Sympathetic nervous system & pain

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Sympathetic nervous system & pain

Author: Himanshu Marathe

sympathetic nervous system & painDefinition of Autonomic nervous system- It is defined as neurological substrate that acts to maintain homeostasis in the body1. So basically it is a complex set of neurons which help in mediation of internal homeostasis without conscious intervention or voluntary control. It is different than somatic nervous system in many ways.

It has two types–

  • sympathetic nervous system & painSympathetic
  • sympathetic nervous system & painParasympathetic

Sympathetic system is generally acted as a reaction which is called flight or fight reaction.

Sympathetic fibres arise arise from thoracolumbar region of spinal cord i.e T1-L2 level. Sympathetic supply consists of preganglionic and post ganglionic fibres with preganglionic fibres having cell bodies in lateral horn. The anatomy and distribution of sympathetic nerves and their supply is shown in figure below.

sympathetic nerves and pain

The sympathetic nerves pass along the somatic nerves in common path. Efferent fibres start from lateral horn. Just after coming out of neural foramen, they pass through myelinated white rami communicants and join sympathetic trunk on anterolateral part of vertebral body. Some fibres synapse with post ganglionic fibres at ganglions near to vertebral column and some near to viscera. There is a concept of anatomical convergence and diversion with sympathetic system. It means that many preganglionic fibres can go to one post ganglionic fibre and reverse. The afferent fibres travel along the somatic nerves and blood vessels and enter sympathetic chain via grey rami communicants and leave via white rami communicants and join mixed spinal nerve4.

Normally sympathetic system does not cause pain. But in certain conditions sympathetic nerves can carry painful sensations.

Causes of pain because of sympathetic nerves–

sympathetic nervous system & painSomatic sympathetic coupling.

It can be seen at –

  • sympathetic nervous system & painDorsal root ganglion
  • sympathetic nervous system & painPeripheral nerve
  • sympathetic nervous system & painReceptor level

sympathetic nervous system & painIDD– Pathophysiology of IDD is the sensitisation of sympathetic system at outer one third of annulus fibrosus.

sympathetic nervous system & painCompression near foramen- After coming out of neural foramen, somatic and sympathetic fibres go in same path. Compression and damage at this site can cause sympathetic pain also.

sympathetic nervous system & painSympathetically mediated neuropathic pain– If a somatic nerve gets damaged, it can lead to short circuits between damaged fibres and sympathetic system. So during activation of sympathetic system like stress, painful stimuli are carried via afferents of somatic nerves.

Type of pain– As seen in anatomy,sympathetically mediated pain will not have dermatomal distribution. So it will be a vague and non localised type of pain.

Modulation– It is said that sympathetic ganglia contain interneurons which have modulatory functions.

Sympathetic blockade and its significance in pain management5 – Sympathetic blockade causes interruption in transmission by both efferent and afferent fibres. It does not result in sensory and motor loss as seen in somatic blockade.

Examples of sympathetic blockade at various levels:

  • sympathetic nervous system & painStellate ganglion block and lumbar sympathetic block used for CRPS of upper and lower limbs.sympathetic nervous system & pain
  • sympathetic nervous system & painSplanchnic nerve block for malignant or benign upper abdominal pain
  • sympathetic nervous system & painSphenopalatine ganglion block for headache and facial pain
  • sympathetic nervous system & painCeliac plexus block for upper abdominal malignancy and chronic benign pain.
  • sympathetic nervous system & painT2-T3 Sympathetic block for upper limb CRPS and some types of thoracic pain.
  • sympathetic nervous system & painSuperior & inferior hypogastric plexus block can be used in cancer and non cancer chronic pelvic pain.
  • sympathetic nervous system & painGanglion impar block is used to alleviate pain arising from perineal region.
  • sympathetic nervous system & painEpidural drug administration lead to leaking of drug through neural foramen and bathing of sympathetic fibres hereby blocking sympathetic system.

 

Referrences- 1) Das G. Basics of pain management. CBS Publishers and distributors. New Delhi: 2017.p.5

2)  Ebneshahidi D. (Internet). Mymission.lamission.edu.2017 (cited 7 July 2018). 5

3) Ebneshahidi D. (Internet). Mymission.lamission.edu.2017 (cited 7 July 2018). 11

4) Das G. Basics of pain management. CBS Publishers and distributors. New Delhi: 2017.p.6-7

5) Das G. Basics of pain management. CBS Publishers and distributors. New Delhi: 2017.p.7-8