Somatosensory Pathology

Question 1

2 tests of THE INTEGRITY OF THE ASCENDING SOMATOSENSORY PATHWAYS

Answer 1

• Quantitative sensory testing (QST)

- Electrical perceptual thresholds (EPT)-

Question 2

What is an Electrical perceptual thresholds (EPT) test

Answer 2

like QST but semi-automated Electrical current sent to skin and the patient either feels it or doesn’t

Question 3

What is a Quantitative sensory testing (QST) test

Answer 3

a set of various tools we can use to look into the integrity of all of the different modalities e.g. using a brush to stroke someone’s arm 13 different tests can be done

Question 4

what causes nociceptive pain?

Answer 4

Tissue damage, typically acute e.g. skin cut

Question 5

what causes muscle pain?

Answer 5

Lactic acidosis, ischaemia e.g. stretching, fibromyalgia)

Question 6

what causes somatic pain?

Answer 6

Well-localised e.g. inflammation, infection

Question 7

what causes visceral pain?

Answer 7

Deep, poorly localised e.g. stomach, colon, IBS

Question 8

what causes referred pain?

Answer 8

From an internal organ/structure e.g. angina

Question 9

what causes neuropathic pain?

Answer 9

PAIN CAUSED BY A LESION OR DISEASE OF THE SOMATOSENSORY NERVOUS SYSTEM

Question 10

How does ACUTE AND CHRONIC PAIN manifest

Answer 10

hyperalgesia and allodynia

Question 11

What comorbidities can you get with acute and chronic pain

Answer 11

anxiety and depression as secondary comorbidities

Question 12

What does neuropathic pain feel like

Answer 12

Sharp, burning, electric shocks

Question 13

Success of analgesic opiated in neuropathic pain?

Answer 13

Poor

Question 14

3 types of neuropathic pain?

Answer 14

 Sciatica (most common)- spinal nerves compressed in intervertebral foramen
Diabetic neuropathy
 Post-hepatic neuralgia can be caused by shingles
HIV induced neuropathy
 CRPS = pain around the whole body that spreads spontaneously

Question 15

What types of neuropathic pain can you get (5)

Answer 15

ALLODYNIA
Hyperalgesia
Sensitisation
Hypoalgesia
Paraesthesia

Question 16

What is ALLODYNIA

Answer 16

Pain due to a stimulus that does not normally provoke pain e.g. brush

Question 17

What is Hyperalgesia

Answer 17

Increased pain from a stimulus that normally provokes pain

Question 18

What is Sensitisation

Answer 18

Increased responsiveness of nociceptive neurons to their normal input

Question 19

What is Hypoalgesia

Answer 19

Diminished pain in response to a normally painful stimulus

Question 20

What is Paraesthesia

Answer 20

Abnormal sensation, whether spontaneous or provoked

Question 21

How do we diagnose and asses neuropathic pain (2)

Answer 21

Clinically we use a combination of questionnaires and simple sensory tests e.g. brushing etc.

Question 22

What is central sensitization in chronic pain

Answer 22

Increased amount of pain was found not to just be from sensitization in the periphery but in the spinal cord

Question 23

What do NMDA receptors do and how does result in central sensitisation and chronic pain

Answer 23

(mechanism for central hypersensitisation) they allow a big post-synaptic depolarisation which allows calcium into the neuron- this activates intracellular signalling and increases synaptic strength and our sensitivity

Persistent activation of NMDA receptor can result in development of chronic pain

Question 24

What happens in hyperalgesia

Answer 24

Central sensitisation via persistent NMDA activation which causes a lack of inhibitor from interneurons

Question 25

What happens in allodynia

Answer 25

Almost a rewiring of neurons so mechanoreceptors can stimulate nociceptive fibres

Question 26

What sort of shape is curve of a stimulus intensity against pain intensity graph

Answer 26

sigmoidal

Question 27

What is descending modulation of chronic pain

Answer 27

Monoamines released from the brainstem that work to inhibit spinal cord excitability (and thus reduce pain)

Question 28

What are 2 methods of descending modulation of pain

Answer 28

THE PAG-RVM AXIS
LOCUS CERELEUS (LC):

Question 29

The LOCUS CERELEUS (LC) in descending pain modulation (location, NT,

Answer 29

This is in the pons

This uses noradrenaline as its main neurotransmitter

Question 30

The PAG-RVM AXIS in descending pain modulation (names of nuclei, locations, NT)

Answer 30

Periaqueductal gray - midbrain
rostral ventral medial medulla - Pons
serotonin (5-HT)

Question 31

• The PAG and RVM contain high concentrations of X RECEPTORS

Answer 31

Mew opioid

Question 32

How does the PAG-RVM axis inhibit pain

Answer 32

• The PAG and RVM contain high concentrations of  OPIOID RECEPTORS
• Endogenous opioids enhance descending inhibition from the PAG-RVM axis
• Reduce pain transmission from the dorsal horn by inhibiting glutamate release i.e. activation of spinothalamic neurons
• Forms part of an ENDOGENOUS ANALGESIC SYSTEM

Question 33

Drugs used to target descending pain modulation?

Answer 33

• Opioids
• Antidepressants (Tri-cyclic Antidepressants (TCAs), Serotonin Noradrenaline Reuptake Inhibitors (SNRIs) and Selective Serotonin Reuptake Inhibitors (SSRIs)

Question 34

Effectiveness of SSRIs as analgesics?

Answer 34

low analgesic efficacy

Question 35

Effectiveness of SNRI as analgesics?

Answer 35

Effective

Question 36

MoA of SNRIs in pain inhibition?

Answer 36

• If you give an SNRI e.g. duloxetine, it binds to the presynaptic or postsynaptic terminal in the dorsal horn and inhibits NA reuptake from the synaptic cleft
• This means NA acts on inhibitory 2 receptors for longer and inhibitory influence is increased (pain is reduced)

Question 37

3 neuropathic pain patient clusters?

Answer 37

1. SENSORY LOSS
2. THERMAL HYPERALGESIA
3. MECHANICAL HYPERALGESIA