To describe the natural history of a condition or disease. To describe the natural history of a condition or disease. To determine effectiveness or cost effectiveness of treatments/services and/or health care products. To measure or monitor safety and harm. To measure quality of care.
According to the NMSS, attacks or flare-ups of symptoms only qualify as exacerbations if: 1  they occur at least 30 days from an earlier flare-up. 2  symptoms last for 24 hours or longer.
In some cases, there is no recovery from these flare-ups, although in other cases there is recovery. The difference between progressive-relapsing MS and relapsing-remitting MS is that in the former type, the periods between relapses involve continuing progression of the disease.