How It Manifests:
The “cable” of the nerve that connects one nerve cell with another, the axon, is coated with a substance made of protein and fat called myelin. This enhances the conduction of electricity down the axon. MS produces injury in the central nervous system when the immune system mistakenly attacks myelin. Areas of myelin damage are known as plaques, or lesions, and these eventually fill in with scar tissue.
The name multiple sclerosis means “many scars.” MS can also cause destruction of the entire nerve. The damage from lesions disrupts the transmission of nerve impulses from the central nervous system to the rest of the body causing a variety of symptoms.
“Types” of MS
In the past, MS was commonly divided into four separate forms or “types” of the disease. Today we think of MS as one distinct disease, with different symptoms from person to person, but also changing manifestations over the course of the lifetime of a single patient. There is still debate as to how distinct or different these forms of MS are from each other, but it’s nonetheless useful to look at these four categories as a way to explain how MS manifests at different stages in different people.
Clinically Isolated Syndrome and Radiologically Isolated Syndrom (CIS and RIS) both describe the very earliest detectable signs of MS. CIS is when the first outward, clinical signs of the disease, or the first relapse. We say “isolated,” because by definition CIS is observed without ongoing symptoms or continued relapses. Commonly this is between the ages of 20 to 45, but may be younger or older. Typical symptoms might be numbness, or visual disturbance such as optic neuritis. An individual after this first attack may already fulfill formal criteria for a diagnosis of MS based on the symptoms and lab tests, but if not, we simply call it a CIS. RIS is when MS lesions are observed on an MRI scan, but no outward symptoms or signs of relapse are present.
Over time, if a patient has more clinical symptoms, and/or new changes on MRI scans, they would then fulfill formal diagnostic criteria for MS. If a person never experiences another exacerbation, or their MS does not progress or get worse over time, this singular event is said to be CIS. Most patients however will eventually experience another exacerbation, in which case they fulfill criteria for a formal diagnosis of MS.
Relapsing-Remitting MS (RRMS) is diagnosed in someone when they have a second attack and/or new changes on MRIs over time. Typically, these would affect different parts of the CNS, and then an individual would formally fulfill criteria for MS. Up to 85% of people diagnosed with MS have relapses when diagnosed. For most with RRMS, relapses and new MRI changes are most common when they are younger, and risk of new relapses diminishes with age.
Secondary Progressive MS (SPMS) manifests about 10-15 years, on average, after a diagnosis of RRMS. Some (but not all) will begin to more overtly show signs of slowly worsening symptoms unrelated to, or in addition to, relapses. This may be manifested especially with greater walking and cognitive problems, and is called SPMS. Men, and especially those with very active relapses when first diagnosed, are at higher risk of developing SPMS. We now recognize that CIS, RRMS, and SPMS are all “relapsing” forms of MS. This is relevant to treatment, as younger patients with active disease with recent relapses or new scan changes are more likely to benefit from present MS meds, regardless of whether this is called RRMS or SPMS.
Primary Progressive MS (PPMS) is diagnosed when someone has a steady progression of MS symptoms that is not preceded by relapses. Average age of onset is similar to those with SPMS, about 40-45. Followed long enough, a minority of those with PPMS could have a relapse.
