CASE 2 - pain, sciatica etc Flashcards
antidromic and orthodromic stimulation?
stimulation of nociceptive C fiber results in both orthodromic conduction to the spinal cord and antidromic conduction to other axon branches, i.e., the axon reflex which can stimulate the release of peptides, such as substance P and calcitonin gene-related peptide, resulting in vasodilation and increased permeability
what is the most common type of radiculopathy?
lumbar radiculopathy
what are the most common causes of radiculopathy?
- herniated disc (compression by displayed iv disc)
- degenerative disc disease
- spondylosis
what are the most common sites of herniated disc?
C5/C6 in neck and L5/S1 in lower back
what is an acute disc herniation?
herniation of the nucleus pulposus through a rupture in the annulus fibrosis
what is a pure hernia?
the nucleus pulposis protrudes from the iv disc
what is degenerative disc disease?
vertebra becomes deformed as a result of the ageing process, causing a narrowing in or around the spinal canal
what is spondylosis?
discs initially dehydrate, thus losing height and the disc annulus prolapses
what is sciatica?
refers to the nerve pain in the back when the sciatic nerve is affected — results in radiating pain to the leg. this nerve pain is often caused by a back hernia
what does radiculopathy present with?
pain, weakness, reflex changes and sensory loss
what are some signs and symptoms of radiculopathy?
- in disc prolapse, pain may be acute and related to physical exertion
- pain in lower back
- pain radiates to the leg over the course of the nerve (sciatica)
- sensory loss or altered sensation in the distribution of the affected nerve root
- irritation, loss of sensation or a numb or cold sensation in the leg
- loss of strength or disrupted reflexes
- the radiating pain can be sharp and run down to below the knee, over the lower leg and even to the foot
- stretching the nerve makes symptoms worse (straight leg raise test) = sciatic stretch (implies L5 or S1 lesion)
how is radiculopathy diagnosed?
- review of medical history and symptoms
- straight leg raise test if lumbar radiculopathy assumed
- MRI or CT scan — identify the cause and location of radiculopathy
- electromyography — can be used to rule out other diseases that cause nerve damage
what can MRI be useful to rule out?
cauda equina syndrome
what is cauda equina syndrome?
= caused by a compression of the nerve roots forming the cauda equina
- it is a surgical emergency to prevent permanent neurological defects
- can be caused by lumbar disc herniation (may be secondary to degenerative disc disease, trauma or infection), spinal vertebral fractures, infection, malignancy
how is radiculopathy treated?
- NSAIDs eg. aspirin, ibuprofen, naproxen
- physical therapy to reduce pain, improve posture, and strengthen muscles
- steroid injections if pain persists, to reduce inflammation specifically in the area affected
- other medications, such as oral steroids, stronger pain medications, or the anti-seizure medications gabapentin, may also be prescribed
- spinal nerve decompression surgeries are sometimes needed
what spinal decompression surgeries are available?
- microdisectomy : most common surgery for herniated discs. herniation is found and the herniated piece is removed
- laminectomy : aim is to relieve pressure on the spinal nerve
- spinal fusion surgery : rare treatment. used to treat spinal segments that are unstable or collapsed. a vertebral bone is attached or “fused” to an adjacent vertebral bone so that they
grow together into one long bone. the immobility caused stops the spinal instability that was causing the pain
what are dermatomes?
- sensory nerve fibres that innervate a segment of skin
- an area of skin that is mainly supplied by a single spinal nerve
each dermatome is associated with what?
a single spinal nerve
how many dermatomes are there and why?
30 = 1 less than the number of spinal nerves — start at C2 because C1 typically doesn’t have a sensory root
why are dermatomes important?
- because they can help to assess and diagnose a variety of conditions
- symptoms that occur along a specific dermatome may indicate a problem with a specific nerve root in the spine
eg. radiculopathies — refers to conditions in which a nerve root in the spine is compressed or pinched. symptoms can include pain, weakness and tingling sensations. pain from radiculopathies can follow one or more dermatomes. one form of radiculopathy is sciatica.
origin of sciatic nerve?
L4-S3
describe the course of the sciatic nerve
- enters the gluteal region through the greater sciatic foramen, beneath the piriformis muscle
- descends over the lateral hip rotators
- passes through the posterior compartment of the thigh to reach the superior border of the popliteal fossa
what does the sciatic nerve branch into?
muscular branches and the tibial and common fibular nerve
what does the sciatic nerve supply?
- motor innervation to the posterior compartment of the thigh via muscular branches
- motor innervation to the posterior compartment of the leg via the tibial nerve
- motor innervation to the muscles of the anterior and lateral compartments of the leg via the common fibular nerve
- sensory innervation to the skin of the leg and root via the common fibular and tibial nerves
label
what can acute overdose of paracetamol lead to?
fatal liver damage
inhibition of ____ causes the unwanted side effects of ibuprofen
COX1
ibuprofen reduces prostaglandin synthesis via what pathway?
