Recently we have had several people ask how one knows when you move from RRMS to SPMS. The first thing we must all know is that this is a somewhat subjective assessment that should be made by our neurologist. The second thing you need to know is that it is an assessment made on the basis of the patient's symptoms and disability - not on the basis of the MRI.
Studies show that about 50% of all people with RRMS will progress to SPMS during their lives. If we all lived another 40 years or so, that number might be much higher, as the current thought is that SPMS is the next step in the disease process of Relapsing Remitting MS. One of the main goals in the current use of DMDs is to slow this transition.
There are two main patterns of SPMS. One is that the relapses stop and the symptoms just inexorably continue to worsen causing ever-increasing disability. This is the easier to recognize. The person just gets worse and worse , but now does not have periods of noticeable improvement or stabilization. Very typically, their ability to walk unassisted goes downhill steadily. Neurologists have scales by which they measure disability. The most common that we see is called the EDSS.
In this type, the person with MS can no longer really pinpoint the dates when new things appeared, and they notice that, once a symptom appears, it never seems to go away. There may be brief periods where symptoms stay the same, but over time they just continue to worsen.
The other pattern is one in which there continue to be relapses - where there is a noticeable worsening of old symptoms or appearance of new symptoms. However, between these relapses, they no longer see improvement in the symptoms that are already there. There is a continual increase in the permanent disability - usually defined as the ability to do the activities of life whether that is walk unassisted, dress or bathe unassisted, prepare meals and eat, etc.
The person with this relapsing SPMS will still notice periods where symptoms suddenly appear or worsen, but in between these relapses they notice that other problems are still sliding downhill. As an example, they may now have an onset of severe vertigo, but the old leg weakness slowly worsens so that they need more rests, then a cane, then a wheelchair for longer walks and finally a wheelchair most of the time. Or it may not progress fast, but they notice that it is taking longer and longer to walk from the street into the store, or that they are getting less and less done on each shopping trip. Mainly, now, they see that symptoms never really improve once they have appeared.
What is happening? What can be done?
Researchers feel that the onset of the first kind of Secondary Progressive MS indicates that the process of nerve death is the most prominent thing happening. There isn't so much inflammation causing myelin damage and definitely no myelin repair happening. In this kind of SPMS the firstline DMDs have not shown much help. The docs will begin to consider the second line meds, Tysabri and Novantrone.
In the kind of SPMS that still has a relapsing pattern, though, there still appears to be a component of inflammatory attacks on the myelin. In this second kind of SPMS the neuros will often continue to use a DMD to try to slow the process. However, the relapsing phase of SPMS is typically expected to burn out and turn into the pure progressing phase eventually.
The MRI does show things also, but the transition from RRMS to SPMS is not a determination made by MRI - just bolstered by it. The lesion load may grow more rapidly without resolution of any lesions. Also, T1 black holes may become more prominent or more numerous. Gray matter lesions may multiply and the big finding is visible atrophy of the brain matter, such that you can see that so many neurons have died that the brain is literally shrinking.
The above describe patterns not specific instances.