Understanding Chronic Pain
people think of pain as coming from some physical or external source—a
broken bone, herniated disc, sprained ligament, or tumor—for example,
and that relieving the pain is as simple as addressing the cause. This
is known as nociceptive (no-see-SEP-tive) pain. Nociceptive pain is
usually caused by something outside the body.
usually directed at identifying the cause (typically some mechanical
problem such as a chronic sprain or strain) and fixing it.
the nervous system itself can also generate and perpetuate pain without
any ongoing stimuli from injury. This is known as neuropathic
(nur-o-PA-thic) pain. Examples of neuropathic pain include diabetic
neuropathy, postherpetic neuralgia (pain from Shingles), phantom limb
pain (pain in a limb that has been amputated), trigeminal neuralgia,
and sciatica. Neuropathic pain is often puzzling and frustrating for
both patients and physicians because it seems to have no cause,
responds poorly to standard pain therapies, can last indefinitely and
even escalate over time, and often results in severe disability.
pain is caused by a breakdown in the body’s ability to regulate or
modulate pain signals. The result is that pain signals that normally
would lessen or go away over time actually worsen and persist.
Four types of neuropathic pain
four most common types of neuropathic pain are direct stimulation of
pain-sensitive nerve fibers, automatic firing of damaged nerves,
deafferentation, and sympathetically mediated pain.
Direct stimulation of pain-sensitive neurons
primary sensory nerves that carry pain signals are called C-fiber
nociceptors. They fire in response to mechanical stretching or
compression and to certain inflammatory chemicals secreted in the body.
tumor compressing or stretching a nerve can produce pain that is
perceived in the distribution area of that nerve. Lumbar disk
herniation with its accompanying chemical irritants to the adjacent
nerve root can produce sciatic nerve pain. Carpal tunnel syndrome is
due to a combination of repetitive stretching of the median nerve,
compression caused by swelling, and inflammation producing chemical
irritation of the median nerve.
In each of these examples,
treatment is aimed at alleviating mechanical or chemical irritation
typically through physical therapy, the use of various medications,
resting (splinting) the affected body part, or surgical decompression.
Automatic firing of damaged nerves
pain from an injury has persisted for a long period of time (usually
longer than 6 months), the nerve itself undergoes chemical and physical
changes resulting in spontaneous nerve firing, even without any
stimulus. Resulting pain is often described as lancinating
(knife-like), stabbing, or shooting. When many nerve fibers are
affected and fire erratically, neuropathic pain has a quality of
continuous burning. This process of automatic firing can last
indefinitely and represents one cause of persistent physiologic pain.
in the face of persistent pain, the centers in the brain that perceive
and modulate pain become sensitized, and pain can be experienced
continuously, even in the absence off any cause.
normal conditions, sensations are transmitted from peripheral tissues
by way of a connected chain of nerves in the spinal cord, brain stem,
and brain. Interruption (deafferentation) of any portion of that chain
provides the potential for increased irritability and firing of nerves
further up the pathway. This phenomenon explains how phantom limb pain
can occur: Loss of sensory input from a limb can produce spontaneous
firing of second- and third-level neurons, resulting in pain and other
sensory experiences in the missing limb.
damaged by diabetic neuropathy, post-herpetic neuropathy, or peripheral
nerve trauma may generate firing in the higher-order nerves and, thus,
ongoing pain. A stroke causing a strategic lesion in the pain pathway
can result in ongoing deafferentation pain that is experienced at one
body site but is generated at the infarct site or further along the
pain transmission pathway.
Sympathetically mediated pain
painful stimulus can trigger increased activity in a certain portion of
the nervous system known as the autonomic nervous system (consisting of
the sympathetic and parasympathetic systems). The autonomic nervous
system controls involuntary physiologic processes such as heart rate,
sweating, constriction of blood vessels, and digestion. Thus, injury
often initiates regional changes in circulation and temperature. The
first response often is warming and increased circulation in the
injured area, probably to aid the inflammatory response. However, the
autonomic nervous system can continue to respond in a changing pattern
of sympathetic hyperactivity. Changes such as cooling of the skin,
sweating, and regional circulation abnormalities can be seen.
