Evoked potentials (EPs) is a technique that allows us to test the electrical conduction in a particular pathway within the nervous system. If the conduction is slow it tells us the particular pathway being tested is demyelinated.
EPs can be very helpful in making a diagnosis of MS; EPs can be used to show sub-clinical or asymptomatic involvement of a particular pathway.
Aim: This study assessed combined EPs as a marker and predictor of the disease course of early MS over 3 years.
Methods: 50 MS’ers in the early phase of RRMS prospectively underwent visual, sensory and motor EPs and disability (EDSS) assessments at baseline and at 6months intervals for 3years.
Results: EDSS correlated with the sum of the EPs. The change in the sum of the EPs correlated with the change of EDSS
Conclusions: EPs correlate well with clinical disability in cross-sectional and longitudinal comparison in early MS and allow prediction of disease evolution over a period of 3 years.
Epub ahead of print: Schlaeger et al. Combined evoked potentials as markers and predictors of disability in early multiple sclerosis. Clin Neurophysiol. 2011 Jul 19.
“Why is this study important? Firstly, it confirms that EPs can be useful in the diagnosis of MS. More importantly, however, this study shows that EPs may be suitable as a marker of remyelination. If for example you have a delayed visual EP, for example instead of conduction at 100 milliseconds your left optic nerve conducts at 120milliseconds, an effective remyelination therapy would have to reduce this delay.”
“EPs will almost certainly be used to assess remyelination thearpies.”
“Do you know what the clinical effects of delayed conduction speed in an the visual pathway?”
Additional reading: evoked potential
This is interesting. So in effect, it would be worth it for everyone in the process of being diagnosed to have EP tests, even if their symptoms have not included optic neuritis?
Re: "This is interesting. So in effect, it would be worth it for everyone in the process of being diagnosed to have EP tests, even if their symptoms have not included optic neuritis?"It depends on the clinical and MRI evidence; you may have enough evidence to support dissemination in time and space without EPs. However, EPs give you neurophysiological (electrical) evidence to support a diagnosis of demyelination. For PPMS EPs should be done, unless you want to make a mistake!
"EPs will almost certainly be used to assess remyelination therapies."Prof G,But what is the aim of such re-myelination therapies? If the axons are severed, there's nothing to re-myelinate. If there is scarring, I'm guesing the scar will act as a barrier so little point re-myelinting unless the scar can be removed. I'm not sure this has been thought through.On the other hand, Prof Scolding's initial stem cell trial (early results) did indicate some benefit.
Re: "But what is the aim of such re-myelination therapies? If the axons are severed, there's nothing to re-myelinate."That's the point about EPs. The fact that you are able to get an EP tells you that the nerve fibres are intact. It is believed that fibres that conduct slowly, i.e. demyelinated, are vulnerable and destined to die over time. Therefore EPs let you know that you have a vulnerable pathway and that if you achieve in remyelinating it (increasing its conduction speed) you may be protecting it from degenerating in the future. I don't think the scar tissue is an issue here; I would not target a pathway that had no conduction; in a proof-of-concept study that would be a hurdle to high to start with. I would only focus on pathways in which you could elicit an EP with slow conduction.