found that older age at MS onset, being male, and having residual disability after onset increased the likelihood of developing SPMS. For those with SPMS, being male and having higher disability levels at onset increased the risk of reaching disability milestones, while older age at SPMS onset lowered the risk of progression. These findings can help plan services and guide future treatments for SPMS.