Anatomy and Physiology of PainDr. Gautam Das MD, FIPPChairman, Indian chapter of World Institute of Pain

Pain management: What is new?Newer developments in understanding the pathophysiology of pain.Newer concepts of analgesic therapy.Newer drugs to manage pain.Interventional Pain Management to diagnose & treat pain.

Definition of PAINPain is "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage" ( IASP : 1979).

Many people report pain in the absence of tissue damage or any likely patho-physiological cause. If they regard their experience as painit should be accepted as pain. (IASP)

Example of Phantom limb painThey have pain in the limb which is not there.If the pain is always associated with actual or potential tissue damage then they should not feel pain on the limb where there is no tissue at all !So till 1960s they were send to psychiatrist thinking they must be mad because they are complaining pain on limb which is not there!Now it is a well established phenomenon with clear pathophysiological explanation.

So in Phantom Limb Pain & other Chronic Pain, problems lies in the nerves not in the damaged tissue.

Types of Pain

Types of PainAcute Pain /Physiological PainNociceptiveSymptom of a diseaseTreatment of diseases cures pain & it is self-limiting.

Chronic Pain /Pathological PainNeuropathic A disease itself, a disease of nervous system.Difficult to treat & sustaining.

Types of PainAcute Pain /Physiological PainSimple relationship between pain and tissue damageProportionate to the clinical findingBiological function & our friendChronic Pain /Pathological PainDissociated relationship between pain and tissue damageDisproportionate to the clinical findingNo Biological function

PAIN: an alarm?

True for Acute Pain which is our friend. Chronic Pain is a false alarm, it is a disease itself.

What is Chronic Pain?American chronic pain association defines it as Pain that continues a month or more beyond the usual recovery period.Some has described chronic pain as pain persisting more than 3 month as by three months pain itself becomes a disease. All pain is acute pain till it becomes chronic pain.

Chronic PainWith ongoing tissue damageWithout ongoing tissue damageCentral Sensitization is a constant feature

Acute PainChronic Pain without tissue damagePain

Chronic Pain with tissue damage

Pathogenesis of Chronic PAIN

Sensitization Sensitization is a phenomenon of inappropriate or disproportionate response to normal stimulus Peripheral SensitizationCentral Sensitization

Peripheral sensitization

Peripheral sensitization Sensitization of primary afferent terminals.Active nociceptors become sensitized and sleeping nociceptors awaken. Damaged axons sprout, forms collaterals.Ectopic discharges along nerve axon, terminals & at DRG.SNS fibers invade DRG.Phenotypic switch in expression of neuropeptides like Sub P, CGRP.

Central Sensitization

Dorsal horn transmissionSignals onco-genes: c-fos & c-jun neuro-peptides and nerve growth factors alters patterns of nerve connections.

Opioids, LA, NMDA antagonist like ketamine & alfa-2 agonist clonidine suppress c-fos expression.

Central Sensitization

Central Reorganisation.Wind up (summation of signals)Up-regulation of NMDA receptorEctopic activityDepression inhibitory synapsesActivation of WDR cells.

Central re-organizationLong continued stimulation Central Reorganisation.

Ab fibres develops connections in lamina 2Allodynia. Area of pain increases along other nerve distribution. Loss descending inhibitory pathways

NMDA receptorAcute Pain AMPA receptors dislodges Mg from NMDA receptors activation of NMDA receptors.Activation of NMDA receptors.Increased signal transmissionRelease of NO, sub-P & PGs

Results of Central Sensitization Increased intensity of pain.Increased area of pain.Increased duration of pain.Decreased tolerability to pain.Development of psychological problems.Pain become non-responsive to conventional analgesics.

Symptoms of chronic painPain in the area of neuro-deficit. Allodynia, HyperalgesiaCharacter of pain: Burning, shooting, electric shock-like, stabbing pain.Associated symptoms: Numbness, tingling, pruritis, feeling of pin & needles.SMP: redness, edema, painful joint movements, decreased skin temperature, fall of hairs.

Problems of Chronic PainCentral Sensitization: altered anatomy and physiology of Pain processing pathway.Decreased pain threshold.Associated depression (due to decreased serotonin level).Existence of different Pain Cycles which are very difficult to break.

Treatment of Pain: MUTIMODAL APPROACH

Interventional Pain Management Combination analgesics Adjuvant therapy Physical medicinePsychological intervention

Treatment of Acute PainNSAIDs for very short periodParacetamol in adequate dosesTramadol + Paracetamol in adequate dosesRegional analgesia

Treatment of Chronic Pain with tissue damageStopping nociceptive inputsCorrecting neuropathy/ central sensitization

Treatment of Chronic Pain without tissue damageCorrecting neuropathy/ central sensitization

Treatment of Chronic Pain without tissue damageTreatment for peripheral sensitization Na-Channel blocker, Ca-Channel blockerTreatment for central sensitization NMDA antagonist, Ca-Channel blocker, opioids, drugs inhibiting Sub P, drugs enhances inhibitory synapses.Restoration of descending inhibitory pathways tramadol, tricyclics

Interventional Pain Management

Non-pharmacological methodsNon-opioidsWeak opioids +/- non-opioids +/- adjuvantStrong opioids

Recovery OperationTreatment of Pain

Non-opioidsWeak opioids +/- non-opioidsStrong opioidsRecovery OperationTreatment of Pain World of Misery Non-pharmacological methods

Non-opioidsWeak opioids +/- non-opioidsStrong opioidsRecovery OperationTreatment of PainNon-pharmacological methods

Interventional Pain Management are some minimally invasive procedures which gives permanent/long term pain relief by stopping nociceptive inputs or correcting neuropathy.It fills the gap between pharmacologic management of pain & more invasive operative procedure.

FAQs: What are the types of Pain?Acute Pain/ Nociceptive PainChronic Pain/ Neuropathic PainMixed type/ Combination of Nociceptive & Neuropathic Pain

FAQs:What is principle of treatment?Acute Pain: Treat disease/ Regional analgesia/ Paracetamol +opioid/ NSAIDsChronic Pain: Correct Neuropathy Tramadol+opioid/ TCA/ Anticonvulsant/ Clonidine/ IPM Mixed Pain: Stop Nociceptive input/ opioid+Paracetamol/ TCA/ Anticonvulsant/ Clonidine

FAQs:Why Ultracet is a very good analgesic for chronic pain?Can be used for years together even in renal failure and cardiac patients.Unlike NSAIDs, it has multidoal action which is very useful in chronic pain.Add TCA in burning pain/ Anticonvulsant in shooting pain/ Clonidine in cramping pain.It is the first line drug in all chronic pain.

Summary Multimodal approach is necessary for chronic pain.Interventional Pain Management works in most situations where all other options has failed.Combination analgesic therapy specially Tramadol + Paracetamol is very useful & ideal combination in treating moderate to severe chronic pain.Adjuvant therapy is necessary in most cases.Physiotherapy & Rehabilitation is essential too.