Treating Chronic Pain
of the cause, it is important to realize that no pain medication exists
that will completely eliminate pain! The goal is to reduce the pain to
a more manageable level.
Nociceptive pain responds generally well to the various pain medications—anti-inflammatories, Tylenol, narcotics, etc.
most traditional pain medication is less effective in treating
neuropathic pain than treating nociceptive pain. Anti-inflammatory
medications, such as Motrin or Alleve, and narcotic-based medications,
such as codeine, Oxycontin, Vicoden, etc., help only a little. In fact,
taking too much narcotic medication can actually make the condition
Medications that help control excess nerve firing
seem to work better. They help by decreasing the irritability or
sensitivity of the nerve fibers. Various anti-depressant medications
often are used, most commonly amitriptyline (Elavil®), nortriptyline
(Pamelor®), and Cymbalta®. The antidepressants work by affecting
neurotransmitter function. Neurotransmitters are chemicals released
from the end of one nerve cell and picked up by the next nerve cell,
thus transmitting a nerve impulse from one nerve to the next. Certain
neurotransmitters have a calming effect, and select antidepressants
increase the amount of these calming neurotransmitters.
newer class of medications, derived from epilepsy medications, holds
new hope for treating neuropathic pain. Gabapentin (Neurontin®) has
been used for a number of years successfully. But a newer medication,
pregabalin (Lyrica®), seems to work even better. Your doctor can
discuss these with you.
Muscle relaxers can be helpful, but they tend to make you sleepy or disoriented.
therapies, such as TENS units, and even surgically implanted spinal
cord stimulators, can be used. Electrical therapy works by stimulating
one type of nerve fiber to block pain coming from another type of
fiber. This is similar to when you bang your elbow, you rub it to make
it feel better. Rubbing it stimulates one type of nerve fiber that
partly “blocks” the transmission of fibers carrying the pain signal.
goal of physical therapy is to help reduce the pain and enable you cope
and manage better with it. Therapy is designed to help improve and
maintain your strength and flexibility, since progressive weakness and
stiffness can further aggravate the pain, and even cause other painful
problems. Improving the strength of the affected area and surrounding
areas also helps relieve stress and strain on the ligaments, joints,
and other structures.
The most effective type of therapy for
chronic pain is functional therapy, that is, therapy designed to
improve your function. This includes various exercises to improve your
movement, strength, balance, coordination, muscle firing, and so on.
For the most part, the use of “passive modalities,” such as hot/cold
packs, ultrasound, and electrical stimulation, provides no lasting
benefit in the treatment of chronic pain. These modalities may make you
feel better briefly, but they rarely help in the long run.
Unfortunately, many physical therapy groups like to rely heavily on
these passive modalities because they are easy to apply, require little
therapist involvement, and get reimbursed nicely by the insurance
treatments, such as Osteopathic Manipulative Treatment, chiropractic,
acupuncture, massage therapy, Reiki, Therapeutic Touch, and so on all
can be useful additions to a comprehensive treatment program for
treating chronic pain. Again, none of them will eliminate the pain, and
not all approaches work for all patients. It is unfortunately
Chronic pain is a
challenging medical condition that often defies even the most
well-intentioned physician. Rarely is complete pain relief realized.
Treatment requires a multifaceted, multidisciplinary approach. The goal
of treatment most commonly is reducing the pain to a manageable level,
and improving the patient’s functional ability in order to continue
with tasks or work, home, and daily life.
Resources for Chronic Pain
Belgrade, MJ. "Following the Clues to Neuropathic Pain." Postgraduate Medicine. 1999;106(6):127-40.
Weisberg MB, Clavel AL Jr. "Why is chronic pain so difficult to treat?: psychological considerations from simple to complex care." Postgraduate Medicine 1999;106(6):141-164.