Optic neuritis and MS: a window into the brain
The epilepsy bitGrowing evidence shows a build-up of sodium ions in the brain may contribute to nerve damage in the central nervous system (CNS). Phenytoin, an epilepsy treatment, works by blocking sodium channels – the proteins responsible for letting sodium ions in and out of cells. The theory behind this research is that if sodium ions do contribute to nerve cell damage in MS, then blocking their entry to nerve cells could be protective.
The optic neuritis bit
Optic neuritis occurs when the nerve that transmits information from the eye to the brain (the optic nerve) becomes inflamed. It’s a condition in its own right but it’s also experienced by some people with MS. It can cause sudden blurred vision and partial or even total blindness.
The visual system provides a window into the brain, making it really useful for understanding nerves. The optic nerve and retinal nerve fibre layer (the layer of nerves between the optic nerve and the retina) are easy to image non-intrusively so that we can observe changes which could indicate damage.
The MS bit!
The important part of all this for MS is that any changes observed in the retinal nerve fibre layer as a result of administering a treatment may also be translatable to the rest of the CNS, and therefore could be beneficial in MS. In short, if drugs are found to be protecting nerves in optic neuritis then they could have a similar effect in MS which is really exciting!
The study in question
In this phase 2 study, 86 people experiencing early symptoms of acute optic neuritis were given either phenytoin or a placebo drug for three months. The researchers then assessed whether the drug could help to protect the retina (the light sensitive nerve layer at the back of the eye) from damage by measuring the thickness of the retinal nerve fibre layer, once at the beginning of the study, and again six months later.
The researchers found that phenytoin caused:
- A 30% reduction in the loss of retinal nerve fibre layer compared to placebo.
- A 34% reduction in loss of macular volume (the most light sensitive part of the retina) compared to placebo.
- A 38% reduction in optic nerve cross sectional area compared to placebo
The crux of it all
This study supports the concept of neuroprotection - protecting nerves to keep them alive.
This is a vital strategy for the future of MS treatment and currently there aren’t any drugs available that can protect nerves from damage. Finding these results using phenytoin which is already licensed for use in epilepsy has cost and safety benefits, as well as enabling faster translation of therapies to people with MS.
This study should encourage a phase 3 trial of phenytoin in optic neuritis and other demyelinating conditions such as MS, paving the way for the development of a neuroprotective drug for people with MS.