Referred pain dr ahmed reda

PATHOPHYSIOLOGY OF REFERRED
PAIN
BY
AHMED REDA ABDEL-
HAMEED

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Contents
List of figures.............................................................................................................2
Abstract........................................................................................................................3
Introduction.................................................................................................................3
Pain ...............................................................................................................................4
Definitions..............................................................................................................4
Types of Pain:........................................................................................................5
Pain Receptors and Their Stimulation.............................................................6
Pain Receptors:.................................................................................................6
Three Types of Stimuli Excite Pain Receptors:.......................................6
Human memory.........................................................................................................8
Deﬁnition:...............................................................................................................8
Characteristics .......................................................................................................8
Referred pain........................................................................................................... 10
Definitions........................................................................................................... 10
Referred pain and radiating pain ................................................................... 11
Referred Pain Characteristics ......................................................................... 12
Pain Generators.................................................................................................. 13
Factors Favoring Referred Pain..................................................................... 15
Referred Pain Mechanisms ............................................................................. 16
Dermatomal rule: .......................................................................................... 18
Convergence– projection theory............................................................... 19
Examples of referred pain ............................................................................... 20
Dental clinical correlate........................................................................................ 21
Dental Causes of Tooth Pain.......................................................................... 21
Non-Dental Causes of Tooth Pain................................................................. 22
Conclusion ............................................................................................................... 23
Acknowledge................................................... Error! Bookmark notdefined.
References................................................................................................................ 25

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List of figures
figure1. 1 a woman grimacing...............................................................................4
figure1. 2Fast and slow Pain ..................................................................................6
figure1. 3Four types of sensory neurons and their receptor cells .................7
figure3. 1Cervical Medial Branch Blocks, Figure 3 a map of the referred
pain patterns from cervical zygapophysial joints at the segments
indicated. .................................................................................................................. 10
figure3. 2pain types ............................................................................................... 13
figure3. 3nociceptor pain...................................................................................... 14
figure3. 4C-fiber and A-delta fiber.................................................................... 15
figure3. 5referred pain mechanisms .................................................................. 17
figure3. 6 Dermatomal rule.................................................................................. 18
figure3. 7 Convergence– projection theory..................................................... 19
figure3. 8 Examples............................................................................................... 20
figure4. 1Referred pain from the wisdom molar............................................ 21
figure4. 2A nightguard protects the teeth......................................................... 22

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Abstract
As all medical professionals know, pain is the most common reason for a
personto consult a physician.
Under ordinary circumstances, acute pain has a useful, protective
function. It discourages the individual from activities that aggravate the
pain, allowing faster recovery from tissue damage. The physician can
often tell from the nature of the pain what its source is. In most cases,
treatment of the underlying condition resolves the pain. By contrast,
children born with congenital insensitivity to pain suffer repeated
physical damage and die young.
If not most, many dysfunctions of the bodylead to pain. Furthermore, the
ability to diagnose different diseases depends to a great extent on a
physician’s knowledge of the different qualities of pain. Forthese
reasons, we will concentrate on specific topics to reach how to understand
this we can say "complicated" topic.
Introduction
Pain and their subcategories in addition of the related subjects to them
will be discussed later here to obtain good and proper knowledge in seek
of understanding the complexity of the pain and our main topic the
referred pain.

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Pain
figure1. 1 a woman grimacing
Definitions
Pain Is a Protective Mechanism. Pain happens just if any tissues are being
damaged or alter its nature, and it causes the one to take action to try to
remove the stimulus. If we take a simple example that the one does every
day like simple sitting for a long time on the chair can cause tissue
damage the answer is because of blood reaches the tissues the skin will be
less as it is compressed bythe weight of the body on the vascular tissues.
When this happens we may as a result of the less blood flow or we may
say tissue ischemia, we simply shifts weight or change the position
subconsciously. But if another thing happens or develops like losing pain
sensation, like neural damage, spinal cord injury, pain sensation failure
and, therefore, fails to shift or change the position .This soonresults in
initiating tissues breakdown and desquamation of the skin at the areas of
pressure.
Another definition of pain is:
Pain is a complex phenomenon. It has been deﬁned by the Taxonomy
Committee of the International Association for the Study of Pain as “An
unpleasant sensoryand emotional experience associated with ongoing or
near tissue harm, or has been described in the way of such damage”
(MerskeyHandBogdukN(1994) Classiﬁcation of Chronic Pain, 2ndedn
.IASPPress,Seattle). It is often ongoing, but in some cases it maybe

