There are several different sorts of pain, in the old days we used to classify pain really according to the timescale and we'd talk about acute pain, meaning pain of a fairly sudden onset that didn't last long. For example, you fall over and bang your knee, it hurts for a while and then it all gets better or you have an operation, say, you have your appendix out and you have that acute pain of the inflammation of your appendix, the acute pain of having had the operation and then the whole thing settles down and goes back to normal.
And we talked about more chronic pains like back pain or the pain, say, of post-herpetic neuralgia, the neuralgia that people get after shingles that can go on for months and years. Nowadays we tend to think of pain more in terms of what was the mechanism that caused it and one of the most important differences is where you have something like a tissue injury, for example the damaged knee when you fall over and bang your knee, you injure your knee, your knee hurts and the nerves pick that up and relay it back to the nervous system.
The pain I mentioned from the shingles and the post-herpetic neuralgia, the nervous system itself is actually damaged there. Shingles is caused by the chicken pox virus and the virus actually attacks the nerves around the spine and damages those nerves, so these are abnormal nerves transmitting unpleasant signals even though in fact nothing may be happening at the far end of that nerve.
The problem lies within the nervous system itself and we call that a neuropathic pain. And there are several other examples of this trigeminal neuralgia in the face, sciatica where people get pain down their leg from a disc, all these are pains where the nerve itself is the origin of the pain and they need different treatments from these pains where for example, if you damaged your knee and it's all inflamed you might need an inflammatory, an anti-inflammatory painkiller or an ordinary sort of painkiller like paracetamol or something a bit stronger like morphine but these drugs aren't so good for neuropathic pains and in fact we use completely different sorts of drugs that work more on the nervous system such as the tricyclic anti-depressants like amitriptyline and the anti-convulsants like gabapentin.
Inflammatory pain for example, rheumatoid arthritis may be different again and we know that in many painful arthritic conditions the nerves in the joint actually change and nerves that normally are silent can wake up so-called silent nociceptors and these nerve endings become extremely sensitive and they have a very low threshold. That means they respond to the slightest thing by giving you pain and it may be this change within the nerves in the joint that actually make conditions like rheumatoid arthritis so painful rather than the actual joint damage itself.
So there are many different sorts of pain and they may need different sorts of treatment and I think that as we learn more about pain and further research is done, we'll probably find that there are other sorts of pain as well and we also know clinically that people often have mixed pain syndromes and that their pain may have some elements of the normal, what we call nociceptive type of pain and other elements may be neuropathic. So it's a complicated business. |
