Introduction to Pain pathology

1. Pain pathways and Pharmacotherapy
of pain management
Dr. S. Parasuraman,
Faculty of Pharmacy,
AIMST University.
Course: PHARMACOTHERAPEUTICS II

2. Pain pathways
• Pain has a biologically important protective function.
• Manifestations of pain related to tissue injury including
hyperalgesia, an exaggerated response to a noxious
stimulus, and allodynia, the perception of pain from
normally innocuous stimuli.
• Hyperalgesia and allodynia are the result of changes in
either the peripheral or central nervous systems and
causes peripheral or central sensitization, respectively.

3. Pain pathways
• The ascending pathways that mediate pain consist of
three different tracts:
– Neospinothalamic tract
– Paleospinothalamic tract
– Archispinothalamic tract

4. Pain pathways
• Neospinothalamic Tract

5. Pain pathways
• Paleospinothalamic Pathway

6. Pain pathways
• Paleospinothalamic Pathway

7. Pain pathways
• Archispinothalamic Pathway

8. Pain pathways
• Archispinothalamic Pathway

9. Sources of PainPain
Somatic Pain
Cutaneous, Superficial
or Peripheral Pain
Deep pain
Visceral Pain
Thalamic Pain
Psychosomatic Pain
Referred Pain
Phantom (illusory)
Pain
Reaction to Somatic
Pain
• Startle response
• Autonomic response
• Behavioral response

10. Sources of Pain
• Visceral Pain: In the
visceral organs,
nociceptors respond
to mechanical
stimulation such as
pressure, tissue
damage, and
chemical stimulation.

11. Sources of Pain
• Thalamic Pain: It also called as Dejerive-Roussy
syndrome. Stroke or occlusion in the
thalamogeniculate artery, which supplies the
lateroposterior half of the thalamus, can result in a
thalamic lesion, which is often accompanied by
neurologic conditions several months after the initial
event.
• Neuropathic Pain: It is a sharp, shooting and
devastating pain.
• Psychosomatic Pain: Psychic reaction to pain includes
all the well-known responses to pain such as anguish,
anxiety, crying, depression, nausea and excess
muscular excitability through the body.

12. Sources of Pain
• Referred Pain: is a painful sensation at a site other
than the injured one. The pain is not localized to the
site of its cause (visceral organ) but instead is localized
to a distant site.

13. Sources of Pain
• Phantom (illusory) Pain: It is the experience of pain
without any signals from nociceptors.

14. Pathological classification of pain
• Nociceptive: represents the normal response to
noxious injury of tissues.
• Neuropathic: Pain initiated or caused by a primary
lesion in the somatosensory nervous system.
• Inflammatory: Activation and sensitization of the
nociceptive pain pathway by a variety of mediators
released at a site of tissue inflammation.

15. Time course: Pain duration
• Acute pain (less than 3 to 6 months duration): Pain
arises from activation of nociceptors for a limited time
and is not associated with significant tissue damage
(e.g., a pin prick).
• Chronic pain (more than 3-6 months): It is prolonged
pain lasting for months or longer that arises from
tissue injury, inflammation, nerve damage, tumor
growth, lesion or occlusion of blood vessels.
• Fibromyalgia: It is characterized by widespread chronic
pain throughout the body, including fatigue, anxiety
and depression.

16. Overview of inflammatory processes
• Inflammation begins when a stimulus, such as infection,
physical stress, or chemical stress, produces cellular
damage.

17. Overview of inflammatory processes
• The more important inflammatory mediators are the
eicosanoids, biological oxidants, cytokines, adhesion
factors, and digestive enzymes (proteases, hyaluronidase,
collagenase, and elastase).
• EICOSANOIDS: The pathway initiated by cyclooxygenase
(COX) produces prostaglandins; the lipoxygenase pathway
generates leukotrienes.

18. Overview of inflammatory processes
• Biological effects of eicosanoids

19. Overview of inflammatory processes
• Biological Oxidants: The biologically derived oxidants are
potent bacterial killers but are also a major contributing
factor in tissue injury that results from the inflammatory
response. These oxidants include the superoxide anion
(∙O2-), hydrogen peroxide (H2O2), nitric oxide (∙NO),
peroxynitrite (∙OONO∙), hypochlorous acid (HOCl),
peroxidase-generated oxidants of undefined character,
probably the hydroxyl radical (∙OH), and possibly singlet
oxygen (1O2).
• Cytokines: Tumor necrosis factor-α (TNF- α) and
interleukin 1(IL-1) are produced primarily by cells of
the monocyte–macrophage lineage.

20. Pharmacotherapy of acute pain
• SORT (The Strength-of-Recommendation Taxonomy):
key recommendations for practice
Read more:
Blondell RD, Azadfard M,
Wisniewski AM.
Pharmacologic therapy for
acute pain. Am Fam
Physician. 2013;87:766-72.

21. Pharmacotherapy of chronic pain
• Treatment algorithm for pharmacotherapy of chronic
non-cancer pain
Read more:
Lynch ME, Watson CP. The
pharmacotherapy of chronic
pain: a review. Pain Res Manag.
2006 ;11(1):11-38.

22. Thank you