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evoked by stimuli. Hyperalgesia occurs when there is an increase in pain
intensity in responseto stimuli that are normally painful. Allodynia is
pain that is evoked by stimuli that are normally on-painful. 1
Types of Pain:
Fast and Slow Pain
Pain could be classified into two main types: fast pain and slow pain.
Fast pain: After a pain stimulus is initiated or applied to the stimulating
area it will start feeling the pain within about 0.1 second.
Slow pain: here the durations differs only after 1 second ormore 1 second
from the applied stimulus and after that it start to increase slowly over
times and sometimes even minutes not seconds.
Fast pain has many alternative descriptions, like sharp, pricking pain,
acute pain, and electric pain. And all of these is felt just if a needle is
stuck into any area of the skin, when a knife applied to the skin, or when
burning of the skin occurs. Another example is the electric shock. Fast-
sharp pain is not felt in deeper tissues of the body.
Slow pain also has other terms, like to be mention slow burning pain,
aching pain, throbbing pain, nauseous pain, and chronic pain. This type of
pain is in most of times accompanied by tissue destruction. It could lead
to prolonged, unbearable misery. It may occurin the covering skin and
mostly in any investing tissue or organ. 2

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figure1. 2Fast and slow Pain
Pain Receptors andTheir Stimulation
Pain Receptors:
Types of receptors of pain located in the skin and other tissues are all
kind of free nerve endings. They are spreading widely in certain internal
tissues and also the superficial layers of the skins, suchas the periosteum,
the arterial walls, the joint surfaces, and the falx and tentorium in the
cranial vault. Most other deep tissues are only sparsely supplied with pain
endings.
Three Types of Stimuli Excite Pain Receptors:
Mechanical, Thermal, and Chemical. Pain can be stimulated by many
types of stimulus.
We could classify them as mechanical, thermal, and chemical pain
stimuli. Generally, the mechanical and thermal types of stimuli cause or
initiate the type of fast pain, while slow or chronic pain can be stimulated
by all three types. Some of the chemical substances cause the chemical

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one to occur are like bradykinin, serotonin, histamine, potassium ions,
acids, acetylcholine, and proteolytic enzymes. Plus, prostaglandins and
substanceP develop the sensitivity of pain endings but do not directly
cause them. The chemical substances play important role in enhancing
the slow, suffering type of pain that happens after tissue damage. 3
figure1. 3Four types of sensory neurons and their receptor cells

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Human memory
Definition:
Is an extensive and complex system. Memories are influenced by a
variety of processesoccurring at the time of encoding, the period of
storage and the context of retrieval. Many memories are consciously
accessible through language, and it is accepted that memories are
reconstructed and influenced by the characteristics of the to-be-
remembered material, and the conditions at the time of recall. There is
extensive evidence for the influence of implicit memories (material of
which the personis unaware) on behavior and experience.
Characteristics
Memory related to pain has not been deeply studied or investigated in
systematic approach, and it is only in recent that studies of memory
related to pain have begun to be known. Many studies have been
stimulated by important practical questions, concerning the accuracy and
reliability of retrospective clinical judgements of pain and improvement
as a result of treatment, but have lacked a strong theoretical rationale.
Other relevant questions concern the influence of memory for pain on
health behavior e.g. willingness to attend dental investigations, or other
potentially painful medical screening or diagnostic procedures. This essay
considers factors that influence memory for discrete events in which pain
is a defining characteristic, memory of persistent (chronic) pain, and
memories that are characterized by the somatosensoryre-experiencing of
pain. 4

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figure 2 1Pain Memory, Time course of two pain events - plotting pain intensity against time. See the text for an
explanation.

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Referred pain
figure3. 1Cervical Medial Branch Blocks, Figure 3 a map of the referred pain patterns from cervical
zygapophysial joints at the segments indicated.
Definitions
It is pain that translated from a location other than the site of the stimulus/
origin is causing tissue damage.
Also it is defined by Anderson, as it is “pain felt at a site different from
the injured or diseased organ or bodypart.”
Backing to the definition as we can see clearly here that referred pain still
has a lot of definitions. Another definition from Khalsa, who defines it as
“pain that exists in a location other than the immediate area of the spasm”

