Multiple sclerosis, an autoimmune disease that attacks the central nervous system, can be split into two main trajectories: primary progressive MS and relapsing-remitting MS. While people with either type of MS may experience similar MS symptoms, the condition follows a different course in each.
“Primary progressive MS is a slow thing that happens over months to years,” says Michelle Fabian, MD, a neurologist at The Mount Sinai Hospital in New York City. “It’s more of a gradual symptom, and then it doesn’t typically go away.”
Affecting just 15 percent of MS patients, primary progressive MS is significantly less common than relapsing-remitting. The average age of onset is between 35 and 39, according to John Hopkins Medicine, which is older than the average age of diagnosis for MS overall.
Both types of MS occur when the immune system turns against itself. This part of the body is supposed to protect the body from dangerous pathogens, but instead, the immune system of someone with MS begins attacking crucial parts of the central nervous system: the brain, the spinal cord, and optic nerve, which connects the brain to the eyes.
Patients with relapsing-remitting MS alternate between relapses, or periods when new symptoms emerge or worsen, and remission, when symptoms subside.
With primary progressive MS, patients don’t experience relapses. “It comes on slowly, and it’s usually a walking challenge that happens over months and years,” says Dr. Fabian. With difficulty walking comes other challenges, such as fulfilling job responsibilities or everyday activities.
In MRIs, patients with either form of MS tend to show nearly identical results. Those with primary progressive MS sometimes have more lesions in their spinal cord than their brain, according to Dr. Fabian, but not necessarily. (Learn how multiple sclerosis affects the body here.)
Because test results cannot always distinguish between the two forms, talking to the patient is often the most revealing way to detect primary progressive MS. “Five years ago, they might have had just a touch of a trouble walking,” says Dr. Fabian. “Two years ago, it was more, and now it’s more. It’s a very different story.”
Treating primary progressive MS has posed more of a challenge than relapsing-remitting. A new treatment has recently been approved that can treat both forms of MS and will hopefully begin to change the outlook for the men and women diagnosed with primary progressive MS.