Peripheral nerve injuries
Peripheral nerves put up with a lot, but sometimes things do go wrong. To find out how peripheral nerves can be damaged, Katie Haylor spoke with consultant neurologist and researcher Rhys Roberts from Cambridge University and Addenbrooke's Hospital...
Rhys - Diseases of the peripheral nervous system are generally called peripheral neuropathies. There are various estimates but roughly around 2 percent of people will have a peripheral neuropathy at any one time and some estimate that as we get older it can go up to around 8 percent of the population. Now peripheral neuropathies themselves, the problems can be split into two main types. So there are conditions that you have inherited, these are genetic conditions many of which as we now are able to sequence DNA much easier than previously, we’re able to pinpoint specific changes that lead to diseases of the peripheral nervous system, but also a very large group which are what we call acquired so these are factors which have come in from outside.
So within the acquired part there's a very very very long list of other conditions that can lead to peripheral neuropathies and these can be other medical conditions or they can be certain things that have affected the nervous system, either being exposed to an agent or a medication that has been used for another condition which has had an effect on the nerves.
By far the commonest cause of peripheral neuropathy that we see is due to secondary related diabetes. So roughly two thirds of people with both Type 1 diabetes and Type 2 diabetes which you've heard of will have a neuropathy. So this is very common and if you think how common diabetes is, and the commoner it gets with time this is a significant problem. Clearly to what extent people living with diabetes will be affected obviously varies from person to person, and also how well controlled the underlying condition is. Of course people with diabetes can often have an affected autonomic nervous system as well which can have an effect on their blood pressure and their ability to sweat and also on their gastrointestinal system.
Katie - So why would diabetes cause nerve issues? Because you do hear about people having tingly feet or tingly fingers, why is this the case?
Rhys - That's a very good question. We don’t quite understand why diabetes affects the nerves. What we do know is that the nerves are supplied by very small blood vessels. And plays a very important part in the function of the peripheral nerves. We know in diabetes that the blood vessels can be affected and there's certainly a higher risk of cardiovascular disease so it is likely there’s going to be a combination between the high sugar, the dysregulation in fats, and also the effect on the smaller blood supply certainly to the longest nerves.
There’s trauma. So when people have injuries and so forth that can sever the axon of the peripheral nervous system meaning that the signals can’t get across that injury and anything downstream of that site will either be weak or you’ll be numb.
Katie - So this is a physical trauma that essentially snips apart, almost like a pair of scissors, the nerve and it becomes disconnected?
Rhys - Correct and whilst the nervous system and the Schwann cells in particular will react to these injuries in an attempt to guide the growing axon back to where it was before, this not only can take a long time but on occasions the axons won’t get back to exactly where they were previously.
Katie - So can that result in paralysis then?
Rhys - Yes yes. So any structure that was innovated then by these nerves essentially the signals wouldn’t be getting to for example the muscles. So you’d be weak, the muscles will get smaller. Leading to the inability to move or perform a function, and likewise any signals that came back by that nerve to the spinal cord to convey any sensation and so forth and that would be impaired as well.