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without defining the limits, or the specific distributions. However,
according to him, Khalsa, the range of the main pain should not be larger
than the receptive field, which varies in size depending on the area of the
body. 5
Referredpain and radiating pain
It is important to differentiate between the referred pain and radiating
pain as the different is slight different we can say radiating pain is more
usually used in relation to that pain is being perceived in somatic and root
of spinal nerve distributions. We can say to sum up radiating pain is to be
considered as just a subcategory of referred pain.
Referred pain is the result of a group of interconnecting sensory nerves
that related to multiple different tissues. When there is a tissue damage at
a site in the group it is possible that when the signal reach the brain
signals are being interpreted around the nervous tissue.
Bellenir made an addition about this referred pain and adds “Antidromic”
into the definition, noting that visceral and somatic nerve cells may
synapse on the same neuron at the spinal cord. With repeated application
of the stimulation 'chronicity' “the impulse will spill over into the somatic
nerve”.
“Referred pain is a phenomenon that is frequently encountered and is
most baffling” stated by Warfield and Fausett as they called it
“heterotopic” pain.
"Pain is always subjective" as International Association for the Study of
Pain "IASP" Subcommittee said or stated when classified the referred
pain. But if you as a clinician or health professional does not recognize a
presenting pain pattern that your patient came with, where the pain is
already considered “subjective,” your chances of justly handling and
treating the patient are considered limited. So we come to this problem
where if psychogenic pain or as Subjective pain and referred pain become
synonymous, then the you as physician may get tired of looking for the
originating pathology which interfere with the propertreatment or any
treatment the patient gets. Doctorshopping this kind of the terms where
your patient then will enter till he receives the properdiagnosis and
treatment.

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Daunting challenge is diagnosis of the pathology of the pain especially
when the referred pain that being perceived is worse than the origin of the
pain. So you must put in your consideration all pain is to be always real.
So to achieve well understanding to achieve proper and accepted
diagnosis to achieve good treatment needs factors to perform that which
are understanding of the pain pathophysiology with familiarity of referred
pain possibilities in addition to physical and history data collection so we
finally achieve correct treatment. 6
ReferredPain Characteristics
For bestunderstanding of the characteristics of referred pain the best
example or pattern is referred pain patterns initiated from viscera and
myofascial trigger point areas.
Ludwig Ombregt has set a group of principles limiting and defining the
referred pain, the principles provided by him are:
1. Radiation of the referred pain is related to the spinal segmental.
2. The site of perceived pain and the pathology are on the same side of
midline doesn’tcross the midline.
3. Usually felt deeply not superficially felt.
4. Referred distally within a dermatome, but does not necessitate to be
throughout the dermatome totally.
5. Referred pain could be adjoining or sharing a common borderwith or
may be isolated from pain origin. In another meaning may be
"contiguous" or not.
Other add another principle to Ludwig Ombregt's principles which is the
tenderness they said that the site of the pathology is tender unlike the site
of the perceived pain which is not.
The only exception for these principles is Central pain phenomena which
doesn’tfit here. 7

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Pain Generators
figure3. 2pain types
We have three types we will clarify the Nociceptive, neuropathic and
central pain and the neural pathways.
According to the nociceptive pain, any stimulation must applied at area of
the free nerve endings with multiple types of signals being transmitted
through several basic nerve fiber types.

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figure3. 3nociceptor pain
Neuropathic pain is generated by dysfunction of pain nerves not like the
nociceptive pain.
Central pain is the description of dysfunctional perception of pain by
neurons in the origin which is spinal cord and/or brain.
Tenderness, hyperalgesia and/or allodynia all are used to differentiate
between the three types.
For the nociceptive pain to understand its generation well we need to first
know and identify the precise location of the free nerve endings of both
sympathetic C-fibers and A-delta fibers as they are where the nociceptive
pain is generated. We should know that the nerve fibers pathways on the
spinal dura does not by default predict us or confirm that the free nerve
endings also is placed or necessitated to be there. However, it is that they
are already in fact found in there, the potential spaceas they do in tissue
planes around the whole the body. 8

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figure3. 4C-fiber and A-delta fiber
Factors Favoring ReferredPain
Ombregt, in giving description to factors favoring reference of pain,
summarized that, from pooled experience, stronger central and/or
proximal deep stimuli has high index to cause pain beyond the pathology.
Sclerotomal referred pain has high incidence to occurthan myotomal
referred pain, and much more than bone pain to happen. This order of
occurrence may be in general diverse related to intensity and pain-related
dysfunction.
Marcus made another addition and says that "tenacious" pain stimulation
is more probably to be referred pain, superficial pain is probably to be
localizable (less likely referred), deep (excluding bone) is probably
referred one, soft tissue referred pain is not much localizable meaning
probably referred pain and distal pathology is much localizable than
proximal. 9

