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Table of Contents
acute - lasting a short, or brief, period of time
allodynia - pain due to a stimulus that does not normally cause pain
antiarrhythmic - medications used to treat irregularities in
the rhythm of the heart
anticonvulsants - medications used to prevent seizures
antidepressants - medications used to treat depression
causalgia - a constant, burning type pain
chronic - occurring for a long period of time
diabetic neuropathy - nerve damage as a result of diabetes
dysesthesia - an unpleasant, abnormal sensation
hyperalgesia - an exaggerated response to a painful stimulus
hyperesthesia - abnormal sensitivity to stimulation
myofascial pain - broad group of muscle disorders which involve pain
- in various muscles of the body - caused by super sensitive trigger points
narcotic - class of drugs derived from the opium plant -
or created synthetically for the same effect; used as pain-killers
neuropathic pain - pain due to nerve damage
nociceptive - pain in response to an unpleasant or damaging stimulus
NSAID - non-steroidal anti-inflammatory; class of pain relieving
drugs which includes ibuprofen, naproxen (Alleve), and others
opioid - narcotic
PND - painful neuropathic disorder; any painful disorder where the
pain is caused by nerve damage; such as diabetic neuropathy or
post-herpetic neuralgia
paresthesia - abnormal sensation
post-herpetic neuralgia - painful nerve damage as a result of
"shingles" (herpes zoster) |
"Patients who have chronic neuropathic pain [often]
have more than one type of pain. For example, a man who has
post-herpetic neuralgia at high and mid thorax may have constant ongoing
pain that keeps him awake all night; mechanical allodynia and hyperalgesia
that prevent him from wearing any clothing so he cannot be active and
socialize; secondary myofascial pain in the shoulder so that use of
that arm is limited; and after a few short weeks of his pain, the patient is
by now sleep deprived, depressed, anxious, and very irritable." (Backonja
and Galer, Neurol Clin 1998;16).
One could easily substitute Chiari or
syringomyelia for post-herpetic neuralgia in the above quote and still have
an accurate description. Pain, most often neuropathic pain - meaning
due to nerve damage - is a common, serious, and difficult to treat problem
for the Chiari and syringomyelia community. It is likely that many
readers can relate to issues such as burning pain for no reason, abnormal
response to touch or temperature, and lasting muscle pain, all of which at times seem
immune to any treatment.
While the phrase misery loves company may or may not
apply here, the fact is that C&S patients are far from alone in enduring the
unrelenting, unwanted presence of neuropathic pain. People can develop
neuropathic pain for numerous reasons (see Table 1) from surgical
complications to immune system diseases to infection. Because of their
prevalence, the most studied causes of neuropathic pain are diabetic
neuropathy and post-herpetic neuralgia.
As the opening quote from a pain study indicates,
understanding, diagnosing, and treating neuropathic pain is not easy.
There are many different types of neuropathic pain, each with different
features, and different responses to treatment. In addition,
identifying the underlying cause of the pain is often not enough, as two
people with pain from the same syndrome, such as syringomyelia, often have
different pain symptoms and will require different treatments.
Types of Neuropathic Pain
As is often the case when a medical subject is not
completely understood, terminology becomes a problem. However, to
understand neuropathic pain, it can be broken down into different types.
At the highest level, neuropathic pain is a result of damage to either the
central nervous system (meaning the spinal cord and brain) or peripheral
nerves (the actual nerve fibers which run throughout the body). In
addition, the pain can be in response to a stimulus (such as touch or
temperature) or arise on its own (spontaneous pain).
Stimulus driven pain is often referred to as
hyperalgesia, which is an exaggerated response to a painful stimulus; or
allodynia, which is pain from something which normally does not cause pain.
An example of hyperalgesia is when a small pinprick results in a sharp,
stabbing pain, or when the touch of a cold object causes a painful burning.
An example of allodynia is when something as innocuous as the light touch of
clothing is painful and unbearable.
Spontaneous pain, which can be either constant or
intermittent, is often described as shooting or burning pain, which happens
for no apparent reason. Of course, in the world of neuropathic pain,
nothing is simple and many people suffer from a mix of both stimulus driven
and spontaneous pain. Paresthesia, which is an abnormal sensation such as a
tingle, and dysesthesia, which is an unpleasant, abnormal sensation are good
examples of this complexity, as they can arise either spontaneously, or from
stimulus.
Underlying Mechanisms
Although the exact mechanisms behind neuropathic pain are
not completely understood, there are several theories on how different types
of pain can develop. In looking at the peripheral nervous system,
tissue damage to a certain part of the body results in a complicated series
of actions centered around the inflammation process. As the body
releases different chemicals to deal with the damage, the presence of these
chemicals can make the nerves which carry pain signals back to the spine and
brain extra sensitive. Once sensitized in this fashion, the nerves do
not go back to their natural state. This type of sensitization often
results in hyperalgesia, or the exaggerated response to a painful stimulus.
