Facial Pain Flashcards
Which areas can pain be felt along the pain transmission pathway
- nociception
- peripheral nerve
- spinal modulation
- central appreciation
What fibres mediate nociceptive pain
a delta
c
Describe the nociception pathway
- Nociceptors detect noxious stimuli, they are peripheral cell nerve endings
- Noxious stimuli stimulates a action potential
- Afferent nerves (peripheral nerves) carry the action potential and relay the message to the central nerveous system (A-delta and C fibres)
- CNS relay cells carry the message through the spinal dorsal horn/spinal trigeminal nucleus - relay nerves can produce reflex for protection, bypassing the brain
- The message is carried via the CNS pathway - spinothalamic tract or anterior-tigeminothalamic tract
- It is then recieved by the forebain (thalamus)
How can peripheral nerves cause pain
- These are the nerves that carry the stimuli from the nociceptors to the central nervous system
- Damage to peripheral nerves can cause chronic pain
What is spinal modulation
This is the process of alterations in the pain signals along the transmission pathway of pain
It explains why individuals respond to the same stimuli differently
What forms from the first pharyngeal arch
Trigeminal nerve, muscles of mastication, malleus, incus, meckel’s cartilage
What forms from the second pharyngeal arch
Facial nerve, muscles of facial expression, hyoid
What forms from the third pharyngeal arch
Glossopharyngeal nerve, stylopharyngeus, common carotid artery, hyoid
What forms from the fourth and sixth pharyngeal arch
Vagus nerve, muscles of pharynx and larynx, aortic arch, laryngeal cartilages
What are the somatic nerves that supply the H&N
CN 5, 7, 9, 10 as well as C1, C2, C3
Can pain be transmitted through autonomic nerves
yes
What is referred pain
- Pain is felt in one part of the body but it originates from somewhere else
Why does referred pain happen
- Tends to be referred to areas of common embryological origin
- Referral is due to convergence of inputs into the CNS
- Both somatic and autonomic nerves can produce referred pa
Describe the peripheral nociception pathway
- Tissue damage causes production of substance P prostaglandins, 5-HT bradykinin which act on the nociceptor to produce an action potential that is transmitted through peripheral nerves and ends up as a signal in the spinal cord
What is the gatecontrol theory of pain
- Rubbing the skin where the pain is can disrupt the sensation of pain in a phenomenon referred to as gate control theory
- Rubbing the skin causes the A-beta fibres to transmit mechanical stimuli impulses and these fibres projection into the spinal cord, one of the branches activates an inhibitory interneuron
- The inhibitory interneuron causes the inhibition of secondary order pain projecting neuron and by inhibiting this, it stops the conduction of pain via the pain pathway
What is descending inhibition
Descending inhibition is where you allow function to continue despite pain input, the interneuron has been rendered less sensitive
What is descending facilitation
results in pain being felt more than normal - linked to pain expectation
What is neuronal plasticity
- Defined as the ability of neural networks in the brain to change through growth and reorganization
- It is when the brain is rewired to function in some way that differs to how it previously functioned
Describe how chronic pain results in neuronal plasticity
These patients will feel prolonged pain at sights which may have previously had injury but are now currently health
During the period of tissue damage, noxious stimuli and inflammation caused an elevation of nociceptive input from the periphery to the CNS
Prolonged nociception from the periphery then elicits a neuroplastic response at the cortical level to change its somatotopic organisation for the painful site, inducing pain sensitisation
Pain/central sensitisation is defined as an increased responsiveness of nociceptors in the CNS to either normal or sub-threshold afferent input
What type of pain does neuronal plasticity result in
This type of pain is called nociplastic pain, and is one of 3 pain mechanisms, the other 2 being known as neuropathic pain & nociceptive pain (i.e normal pain)
How do we manage these chronic pain px who are at risk of experiencing neuronal plasticity
- We want to try and prevent these changes by use of early pain management e.g LA or NSAID will reduce the likelihood of adaptations occuring
What are different ways of carrying out a pain assessment
- Physical symptoms can be assessed using PAIN scores (McGill)
- Emotional symptoms can be assessed using psychological scores (HAD)
- QoL scores can be useful too (OHIP)
What is chronic regional pain
- This is a problem that arises from the neuronal plasticity which produces nociplastic pain
How does chronic regional pain present
- Pain becomes delocalised, pain may be felt elsewhere
- Px may feel pain bilaterally
- May describe the pain as gripping, tight or a burning sensation
- They may also have a feeling of swelling and heat - likely linked to the vasomotor component. Vasodilation resulting from the pain signals, increasing blood flow to the tissues
- Colour changes may be seen in the skin
- Significantly disabling
What makes neuropathic pain different from nociceptive pain
Stimulus is generated beyond the nociceptor which remains unactivated
Somewhere between the brain & the nociceptor, there is damage and signals are being sent to the brain
What are examples of neuropathic pain
- post-herpetic neuralgia
- trigeminal neuralgia
- neuropathic lower back pain
How does zoster virus cause post-herpetic neuralgia
The virus inhabits the nerve and causes damage and the damage remains after the virus & its other symptoms e.g herpetic lesions are gone, resulting in this post-herpetic neuropathic pain
What is the presentation of neuropathic pain
Usually constant as nerve damage is there consistently
Usually at a fixed level as the nerve damage remains the same
Fixed location as the nerve supplies a location
Some evidence that some people have a genetic predisposition - their nerve ion channels do not heal properly after injury
What is the common injury with neuropathic pain
Usually accompanies a history of ‘injury’
‣ Facial trauma
‣ Extractions
‣ ‘Routine’ tx without complication
‣ Herpes zoster episode (shingles) - known as post-herpetic neuralgia
What can the treatments for neuropathic pain be divided into
- systemic medication
- topical medication
- physical
- psychological
What are examples of systemic medication that can be used to treat neuropathic pain
- pregabalin
- gabapentin
- tricyclic