Relapses are triggered by white blood cells
entering the brain and damaging the oligodendrocyte (0) and nerves (N). This coupled with swelling of the nerve, serves to stop the nerve impulses firing properly. This leads to symptoms.
Current effective treatments work by stopping the white blood cells entering the brain. In my current opinion these will not work to stop the underlying cause of progressive MS.
We know this because of the many failures of trying to treat progressive MS.
Some Doctors however continue to believe that progessive MS is a problem of white blood cells and carry on regardless. Indeed some Progressive MSers will probably respond to these drugs, particularly those with gadolinium enhancing lesions. However, we need a new approach to treat progressive MS, because the main problem appears to not be with the white blood cells (although I think that these need to be dealt with also) but appears to be a problem with the nerves, that has been triggered by the damage caused by white blood cells.
Nerves transmit nerve impulses
(see videos in British
English to Explain) from one nerve to another across a synapse
). Transmission of the nerve impulse uses energy to transmit the impulse, which results from movement of ions largely sodium
(Na) and potassium
. (K) Sodium enters the cell by sodium channels (pores that allow sodium to flow through them) in the nerve. Once the impulse passes the nerve resets itself so that it can transmit the next signal. Within the nerve there is a exchanger
(imagine a revolving door). The system pumps calcium
(Ca) out of the cell in exchange for sodium. This all helps maintains the health of the cell and te balance of sodium within the cell The myelin
sheath made by oligodendrocytes allows the nerve impulse to travel faster. This is because the nerve impulse jumps acrossto the gaps (Nodes of Ranvier
) between individual myelin sheaths. (There are lots of videos/tutorials on youtube those by khanacademy.org
are informative. (If you watch these- a schwannn celll myelinates peripheral nerves and those in the brain are myelinated by oligodendrocytes but otherwise the message applies to the brain)
In progressive MS (both primary and secondary), loss of myelin is a feature of the disease. Initially this damage may be repaired. But as we get older our repair mechanisms become less effective. Furthermore the disease may kill too many of the repairing-cells and the scarring from the damage may stop repair. This makes the nerves vulnerable to further damage.
Why one person gets relapsing MS verses Progressive MS is not clear at the moment. It may depend on age, sex, where the attack occurs within the nervous system and how well an individual can repair and deal with the consequences of damage. As the compensation mechanisms become exhausted or are not there in the first place (from PP MSers) damage from progressive MS takes over from damage caused during relapsing MS.
Once nerves are demyelinated, to keep the nerve impulses moving the nerve must use alot more energy. Low level inflammation which is present in all MS types such as that produced by microglial
cells produces mediators such as nitric oxide
that stop cells from making enough energy. This blocks the action of the energy-dependent sodium-potassium
pump. This results in excess sodium entering the nerve, via the sodium channels
. This excess sodium in the cell can cause the sodium-calcium exchanger to go into reverse and it pushes sodium out of the cell whilst pulling calcium into the cell. This can be bad news as too much calcium in cells triggers them to commit suicide
. Therefore simple electrical activity of the nerves can be a problem for demyelinated nerves. As nerve circuits are damaged and lost the brain compensates by using different circuits to perform the task. As nerves are lost it puts more of a strain on the remaining nerves, leading to further nerve loss and the accumulation of progressive disability.
With this scenario progressive disease can occur in the absence of white blood cells and explains why current MS drugs are not useful for progressive MSers. Importantly it gives us clues on how to treat MS. One obvious route is to repair the myelin, but others such as blocking the accumulation of toxic concentrations of ions in the nerve are even more feasible, because these types of drugs are already availble to treat other diseases such as epilepsy. The guess work is which ones or combination are more likely to succeed.
This however is just theory and will become more concrete when treatments based on this theory are shown to be active. Until then we keep an open mind to alterative ideas.
This is currently being investigated in MSers to provide the evidence base that allows change to occur…and more many studies on this aspect are being planned but as you know this takes time.
Too technical? See Part I and the rest of the series.