The spinal cord itself can also be the source of pain
problems. It is thought that certain cells in the spinal cord (the
pain receptors) are fundamentally altered when exposed for too long to a
true, painful stimulus. Thus, once the nerves in the spinal cord are
altered, even if the original source of the pain is alleviated, problems can
occur. This can lead to allodynia, or the painful response to
something that shouldn't be painful. When a person with allodynia
"feels" the touch of a shirt, for example, the signal is carried properly
from the nerve endings to the spine, but then it is misinterpreted as pain.
How the nervous system changes over time in response to pain is extremely
complicated and is just beginning to be understood.
Spontaneous pain, often described as burning in nature,
is thought to occur when nerve fibers send extraneous signals. This
can be from nerves losing their protective covering, or from
chemical-electrical imbalances that develop, causing improper firing of the
nerve cells.
Diagnosis and Treatment
Identifying and diagnosing the specifics of
someone's neuropathic pain requires a thorough examination, including a
history, physical, and neurological evaluation. By taking a complete
medical and surgical history, a doctor can identify potential sources of the
pain, be it from an acute injury, diabetes, or syringomyelia. A
physical exam allows the physician to begin to pinpoint which parts of the
body are affected and what parts of the nervous system may be involved.
Finally, a neurological exam is used to see how someone responds to
different stimulus, such as light touch, cold, heat, pressure, and pin
pricks. At the end of a thorough evaluation, the treating physician
should have a pretty good idea of the source and type of pain that is being
dealt with.
Unfortunately, treatments for neuropathic pain are not
easy to come by. Most drugs used to treat neuropathic pain were
developed for other conditions and are prescribed for pain "off-label".
Anticonvulsants (seizure medicines), antidepressants, and antiarrhythmics
are categories of drugs commonly used to combat neuropathic pain. For
example, the popular drug Neurontin was originally developed as an epilepsy
drug, has since been approved by the FDA to treat post-herpetic neuralgia,
but is commonly prescribed for many different types of neuropathic pain.
Because the drugs are prescribed off-label, large
studies evaluating their effectiveness are few and far between. There
is some research however, demonstrating that certain drugs may be effective
for certain types of pain. Gabapentin, for example, has been shown to
have some effectiveness in treating hyperalgesia and allodynia.
A completely different class of drugs, namely opioids
(or narcotics), are sometimes prescribed for pain. Because of addiction
issues however, their use is still somewhat controversial. In
addition, many people find the benefits of narcotics are not worth the many
side effects they can incur.
Whether it's antidepressants, narcotics, or non-drug
treatments such as physical therapy and acupuncture, the current state of
treating neuropathic pain is largely comprised of trying things and seeing
what works. Unfortunately, the results are often less than stellar and
neuropathic pain remains stubbornly difficult to treat.
The Future
For the time being, the burden remains on the
neuropathic pain patient (in conjunction with their doctors) to evaluate the
different treatment options and see what works best for themselves.
The good news is that there is a growing recognition of the magnitude of the
chronic pain problem. According to Congress, we are living in the
Decade of Pain Control and Research, and pain is now widely viewed as the
fifth vital sign in the medical community. In addition, because of the
millions of people who suffer from chronic pain, there is a tremendous
economic incentive to develop new treatments, and drug companies all over
the world are actively working on identifying and developing new pain drugs.
Sources:
- Harden RN.Chronic neuropathic pain. Mechanisms, diagnosis, and
treatment. Neurologist. 2005 Mar;11(2):111-22
- Dworkin RH. An overview of neuropathic pain: syndromes,
symptoms, signs, and several mechanisms. Clin J Pain. 2002
Nov-Dec;18(6):343-9.
- Backonja MM, Galer BS. Pain assessment and evaluation of patients
who have neuropathic pain. Neurol Clin. 1998 Nov;16(4):775-90
--Rick Labuda
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Key Points
-
Neuropathic pain is a common,
lasting problem for Chiari and syringomyelia patients
-
Neuropathic pain is complex and most
people usually have several types of pain
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Pain can be from an exaggerated
response to a stimulus, or spontaneous in nature
-
A careful and thorough exam is
necessary to classify the types of pain a patient has
-
Most treatments for neuropathic pain
are based on using drugs designed for other purposes
-
There are limited studies showing
which of these drugs are effective for which types of pain
-
There is a growing awareness of the
issue of chronic pain and drug companies are actively researching new
neuropathic pain treatments
Table 1
Possible Causes of Neuropathic Pain
Source: Harden
RN.Chronic neuropathic pain. Mechanisms, diagnosis, and treatment.
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