arachidonic acid pathway
describe gabapentin
- gabapentinoid
- anticonvulsant
- binds to a2d part of Ca channel — decreases subsequent release of excitatory neurotransmitters
- dizziness, sleepiness, water retention difficulty walking, upset stomach
describe pregabalin
- gabapentinoid
- anticonvulsant
- binds to a2d subunit of voltage-gated Ca channels, modulating the release of several excitatory neurotransmitters such as glutamate, substance P, NE and CGRP
describe amitriptyline
- tricyclic antidepressant
- inhibits the membrane pump mechanism responsible for the reuptake of transmitter amines such as NE and serotonin, thereby increasing their conc at the synaptic clefts of the brain
- dry mouth, constipation, dizziness, sleepiness, headache, difficulty peeing
describe co-codamol
- compound analgesic —> paracetamol + codeine phosphate
- codeine is an opioid analgesic used to treat moderate to severe pain
- selective for the mu opioid receptor
- opioids reduce pain signal transmission by activating pre-synaptic opioid receptors — leads to reduced intracellular cAMP conc, decreased Ca++ influx and thus inhibits the release of several neurotransmitters such as glutamate and substance P
why is chronic pain hard for GPs?
- professional uncertainty
- reluctant to up doses — addiciton
- emotional burden
- unable to help
what is a spinal cord stimulator and what is spinal cord stimulation?
= an implanted device that sends low levels of electricity directly into the spinal cord to relieve pain
- electrodes placed between the spinal cord and vertebrae (epidural space), and the generator is placed under the skin, usually near the buttocks or abdomen
- the stimulators allow patients to send the electrical impulses using a remote control when they feel pain
how does transcutaneous electrical nerve stimulation (TENS) work?
- electrodes are used to activate large-diameter afferent fibres that overlap the area of injury and pain
- stimulation of the dorsal columns via surface electrodes presumably relieves pain because it activates large numbers of AB fibres synchronously
- TENS machines are thought to work in 2 ways:
1. a high pulse rate triggers the ‘pain gate’ to close
2. a low pulse rate stimulates the body to make its own
endorphins
withdrawal is only in patients who have developed what?
a drug tolerance
how is scanning used in pain management?
used to confirm diagnosis
MRI vs CT in pain management
MRI
- normally used
- not used in an emergency
- slow, expensive, bit more effort, no radiation, high quality
CT
- used in emergency
- quick, cheap, convenient, involves radiation, poor quality
what is biographical distribution? chronic illness?
used to describe the experience of chronic illness and the way in which a life-threatening illness breaks an individual’s social and cultural experience by threatening his pr her self-identity
- chronic illness can affect the patient’s role in the family and his or her relationship with family members
- also impacts their daily life and relationship with their friends, colleagues and the community
what are the 4 phases of pain pathways?
- transduction
- transmission
- modulation
- central perception
what are the mechanisms of endogenous opioid peptides in the descending inhibitory pathways?
- activation of mu, kappa, and delta opioid receptors — decreased presynaptic Ca++ influx — decreased release of glutamate and SP
- increased K+ conductance in dorsal horn neurons
what type of fibre is the afferent axon with the largest diameter?
Ab fibres
what are A gamma fibres?
motor neurons that control the intrinsic activation of the muscle spindle
what are the 3 main neurotransmitters released by primary afferents?
glutamate, SP and CGRP
where do 2nd order neurons cross the midline?
at the white anterior commissure
where do 2nd order neurons go after crossing the midline?
ascend to the thalamus via the contralateral spinothalamic tract, carrying both pain and temperature sensations
from the thalamus, where is the stimulus sent?
- to the somatosensory cerebral cortex via fibres in the posterior limb of the internal capsule
- other thalamic neurons project to areas of the cortex associated with emotional responses (eg. cingulate gyrus, insular cortex)
what type of neurons are the 1st order neurons in pain pathways?
pseudounipolar
what type of fibres are responsible for dull, deep and throbbing type pain?
C fibres — unmyelinated and slow conducting speed, have large receptive fields (therefore poor localisation of pain)
where do C fibres mainly terminate and what do they release?
- Rexed laminae II (AKA substantia gelatinosa)
- release substance P
what fibres are mainly responsible for localised sharp pain?
alpha delta (Ad) fibres
central sensitisation
thought to arise from an increase in the number of NMDA receptors, as well as increased sensitivity of NMDA receptors to glutamate. These changes occur on the dendrites of second-order neurones and are a result of prolonged glutamate release from first-order neurones ( due to persistent nociceptor activation).
what are the 3 types of endogenous opioids and what do they bind to?
- B-endorphins — predominantly bind to mu opioid receptors
- Dynorphins — predominantly bind to opioid kappa receptors
- enkephalins — predominantly bind to delta opioid receptors
what are silent nociceptors?
receptors that are normally unresponsive to noxious mechanical stimulation, but become stimulated during inflammation
which of the following is a substance that would NOT stimulate a receptor?
- substance P
- ACh
- peptide T
- serotonin
- K+
peptide T
what type of nerve fibre is responsible for deep, unspecific pain?
C fibres
chillies taste hot because capcaisin activates whicg type of nerve fibre?
A beta
what is the spinocerebellar tract responsible for?
proprioception
what is the spinoreticular tract responsible for?
emotional and arousal aspects of pain
according to the gate control theory, unwanted pain can be reduced by stimulating whcih type of nerve fibre?
A alpha
herniation of a spinal disc is most likely to occur on what side?
posterior
which age group is at greatest risk for spinal disc herniation?
30-50
