WHY DOES ENDOMETRIOSIS CAUSE SO MUCH PAIN? Dr Michael W Platt MA MB BS FRCA Lead Clinician in Pain...

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WHY DOES ENDOMETRIOSIS CAUSE SO MUCH PAIN?

Dr Michael W Platt MA MB BS FRCALead Clinician in Pain Medicine, Consultant in Anaesthetics,

Honorary Senior Lecturer, Faculty of Medicine, Imperial College London,

Department of Anaesthetics St Mary's Hospital, Imperial College Healthcare NHS Trust

Praed Street, London W2 1NY

2007 Dr Michael W PlattImperial College

• The pain associated with Endometriosis is the most difficult symptom to cope with for most women. For many, the pain they suffer severely interferes with every day life. It can be constant or it can be cyclical and coincide with a woman’s period.

What is pain?

• Emotional

• Sensory

• Acute or Chronic

• Totally subjective

• Can be described qualitatively

• Can be graded quantitatively

What is pain?

• Can be graded quantitatively:

Why do we have pain?

• Recognition of self

• Protection from trauma

• Reduction of trauma

• Warning sign of illness

• Warning sign of infection

What happens when pain is absent?

• Congenital insensitivity to pain

• Sensory nerve damage secondary to disease– Diabetes– Stroke– Trauma– Syphilis– Leprosy

• Acute (physiological) Pain:– An unpleasant sensory and emotional

experience associated with actual or potential tissue damage.

• Chronic (pathological, intractible) Pain:– Pain in the absence of, or persisting following

the removal of, a noxious stimulus.

• Acute: Post-trauma, surgery etc.

• Chronic:– Neuropathic pain– Mechanical pain– Chronic inflammation– Complex regional pain syndrome

• Cancer pain

Complicated neurobiology of pain

• Not a simple ‘hard-wired’ system.

• Long-term changes occur in the PNS and CNS following a noxious stimulus.

• This ‘plasticity’ changes the body’s response to further stimuli

Pain Pathways

• Nociceptor

• Axon

• Dorsal Root Ganglion

• Dorsal Root

• Internuncial neurones

• Cross-over to opposite side

• Thalamus and Cortex

Peripheral sensitisation

• Inflammatory response:Release of mediators from mast cells etc:– Substance P– neurokinin A– calcitonin gene-related peptide– lead to further release of ‘inflammatory soup’:

• K, 5-HT, bradykinin, histamine etc

• Act to sensitise high-threshold receptors

‘Neuropathic pain’

• Burning, sharp, stabbing sensations

• eg diabetic neuropathy, post-amputation pain etc.

• Treatment of peripheral neuropathic pain include tricyclic antidepressants, anti-convulsants, clonidine, opioids, local anaesthetics and anti-arrhythmic agents.

Sympathetic nervous system

• Important role in generation and maintenance of chronic pain states.

• ‘Complex regional pain syndromes:– Sympathetic dysfunction:

• vasomotor & sudomotor changes

• abnormal hair & nail growth

• osteoporosis

• sensory symptoms: burning, hyperalgesis, allodynia

Gate Theory of Pain

Central sensitisation

• Changes that occur in the dorsal horn in response to an injury, following barrage of stimuli into the horn.

• Phenomenon of ‘wind-up’ involving the NMDA receptor, making neurons more sensitive - ie sensitising them.

• Expansion in receptive field size.

Ascending tracts

• 2nd order neurons ascend in spinothalamic, spinoreticular and spinomesencephalic tracts.

• Terminate in structures throughout the brain stem, thalamus, and cortex.

• Thalamus has 2 main groups of relays:– sensory discriminative aspects– affective-motivational aspects

Descending modulation

• descending inhibitory modulation from:– hypothalamus– PAG– locus coeruleus– nucleus raphe magnus– etc

• Involves opioids, 5-HT, n-adr, GABA

Visceral Pain

• There are specific nociceptors originating in viscera.

• They respond to:– tension (contraction)– chemical nociception– sensitisation of nociceptors– effects of ischaemia

Concept of referred pain

• Visceral nociceptors rarely activated

• Much more common to activate somatic nociceptors

• Spinal cord and brain interpret visceral signals as emanating from somatic source

• Convergence of visceral and somatic afferents may account for this

Diagnosis of Pain in Endometriosis

• Acute, cyclical pain – due to pressure, chemical irritation, nerve compression

• Chronic, non-cyclical pain – due to neuropathic pain, sources outside the pelvis (back, groin, etc.)

• Other visceral pain – especially bladder pain.

Measurement of Pain

• Visual Analogue Score– make as objective as possible– Straight line 10 cm long– No other markings

• Personality inventories– Help to score chronic pain in terms of

personality type and stress markers.

Treatment of Pain in Endometriosis

• Acute Pain:– NSAIDS– Hormonal – Oral Contraceptive– Systemic analgesia, opioids– Other techniques (TENS, Acupuncture)

Pain Ladder

• Minor pain: paracetamol, aspirin

• Moderate pain:– combination with minor opioids

• Co-proxamol (propoxifine), Co-dydramol (codeine)

– Minor opioids alone - eg Pethidine, Tramadol

• Severe pain:– Opioids: Morphine etc.

Endometriosis and Inflammatory Pain: Use of NSAIDS

• Cyclo-oxygenase pathway blocked– 2 forms:

• COX1 & COX2

• COX1 always present

• COX2 only induced by inflammation

• Also have central role, where both COX1 & COX2 are found as neuro-transmitters

NSAIDS

• COX 2 antagonists preferable where there is high-risk of peptic ulceration / bleeding

• Still not 100% guarantee.

Treatment of Pain in Endometriosis

• Chronic / Intractable Pain:– Multiple modality pain clinic - holistic

approach– Drugs– Nerve blocks– TENS, Acupuncture– Physio, occupational Ther., Psychology

Neuropathic Pain in Endometriosis

• Not responsive to opioids

• Two main classes of drugs used:– Tricyclic antidepressants (esp Amitriptyline)– Anti-epileptics:

• Carbamazepine

• Sodium valproate

• Clonazepam

• Gabapentin (Pregaballin)

Gracilis Adductor longus

Adductormagnus

Adductorbrevis

Obturatorexternus

Obturatorinternus

Other complicating factors

• Psychosocial & spiritual processes strongly influence the impact and expression of pain.

• (Saunders 1985, Portenoy 1992; Breitbart 1994)

Some factors:

• Pain interrelated with:

– depression (r = 0.33 with pain)– lack of family support (r = -0.15 with pain)– desire for death (r = 0.47 with depression)

Some correlates with severe pain:• Patient anxiety: r = 0.30

• Communication problems: r = 0.29

• Constipation: r = 0.24

• Poor co-ordination: r = 0.21

• Family anxiety: r = 0.19

• Nausea: r = 0.19

• Vomiting: r = 0.13

• Other symptoms: r = 0.11

Factors that diminishquality of life:

PainOther symptomsPsychological

distressSpiritual/existential

distressFamily distressSocial distressFinancial needsHealth care concerns (eg poor communication)

Perception &appraisal ofpain

Expressionof suffering

A MODEL OF SUFFERING

Summary

• The pain system is a very complex one.

• Endometrial Pain may be difficult to treat due to a variety of causes, and these should be addressed in the management of the patient:

• Adequate pain assessment, including those factors which are inter-related is essential.

WHY DOES ENDOMETRIOSIS CAUSE SO MUCH PAIN? Dr Michael W Platt MA MB BS FRCA Lead Clinician in Pain...

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