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ReferredPain Mechanisms
Just to mention that many authors like Ombregt, Marcus, Rachlin, etc.
discuss the embryologic role beyond the referred pain.
Nerve pathways and networks have tight relationship with the mechanism
control the referred pain.
Referred pain criteria has an evolutionarily ancient and developmentally
related to dermatomes, myotomes, sclerotomes and viscerotomes.
The mechanisms illustrating the referred pain are somehow not few but
we will mention the most known ones.
Rachlin refers to Selzer and Spencer. They suggested only five
mechanisms for it:
1. Convergence-Projection.
2. Peripheral Branching of Primary Afferent Nociceptors.
3. Convergence-Facilitation.
4. Sympathetic Nervous System Activity.
5. Convergence or Image Projection at the Supraspinal Level.
Additional terms mechanisms of referred pain:
1. Phantom pain.
2. Embryologic relationship of the internal organs to spinal levels. 10

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figure3. 5referred pain mechanisms

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The main mechanisms we will discuss later are the dermatomes and the
convergence-projection theory.
Dermatomalrule:
When pain is referred it is usually to a structure that developed from the
same embryonic segment dermatome as the structure in which the pain
originates. This principle is called dermatomal rule of referred pain.
Physiological distribution according to dermatomal rule is pain nerves at
spinal nerve roots.
FOR INSTANCE:
 The heart and the left arm (the inner aspect).
 Testicle & ureter plus kidney (from urogenital ridge).
figure3. 6 Dermatomal rule

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Convergence–projectiontheory
According to referred pain the second mechanism to be discussed shall be
convergence of somatic and visceral pain fibers on the same second-
order neurons in the dorsalhorn that expose to the thalamus and followed
by the somatosensorycortex.
Different afferents converge onto common spinal neurons8 and are
unable to be discriminated by higher centers. The mentioned theory
illustrates or states that the segmental bio nature of pain and also the
increased referred pain sharpness when stimulus is went higher.
This theory does not discuss or clear the delay in development of referred
pain or the hyperalgesia or that referred pain as being a bi-directional
phenomena.
Criticism of this model arises from its inability to explain why there is a
delay between the onsets of referred pain after local pain stimulation.
Experimental evidence also reveals that referred pain is usually
unidirectional. 11
figure3. 7 Convergence– projection theory

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Examples of referred pain
figure3. 8 Examples

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Dental clinical correlate
Referred pain or radiating play a major a role in relation to dentistry
especially to lower wisdom teeth.
figure4. 1Referred pain from the wisdom molar
Dental Causes ofToothPain
Teeth another thing that considered an example of the refer pain as they
can refer to other teeth plus to other anatomic areas related to the head
and neck. This may create a diagnostic challenge, in that the patient may
insist that the pain is from a certain tooth or even from an earache when,
in fact, it is coming from a faraway tooth with pulpal pathosis or
periodontal condition. Using electronic pulp testers, investigators found
that patients could localize which tooth was being stimulated only 37.2%
of the time and could narrow the location to three teeth only 79.5% of the
time, illustrating that patients may have a difficult time discriminating the
location of pulpal pain.
Referred pain from a tooth is usually stimulated by a severe stimulation
of pulpal C fibers, the nature of somehow slow conducting nerves that
when provoked result in an intense, slow, dull pain. Anterior teeth, the
central and lateral incisors plus the canine(s) rarely refer pain to the other
teeth or to oppositearches, unlike the posterior ones which can refer pain

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to the opposite arch or to the periauricular area or even to the temporal
area causing headache but seldom to the anterior teeth.
The lower posterior molars tend especially to transmit referred pain to the
periauricular area much more than upper posterior molars. To test that
clinically a study revealed that when the second molars stimulated with a
pulp tester (electrical), the patients discriminate preciously which arch the
lower or the upper ones the sensation is related to only 85% of the time,
compared with an accuracy level of 95% with first molars and 100% with
anterior teeth. The authors also pointed out that when patients first feel
the sensation of pain, they are more likely to accurately discriminate the
origin of the pain.
Especially in dentistry as it is resemble complicated part of the body the
oral and the maxillofacial area and because of the referred pain can make
it difficult to reach the correctdiagnosis and by the way the proper
treatment, the clinician or the dental professional must make sure to reach
a properdiagnosis to save the patient from unnecessary dental treatment.
Non-DentalCauses ofToothPain
Pain that is being felt in relation to teeth can be referred from many other
sources, like muscles, nerves and other parts of the human body. Now we
will mention examples of some possible non-dental causes that cause pain
in teeth:
 Nerve Disorders
 Temporomandibular Joint Disorder(TMD)
 Ear Infection
 Sinus Condition
 Jaw Clenching/TeethGrinding
figure4. 2A nightguard protects the teeth

