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Old 12-30-2009, 07:39 AM
glenntaj glenntaj is offline
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Join Date: Aug 2006
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glenntaj glenntaj is offline
Magnate
 
Join Date: Aug 2006
Location: Queens, NY
Posts: 2,857
15 yr Member
Default Well--

--all other things being equal, in general, damaged nerves, or nerves undergoing repair from damage, tend to produce more odd sensations (parasthesas) and out of proportion pain (allodynia) than nerves that are dead, which are more likely to result in numbness in the area that is dead.

But--and it's a big but--nerve damage can be very patchy and incomplete. Many have reported having pain and numbness in the same area at the same time, and been mystified (probably for much the same reasons you're mentioning). It's no logical, but if one considers there are a number of different types of afferent fibers--those in myelinated nerves, those in thinly myelinated nerves, and those that are unmyelinated, and that these all have different overall structures, it's possible for one subtype of nerve in an area to be damaged to greater or lesser degree than another (or for them all to be globally damaged). This can get quite specific--there've been reports of people with only cold allodynia, meaning only the nerves that sense cold were damaged, people with only light touch allodynia, etc.

And it's not necessarily unusual to have somewhat different pain sensations at different "skin levels"--or to have pain at one "level" and numbness at another. With all of the weird sensations that damaged nerves result in, it can be very hard, merely by subjective experience of symptoms, to know exactly which nerves are involved. And I haven't even yet mentioned the possibility of "crosstalk"--damaged nerves often release chemicals that inflame their previously undamaged neighbors, and start them firing nastily--reflex sympathetic dystrophy/complex regional pain symdrome is thought to possibly start this way--or of pain signals being referred to points beyond the site of the original damage, which is common, especially in inflammatory or compressive situations--my right thumb/forefinger/third finger symptoms are certainly traceable to pressure on my right C6/C7 nerve root in the cervical spine, but I have no neck pain there.

Sometimes the symptoms of two different process are distinguishable, but sometimes not. One of the big problems with neuropathy is that symptoms that stem from brain/spine issues can be exactly mimicked by issues with more peripheral nerves--part of the reason our work-ups for cause are long, expensive, process of elimination, and not always fruitful.

Distal extremity pain is most commonly attributed to die-back, meaning that due to vascular insufficiency, such as is found in many autoimmune conditions, diabetes, and some toxic episodes, the fibers most distant from the heart of circulation are damaged/die first--the mechanism here is lack of oxygen/nutrients to the nerve and lack of removal of toxic wastes from it. But not all inflammatory processes work this way--some target specific areas (I can think of Sjogren's, Bechet's, polyarteritis nodosa, diabetic amytrophy, just off the top of my head), some are more global, and many toxic neuropathies are more body-wide.

That numbness you describe does sound like a vascular insufficiency--but it may just be a temporary compressive one, such as what happens when a limb "falls asleep". Of course, those of us with compressive nerve effects often find it easier to put parts to sleep, and fine it harder to "wake" them up.

The sad fact is there's a lot we don't know yet--until we can image down to the individual nerve fiber level, or individual capillary level, a lot of this is speculative.
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