PAIN MODULATION

Prof. Ashraf Husain

MODULATION

• Pain modulation means pain perception variability which is influenced by endogenous and exogenous mechanism

3

5

Referral of pain from the internal organs

• Meninges Back of head and neck• Heart Central chest arms

(usually left), neck, occasionally abdomen.

• Trachea Behind sternum• Diaphragm Shoulder tip• Oesophagus Behind sternum

Cont…

Organ Site of reffered pain

6

• Stomach, duodenum Upper abdomen, epigastrium

• Small bowel, pancreas Around umbilicus• Large bowel, bladder Lower abdomen

above pubic bone

Organ Site of reffered pain

7

VISCERAL PAIN

8

VISCERAL PAIN PATHWAY

Pain - Aδ and fibersTravel with autonomic afferent

Spinal cord(Dorsal Horn)

Lat. spinothalamic tract

Thalamus

Somatosensory Cortex

9

• Poorly localized• Associated with nausea and autonomic disturbance• Often referred to another part of the body• Cutting, crushing are not painful when applied to viscera• Pain is caused by distension, ischemia and inflammation

CHARACTERSITICS OF VISCERAL PAIN

MODULATION

• Pain modulation means pain perception variability which is influenced by endogenous and exogenous mechanism

10

• Pain modulation can be discussed under following headings– Spinal modulation of pain input

• Gate theory of pain

– Supra spinal modulation• Role of periaqueductal grey (PAG) matter• Role of Nucleus Raphe Magnus (NRM)

– Pain modulation by use of Opioid neurotransmitters eg: endorphin, enkaphalin Dynorphin.

11

12

A MODAL OF “GATING” OF PAIN

SPINAL MODULATION

13DORSAL HORN GATING MECHANISM

SPINAL MODULATION

14

ASCENDING AND DESCENDING PAIN PATHWAYS

15

Descending AnalgesicPathway

SUPRASPINAL MODULATION

SU

PR

AS

PIN

AL

MO

DU

LA

TIO

N

17

Neurotransmitters in AnalgesicPathway

OPIOID RECEPTOR MODULATION

18

MECHANISM OF OPIOID NEUROTRANSMITTER ACTION:•ENDORPHIN:

•Neurons using endorphin or enkaphalin are found in PAG where they inhibit GABAnergic interneurons that normally suppress the anti-nociceptor neurons

•ENKAPHALIN:•It is used by interneurons in lamina II responsible for inhibiting the lamina – I nocioceptor-specific spinothalamic neurons

•ENDOGENOUS MORPHIN:•It has been identified in terminals forming synapses with neuron having μ-opioid receptors in pain modulating pathways.

Chronic Pain

• Chronic pain can be considered as bad

pain because it persist long after injury

and is often refractory to pain killers.

• Chronic pain caused by nerve injury is

called neuropathic pain.

19

Neuropathic pain

• Caused by the damage to peripheral nerve ( adrenalin release by sympathetic discharge)

• The distal cut end develops a scar tissue forming rounded ball ( neuroma) which is sensitive to pressure.

• Repeated activation causes continuous pain.• Examples are like, post herpetic neuralgia

and diabetic neuropathy.

20

Phantom pain

• Pain felt in an amputated part long after amputation was done.

• Many explanations are given to explain this phenomenon.

21

Stress induced analgesia

• It’s a well known phenomenon seen when the soldier is wounded in battle field but feels no pain until the battle is over. The cause is not known may be it is similar to Gate control hypothesis.

22

23

• Hyperalgesia: Excessive Pain• Allodynia: Pain caused by any other sensation

e.g. touch will cause pain.• Muscular Pain: Less blood flow in the muscles

(ischemia).• Stress analgesia: Mild degree of pain is not felt if

the other part of the body has excessive pain.• Causalgia: Burning pain.

TERMS FREQUENTLY USED

24

Thalamic Syndrome.Obstruction of the thalmogeniculate branch of the posterior cerebral artery Affects posterior thalamic nuclei.. Prolonged severe pain.

TERMS FREQUENTLY USED

25

TRIGEMINAL NEURALGIA•It is excruciating intermittent pain by stimulation of trigger area in the face as for eg. Washing of face, combing hair, blast of air on face.•It results from compression of trigeminal nerve root by blood vessels

TERMS FREQUENTLY USED

26

SITES & MECHANISM OF PAIN RELIEF

27

Trans Coetaneous Electrical Nerve Stimulation

(TENS)

28