Friday Tidbits: How Pain Meds Work, Pt 2

Hippocrates: "First Do No Harm..."

I suffer with a chronic painful condition, but I am not alone.  It's a shocking statistic that a third of the world's population suffers from persistent or recurrent pain.  It's been estimated that this costs the American people alone approximately a hundred billion dollars annually in healthcare, compensation and litigation.  And yet, despite the enormity of this problem, there is much that needs to be understood about chronic pain. 

First, let me say that "chronic" pain differs from "actute" pain because different mechanisms are in play. There are other types of pain, such as neuropathic pain, which exists without any obvious trigger, such as you would find in acute pain, caused, for example, by a fall or blow to a part of the body.  However, even acute pain is not completely understood.  For example, we understand that when a body part is injured or about to be injured, pain signals travel from receptors in the skin or muscle, which are known as "nociceptors."  (Hang in there, people!  We'll shortly be getting into some heavy science here, but fear not, I'll try to be your guide here as best I can!  Besides, if *I* can understand it - sort of - so can you!)

With acute pain, there are different kinds of nociceptors which are associated with different kinds of nerve fibers.  One type is called the A-fiber.  This nerve fiber has a very thin coating of a protective chemical called myelin - famous to us because of it's role in MS.  This fiber, when activated, creates a fast, piecing kind of pain. 

On the other hand, there's a different fiber called the C-fiber, which has NO myelin on it, and it transmits a slower, burning type of pain. (We're still dealing with "acute" pain here!)  So far, TWO classes of C-fibers have been found.  One class contains a range of neuropeptides - neurotransmitters, if you will - including Substance P and calcitonin gene-related peptide (again, all neurotransmitters).   It also expresses a receptor for another important chemical called "nerve growth factor," which also helps in the pain transmission process (not good, in other words!).

A second C-fiber class contains fewer neuropeptides (neurotransmitters) and mediates a different type of pain than the class described above.  Once the pain is transmitted to the thalamus and other parts of the brain, the pain signals are interpreted and modulated.  Some people have the ability to block out some pain signals better than other people. There are actually cells in the spinal cord which prevent pain signals from reaching the brain. They are called "inhibitory interneurons."  Some people have a lot of these cells and are able to feel less pain than others. This may be why there is a wide variation in how people register pain and may actually explain the differences in pain threshold from person to person.  (Believe it or not, but this is definitely the Cliff Notes version!)

Chronic pain differs from acute pain in that the patient has had the pain for a relatively long period of time (authors disagree on the exact length of time but most agree it is between 3 and 6 months).  For chronic pain to persist, there does not need to be a series of inciting facts such are repeated traumas.  Chronic pain involves a fundamental change in the nervous system including neuroplasticity, which is described below. The A-fibers and the C-fibers are not major players here.  So, why go on and on so much about the acute pain?  It's nice to understand what you DON'T have.  I always feel that knowledge is power.

Not surprisingly, there does seem to be some confusion as to why certain medications are used for certain pain states as opposed to other types of medications.  It's widely accepted by the medical community that although morphine-type narcotics can be very useful in acute and in some chronic pain states, they tend to be not very effective in neuropathic pain.  Neuropathic pain comes about when there is some underlying medical problem such as diabetes or shingles.  In neuropathic pain, the pain is not useful in the sense that it doesn't warn you about imminent tissue injury, such as putting your hand on a hot stove.  It's even more complicated than that.  The nervous system itself is sending weird signals like burning and even itching to the brain.  Many patients with neuropathic pain receive anti-depressant medications and/or anti-epileptics to help control the pain.  Some researchers believe that patients who have neuropathic pain actually have fewer opioid receptors expressed on the nociceptors and spinal neurons (nerve cells).  Whatever the reason, this pain is difficult to treat.

As if things couldn't get any more complicated, one must not forget the entity known as "phantom limb pain," which is due to actual changes in the brain itself.  The patient feels pain in a limb that is no longer there.

Note: This is an example of brain neuroplasticisy where the brain actually changes in how it processes and registers pain.  The pain of many fibro patients is believed to be due to this phenomenon which may help explain why fibro can be treated but not cured.  The brain, unfortunately, has actually changed, as can be seen in brain-imagining studies.

This may also explain why different types of pains in the same person responds differently to different types of medication.  For example, a person with migraine headaches who also suffers from back pain may need more than one type of med to treat both problems even though one might think pain is pain and that both conditions would be helped by a pain medication like morphine.  

Quite the opposite is true. The migraine type of pain tends to respond to a family of drugs called "triptans." Here is a type of pain which is pretty much understood!  We now have "triptans" which include Imitrex, Frova, and Axert.   Triptans are thought to work on the brain circulation to make it more normal so the headaches can be treated effectively.  However, these medications don't work on back pain, which is typically mediated through nociceptors and neurotransmitters like Substance P.

I so wish that doctors and the medical community could appreciate this well-understood part of medicine so much better.  For example, I was once hospitalized for some sort of problem - who can even remember why or what at this time?  YOU think YOU need a scorecard in trying to keep things straight.  Here's a bit of a secret: *I* need a darn scorecard even more!

As an example, though I'll explain the circumstances at another time, under "humorous events": Suffice it to say that during this particular hospitalization I needed pain medication for my regular fibro and CFIDS/CFS/ME issues, which I was given.  However, I also had huge pain in my back which wasn't helped by my "usual" meds.  This was pain that resulted from the lack of Human Growth Hormone (HGH).  This lack of the highly-regulated HGH  (which we couldn't even pay for it ourselves) caused my spine to become eroded and discs to deteriorate, while we couldn't get the HGH for two years, by any means tried and despite the fact that I passed the "gold standard" test with flying colors!

Moving on, the arrogant nurse who came to my room felt that I didn't need the added pain medication (already ordered by my doctor!) and promptly gave me a lecture on how serious it was that I was in the hospital for detoxing!  Excuse me?  Shut your mouth first and secondly, follow doctor's orders!  Furthermore, reading my chart wouldn't be amiss as well!  Hubs got a middle of the night call from me blubbering that I needed to go home NOW, my doctors who knew me and my case inside and out were displeased to be called by a hospital staff member who felt he should be some sort of "missionary" for the misguided, moi.  Said missionary could not begin to understand that different meds work on different nerve paths and that the problems I was having was a perfect example of that.  Being a mere patient, he also didn't want any "excuses" from me when I tried to explain how pain meds work, and gave me a lecture about that as well!  

I'm only grateful that this was in a well-regarded local hospital where the bureaucracy was little and not in a "major medical center" where they claim to know much but are sorely lacking in the non-sexy departments which - interestingly enough - don't bring in the big bucks when it comes to fund-raising.  Nor DO they care, as I found out through the many lengthy hospitalizations my daughter had to endure.

So there you have it, a bit more of how pain meds work or don't work.  I hope this helps - especially since I'm not able to write up these sorts of medically sophisticated posts too often!  They are killers!  (Joke!)

As always, wishing that everyone is feeling their best, only better.  Ciao and paka.


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