Download Varicella Zoster

Types of pain:
1- Nociceptive pain, divided into
A) Somatic : most often presents as throbbing and well localized pain and
responds well to NSAIDs.
B) Visceral: Can manifest as a referred (coming from other structures) or a well
localized pain.
2- Neuropathic pain
Pain that is associated with actual physical nerve damage or irritation.
More Details regarding those two types would be mentioned later.
The five stages of nociception are stimulation, transmission, modulation,
perception and adaptive inflammation.
* Pain transmission:
Different neuronal fibers transmit pain's signal as an action potential to the brain.
The larger the diameter of the fiber , the more insulated it is and the faster the signal
transmission is through it. Nociceptive transmission takes place in Aδ and C nerve
fibers.
A delta (Aδ) fibers have large diameters, they're myelinated and are responsible for
rapid conduction of electrical impulses associated with thermal and mechanical
stimuli, where there is a risk of severe tissue damage if the response is delayed.
E.g.: in the case of burning, a thermal stimulus, a delayed response would lead to
significant tissue damage and to avoid unnecessary and maybe life threatening
injury, the signal must be conducted as soon as possible to allow for an immediate
reflex. A reflex means that the signal needn't get to the brain and the spinal cord
would mediate a quick response through motor neurons.
The pain associated with this type of neuronal fibers, Aδ, is usually described as
intense, acute and of sharp or stabbing nature that alerts the subject to injury or
insult to tissues.
However if the trigger is not life threatening , although irritating to the subject , the
impulse is transmitted via C fibers; unmyelinated fibers that are small in diameter
and release glutamate(excitatory neurotransmitter in the brain), substance P and
CGRP which is a peptide in the brain associated with stimulatory pathways and
headaches.
Fibers C convey mechanical and thermal signals that are not life threatening or do
not cause immediate and serious injury to the body , like neuropathic pain as in the
case of diabetic neuropathy , which is uncomfortable to the patients due to tingling,
numbness and burning sensation but it is not life threatening and doesn’t require a
fast response in milliseconds.
The pain associated with this type of neuronal fibers, C fibers, is usually described
as dull (not specified or localized) , aching and burning pain and sometimes it is
called the second pain, because it is perceived after the first pain sensation which
was mediated by A delta fibers. An example is patients with MI, where pain would
radiate to other areas. The second pain , is pain that occurs after the initial pain
signal , and it is transmitted through C fibers.
Keep in mind that both fibers are parts of the same system but each specifies for a
specific physiological function.
A potential intervention in this phase would be to block the stimuli from binding to
the nociceptive receptors (the pain triggering receptors at the neurons) then the pain
could be modulated.
*Modulation of the pain signal:
happens when the signal reaches the spinal cord to move on to the brain , and
either excitatory or inhibitory neurotransmitters are released and here is where the
pain signal, regardless of the initial stimulus, is modulated.
* Pain Perception:
Perception is the processing of the pain signal that occurs in the brain and it differs
from an individual to another.
For example, an emotionally healthy, happy man would have a higher pain
threshold. Meaning that while the same stimulus that causes him mild to moderate
pain would cause someone with physical or psychological issues severe pain
because he would have a lower pain threshold and a higher susceptibility to pain.
The reason behind that is that the processing in the brain , the perception, differs
between them.
*Adaptive inflammation
After the person is subjected to an injury , an acute inflammation takes place, where
inflammatory mediators are released. Those inflammatory mediators trigger pain ,
by binding to the nociceptive receptors thus decreasing the pain threshold, making
the injured area more sensitive to pain, ultimately decreasing the movement of the
afflicted area and optimizing its healing.
After healing, the inflammation should subside along with the pain. Although,
sometimes maladaptive inflammation occurs and pain persists despite healing
resulting in a type of neuropathic pain called functional pain, where actual damage
or pain triggers are absent but improper pain signals are present making it self
sustained (without a trigger).
In nociceptive pain the treatment aims to cure, while in neuropathic pain the target is
to improve or regain functionality in the afflicted part as cure is unlikely achievable
by pharmacologic or nonpharmacologic treatments unless there is an obvious
reason for the nervous damage and it is corrected via surgery , such as in the case
of degenerated discs operations , as a vertebrae compresses a nerve and results in
neuropathic pain and pharmacologic agents couldn't result in a cure , a surgery
would target the reason for the damage allowing the healing and recovery of the
nerve.
Classification of pain, according to duration and prognosis:
1- Acute Pain:
Caused by surgeries, acute illnesses, trauma and labor.
