Pain teaching Muhammad Laklouk
Definition Pain An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. Sensory (discriminatiory) and affective (aversive) components.
Classification Acute vs Chronic Nociceptive vs Neuropathic Somatic vs Visceral (Referred pain)
Neuropathic pain: a pain arising as a direct consequence of a lesion or disease affecting the somatosensory system. Acute pain: Directly related to tissue injury, resolves when tissues heal. Chronic pain: pain that persists beyond normal healing time (> 3 to 6 months).
Allodynia Pain due to a stimulus that does not normally provoke pain. Dysesthesia An unpleasant abnormal sensation, whether spontaneous or evoked. Hyperalgesia Increased pain from a stimulus that normally provokes pain. Hyperpathia A painful syndrome characterized by an abnormally painful reaction to a stimulus, especially a repetitive stimulus, as well as an increased threshold.
Hypoalgesia Diminished pain in response to a normally painful stimulus. Paresthesia An abnormal sensation, whether spontaneous or evoked.
The nociceptive pathway Peripheral receptor 1 st order neuron 2 nd order neuron 3 rd order neuron
Pain transmission Peripheral sensitisation Primary hyperalgesia Tissue injury à Release of inflammatory mediatorsà drop in firing threshold of A delta & C fibers Changes in ion channels (phosphorylation of Sodium channel proteins) and TRPV1 receptors (increased expression).
Drugs that can reduce peripheral sensitisation:
Dorsal horn Release of glutamate from afferent terminals à Na influx à post synaptic depolarisation. Sustained afferent input à release of mediators (tachykinins)à removal of Magnesium plug on NMDA receptor à NMDA activation à post- synaptic potentials outlasting duration of triggering stimuli.
Inhibition of pain transmission
Central sensitisation Activation- dependent increase in excitability of nociceptive neurons at the dorsal horn. Mechanisms ü Wind- up ü Increased excitatory input ü Decreased inhibitory input ü Classical central sensitization
Windup: Repetitive firing of unmyelinated C fibres à Cumulative depolarization leads to the removal of voltage- dependent Mg 2+- channel block in NMDA receptors à summation of synaptic potentials (longer duration) Increased excitatory input: WDR neurons: large receptive fields, respond to noxious and non noxious stimuli, originate in deeper laminae Convergent Aβ input to WDR cells can now contribute to nociceptive activity à produces an area of centrally mediated hyperalgesia that spreads beyond the area of the initial injury (secondary hyperalgesia)
Decreased inhibitory input (descending pathways) Classical central sensitisation: changes in permeability of ion channels in DH, changes in expression of receptors in DH. Targets for pharmacological therapies?
TCA, SNRIs Gabapentinoids Tramadol Opiates Others (Ketamine, Cannabis)
Modulation and plasticity
Gate theory (examples?)
Examples of neuroplasticity Up- regulation / increased expression of receptors Wind up of the NMDA receptor in DH Re- organisation of the cerebral sensory cortex
Neuropathic pain conditions
CRPS CRPS type 1: not associated with nerve injury CRPS type 2: associated with nerve injury Budapest criteria:
CRPS usually occurs secondary to fractures, trivial soft tissue injury, tight cast or splint immobilization. In some cases, there might not be a history of any precipitating cause. F>M Upper extremity>lower Fracture most common precipitating event
Measurement in pain Uni- dimensional scales: NRS: 0 to 10 VAS (Gold standard in research) 100mm line: No pain at one end, worst imaginable pain on the other. VRS: no pain, mild, moderate, severe Sensitivity of each scale to small changes in pain Use in cognitive impairment, special populations
Multidimensional scales: McGill Pain Questionnaire (MPQ) and its Short Form. