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We were lucky enough to have a pain managment doc land on our forum. He has offered us some basic information on the nature of nerve or "neuropathic" pain and a discussion of how it is treated.
PAIN - The Musical
There are fundamentally two types of pain in world: "normal pain" and "neuropathic pain." Normal pain happens when someone kicks me in the shins. It turns out that there are separate nerve fibers that create the sensation of pain, and the reason you can feel pain in every part of your body is that every part of your body is covered by a web of pain-creating nerves. Normally this web of of nerves sits there all the time doing nothing. These nerves just sit there quietly. When I get kicked in the shins, those pain-creating nerves come alive and IN RESPONSE TO THIS STIMULUS AND ANY TISSUE DAMAGE they start to fire, sending signals of "hurt" to the brain. The faster they fire the more pain I will feel. This is normal pain. It occurs in response to injury, and is a normal function of a properly functioning nervous system.
In contrast, sometimes an injury occurs (surgery, car accident, fracture etc) that injures the nerves themselves. While many times the injury of a nerve just leads to numbness, in some people it leads to chronic pain. In these cases the injury to the nerve has caused the nerve to put new kinds of proteins on its surface and ultimately changes the firing behavior of these pain-carrying nerves. One of the changes that happens is that the nerves start to fire spontaneously--without any external stimulus (such as the kick to the shins). This means they acquire a "pacemaker effect" (like the heart) they just go on firing all the time regardless of what is actually happening to you. If the nerves doing this are the pain nerves in the front part of your shins, and they are firing away all by themselves because of some long ago trauma, then you will continue to feel pain in the shin area. Your brain intereprets these abnormal signals as if they were normal signals and says "These signals from these nerves in the shin mean I have pain in my shins". The patient in this case continues to feel pain even though the surrounding tisse is not injured and no one is continuing to kick the shins. This pain is THE NERVOUS SYSTEM WORKING ABNORMALLY and is referred to as "neuropathic pain."
Often this pain is described as shooting, electrical or burning--and, in this case, your doctor may well recognize your pain as neuropathic. However, in reality neuropathic pain can be aching, sore, dull, pressure, or sharp as well. Sometimes it is associated with numbness and tingling, but more often it is not. So PAIN QUALITY is not a reliable indicator of whether your pain is neuropathic. Neuropathic pain is someimes associated with two otherwise unusual symptoms: 1) a normally non-painful stimulus (ie brushing aginst the skin over the affected area--clothes or a casual touch) is experienced as causing pain ( the patient says "I cannot stand my pants rubbing the skin over my knee" etc-- (something you don't see if the pain is coming from arthritis in the knee) and 2) a normally painful stimulus (a gentle pinch) is felt as excrutiatingly painful. These two symptoms are called "allodynia" and "hyperalgesia".
The TIMING of pain is often a clue about whether pain is "neuropathic" or "normal". Because neuropathic pain is caused by the pain nerves firing abnormallly irregardless of any stimulus, it is often always there regardless of what the patient is doing. Constant pain every minute of the day, every day is highly suggestive of nerve injury and neuropathic pain. Some unusual nerve pain syndromes (trigeminal and other cranial neuralgias ) cause intermittent explosive type pains, and some nerve impingments are dynamic (eg a nerve root is squeezed in the back when the patient is standing but not when the patient is lying down) in which case the pain can be intermittent but nonetheless is still neuropathic. However muscle pain, joint pain and other kinds of normal pain typically are absent in somepart of the day or in some position.
Because nerve pain happens in the setting of nerve injury, often, if you look closely, you can find other subtle evidence of nerve injury. One easy test is to put an ice cube in a plastic bag and touch the skin in the area of maximal pain--where you would touch if you had to put just one finger at the site of maiximal pain-- and then touch the identical area on the opposite side. If there is nerve injury the painful side will often feel a little less cold -because temperature carrying nerves are like pain nerves and easily injured. This can sometimes be a challenge in patients with nerve pain. The overwhelming strength of the incoming pain signal can overwhelm the spinal cords ability to decide where the pain is coming from and the patient then can difficulty exactly localizing where the pain is coming from. The extreme of this happens with some severe nerve injuries where patients can report "mirroring" of their pain-- ie they start off feeling the pain in one hand or one knee and over time they start feeling it in the opposite hand or knee.
this was written for us by Paindoc38
The nerve pain that we have here on the forum is neuropathic pain from an injury, but the injury in the case of Multiple Sclerosis has happened in the spine or brain. The demyelinating attacks cause the sensory nerves carrying pain signals to the brain to begin firing spontaneously. As we have discussed before, a pain nerve can do two abnormal things after it is injured. It may send no signal at all. In that case the result is numbness at the spot that that nerve originated. Or it may send pain signals inappropriately, resulting in neuropathic pain at the origin site.
Paindoc has also offer to give us an overview of ways to treat and manage nerve pain. This is wonderful, because inadequate relief from pain is one of the greatest problems here. Also, we have been told by our doctors that if a pinful paresthesia is burning, then it has to be from damage from Diabetes. This is not a useful rule.
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