Acute pain usually is nociceptive and lasts from a few hours up to months, but never
more than 6 months and can be successfully managed with NSAIDs, especially the
somatic kind.
2- Chronic pain is defined as pain that persists for 6 months to several years. It
serves no biological protective purpose causing undue stress and suffering.
- Insomnia and depression are unusual in acute pain but common in the case of
chronic pain.
As the psychological component is a major issue in chronic pain, the key to a
successful management rests on the prevention and elimination of unnecessary
suffering and despair. Using cognitive interventions and physical therapies as well
as pharmacologic agents is helpful.
While nociceptive pain usually results in acute pain, neuropathic with chronic pain ,
but exceptions are present in both cases.
An example of acute neuropathic pain is in the case shingles, caused by the
Varicella Zoster virus. It causes moderate to severe pain , usually severe that lasts
for few days. Even with supportive treatment with an antiviral, the virus won't be
eradicated, but the pain would subside( typically within two weeks).
The main difference between acute and chronic pain is predictability, ,ie , the ability
of the patient or health care taker to predict the type , severity and duration of pain
from day 1; as long as the progression is known or predictable it is considered acute
pain , if it couldn’t be predicted even from day 1 , then it's considered chronic.
Example : In a patient with pharyngitis, from the first day it's known that the peak of
pain would be in the first couple of days, in three to four days it will diminish or
decrease gradually and in 7 to 10 days it will be gone even without antibiotic
treatment and since the progression of the pain is know, it is called acute pain.
While if a patient has diabetic neuropathy , it is unknown whether the intensity and
the pattern of the pain will change and a remission is unpredictable, classifying it as
a chronic type of pain.
Treatment:
First line of treatment for neurologic pain is drugs that stabilize neuronal membranes
to prevent the travelling of impulses and action potentials , thus treatment with
anticonvulsants or antiepileptic drugs and antidepressants such as TCA or SSRI is
recommended.
The treatment of nociceptive pain depends on its the severity.
There are several tools or scores that evaluate the severity of the pain , but always
keep in mind that pain is very subjective and depends on the patient in the first
place.
The facial pain score is one of the most famous tools to evaluate the severity of the
pain, it categorizes pain into grades from 1 to 10.
Zero indicates the absence of pain, 1-3 mild/minor pain, 4-6 is moderate pain and 710 indicates severe pain.
To consider the pain medication effective , it should reduce the pain by 1 category (
severe to moderate or moderate to mild). (A reduction from 10 to 8 is considered
ineffective).
Ideally a goal of mild to no pain is aspired to, but that depends on the nature of pain,
but as an initial assessment of the medicine's efficacy one pain category is enough.
Treatment :
- In the case of mild pain : a non-opioid mild analgesic like paracetamol is used plus
an adjuvant like caffeine or antihistamines.
Panadol extra contains caffeine ,although caffeine is mostly effective in case of
headaches than in the other types of pain. It is considered an adjuvant. Adjuvants
can also be antiemetics such as promethazine; which has antihistaminic and
antiemetic actions and reduces pain along with other agents.
-In the case of moderate pain, the patient is given weak opioids such as tramadol or
codeine with or without non-opioid analgesics like acetominaphen or NSAIDs and
with or without an adjuvant.
-In the case of severe pain , the patient is given a strong opioid, with or without nonopiods like acetominaphen or an NSAIDS , with or without an adjuvant.
IV opioids' efficacy is evaluated within 15 minutes, while in 1 hour for oral dosage
forms, then the dose is titrated, depending on the pain severity. If the pain wasn't
affected , the dose could be doubled.
In cases of severe pain like in cancer patients , the patient is usually given two forms
of the same drug; extended release and immediate release for pain breakthroughs,
to provide full coverage.
Note : In moderate to severe pain add on therapies including medications that treat
neuropathic pain could be included because in the severe nociceptic pain it is
possible to have a neuropathic component.
Regardless of the pain severity (mild, moderate, severe) or classification (acute,
chronic), the treatment should be scheduled around the clock (ATC), not PRN. Eg,
three times daily regardless of the symptoms severity as that prevents the
fluctuation in the pain signals which leads to variation refractoriness in the
responsiveness to the treatment.
Note : three times daily refers to administering the dose three times while the patient
is awake , ie , taking three doses from the time the patient wakes up till the time he
or she goes to bed , whereas Every 8 Hours strictly implies that a dose must be
taken every 8 hours regardless of sleeping patterns
Please note that there were many slides that weren’t covered in this lecture , this
sheet contains everything that the Doctor mentioned as well as some explanatory
texts taken from the slides to help making the mentioned points clear
Good luck