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 Other Non-DentalCauses ofTooth Pain
Migraines are recurring headaches that are thought to be caused by
problems in the brain. A midface migraine looks like a traditional
migraine, but instead of happening in the forehead site, it is being
felt in the face, especially in the upper maxilla. Thus, it can easily
be confused with a toothache or a sinus problem. In addition to
migraine headaches, other non-dental causes of oral pain include
cluster headaches, shingles, and fibromyalgia and vitamin
deficiencies. Some non-dental causes of tooth pain are very
dangerous and could be fatal, like heart problems and lung cancer,
so dental pain should treated at face value. 12
Conclusion
Well knowledge about the referred pain is considered as a major
importance to locate the specific true origin of pain pathology in our way
of obtaining the properdiagnosis and treatment for the sake of the patient.
So a well-equipped physician or heath care professional with knowledge
and wide experience only could understand complex behind the referred
or radiating pain which considered as subcategory of referred pain.
Suggesting that complaints are “non-anatomic” or “non-physiologic” may
very well be a clear indication of the diagnostician’s limitations rather
than a true reflection of a patient’s pathology or psychological state. Here
comes the role of these well-meaning and intelligent health care
professionals, as it really does require a specially trained physician to
effectively decide the primary origin of a patient’s pain complaint and to
state the most proper treatment early as possible. This diagnostic exercise
is the essential first step in deciding on a theoretically-based and
pragmatically-possible and effective treatment plan. With enough
understanding, these kind of various pain etiologies and types are mostly
helpful in treating with nociceptive pain. In another meaning, these pain
origins and referral types of pattern usually resemble normal
neurophysiologic bio functioning and provide the patient and the
physician with the necessary data for setting a properdiagnosis and
treatment planes for this kind of nociceptive pain. However, reality is

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much more complex. The referred pain phenomenon itself is apparently a
“dyna-”neuropathic process that is, pain nerve dysfunction.
This conclusion now refers to the referred pain as a condition or a
problem with the wires/wiring or it can also be central, i.e. the
“perceptron”.

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References
1. SweetWH(1981)Pain10:275
2. "International Association for the Study of Pain: Pain Definitions". Archived from the
original on 13 January 2015. Retrieved 12 January 2015.
3. Stone AA, Broderick JE, Shiffman SS, Schwartz JE (2004)
Understanding Recall of Weekly Pain from a Momentary
Assessment Perspective: Absolute Agreement, Between- and
Within-Person Consistency, andJudgedChangeinWeeklyPain. Pain
107:61–6
4. Ombregt L. A System of Orthopaedic Medicine, 2nd Edition.
Churchill Livingston. 2003. 1360 pp
5. Kosek E, Hansson P (2003). "Perceptual integration of
intramuscular electrical stimulation in the focaland the referred pain
area in healthy humans".
6. Witting N, Svensson P, Gottrup H, Arendt-Nielsen L, Jensen TS (2000). "Intramuscular and
intradermal injection of capsaicin: a comparison of local and referred pain"
7. Feinstein B, Langton JNK, Jameson RM Experiments on Pain
Referred from Deep Somatic Tissues. J Bone Joint Surg 35A:981–
987
8. L. J. Geneen, R. A. Moore, C. Clarke, D. Martin, L. A. Colvin, and
B. H. Smith, “Physical activity and exercise for chronic pain in
adults: an overview of Cochrane Reviews,” in Cochrane Database
of Systematic Reviews (CDSR), vol. 4, 2017.
9. H. Eloqayli, “Subcutaneous accessorypain system (SAPS): A novel
pain pathway for myofascial trigger points,” Medical Hypotheses,
vol. 111, pp. 55–57, 2018.
10.H. Eloqayli, A. Al-Yousef, and R. Jaradat, “Vitamin D and ferritin
correlation with chronic neck pain using standard statistics and a
novel artificial neural network prediction model,” British Journalof
Neurosurgery, vol. 32, no. 2, pp. 172–176, 2018.

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11.N. Bogduk, “The Anatomy and Pathophysiology of Neck
Pain,” Physical Medicine and Rehabilitation Clinics of North
America, vol. 22, no. 3, pp. 367–382, 2011.
12.https://www.karamadental.com/wisdom-teeth.html

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