PAIN TYPES

 

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Nociceptive Pain-(twisted ankle, burn)

This is the term for normal physiologic pain.  There are microscopic sensors in the skin that respond to very intense stimuli.  The are also free nerve endings throughout the body that respond to inflammation seen with acute injury.  Signals from these sensory organs go through a special pain signalling pathway in the spinal cord which is distinct from that which communicates non-pain stimuli such as touch, cold, vibration and other sensations.  It is the activity of this pathway that causes the pain.  Glutamate and Substance P are two of several neurotransmitters that modulate the forward transmission of pain stimuli through this pathway to the brain.  

Visceral Pain- (i.e. kidney stone, appendicitis)

This refers to pain emanating from our gut as well as other internal organs. Unlike the skin or limbs, there is no additional input from fine touch sensors; therefore, we cannot easily localize the source of the pain. When the pain is acute or intermittent, there is often an inflammatory component.  When chronic, it is often due to nerve damage or just a sensitivity to
 intetestinal muscle function (i.e. irritable bowel syndome)

Opiates are helpful for this pain but can easily backfire.  The constipation caused by them can make the pain worse.  The nausea and/or cramping associated with their wearing off can often be mistaken for a recurrence of the underlying pain and leads to continual and/or increasing drug use.  This can cause patients more discomfort than the original problem.  

Neuropathic Pain- (shingles pain, pain related to nerve injury in back or neck, trigeminal neuralgia)

This is a type of pain that occurs secondary to nerve injury.  After injury the remnant pain nerves may fire more often.  Additionally, the specialized pain tracts in the spinal cord react too easily to the primary pain nerves coming from the body; they fire more often causing more pain.  This lowered threshold may be due to abnormal processing of glutamate and substance P.  The result is that stimuli that are supposed to be mildly uncomfortable are more uncomfortable.

There is also an attempt for an injured nerve to reestablish connections in the spinal cord. Many times, these connections are faulty and injured sensory nerves connect with the pain tracts by mistake.  The result is that normal sensation will be sensed as painful sensation. 

It seems that the above abnormalities can get locked in for a long time.

Compared to other pain types, neuropathic pain is relatively insensitive to opiates BUT opiates may give still give significant relief.  Medicine like neurontin and lyrica are able to reduce the signalling from glutamate and substance P.  This is why they are useful for some patients with this type of pain.

Sympathetically mediated pain -Causalgia or reflex sympathetic dystorphy

This is a subset of neuropathy where the injury and/or abnormal signal processing affects the sympathetic nerves.  These are the nerves that control blood flow, temperature, sweats and other functions in the body.  For this reason, the pain is associated with abnormalities in
swelling, temperature changes, and color changes in arms/leg. 

This can be an intense pain and is very difficult to treat

 

 Myofacial pain

This referrs to pain that seems limited to the muscles and or their connective tissue. There is often a component of muscle spasm.  It may be due to injury although sometimes it is more chronic. 

The inflammatory component is one reason that doctors do trigger points; it reduces inflamattion in a targeted area.  Also, when these areas are numbed by novocaine, the muscle spasm may resolve.  

Fibromyalgia 

This is a poorly
understood disease.  There seems to be a
n abnormality of the central nervous system in which pain impulses are not being appropriately processed and the secondary nerves in the spinal cord fire too easily.  Since the problem seems to be in the secondary nerves, we have often presribed neurontin and/or lyrica which help reduce this type of nerve transmission.

Headache

Another syndrome of pain that is hard to characterize.  There many be components of muscle spasm, myofascial pain, inflammation from leaky blood vessels and/or neuropathy.  Treatments are varied depending on what the doctor believes is going on.  Unfortunately, it often means the doctor's bias rather than the true nature of the pain (which can be hard to discern) runs the course of treatment.

SUMMARY

When there is chronic pain there will usually be some component of neuroadaptation: changes in the central nervous system that serve to facilitate pain.  This may lead to pain hypersensitivity.  And remember, the use of opiates, which result in tolerance and withdrawal, may cause a rebound increase in pain signalling and increased pain when the drugs wear off.

 

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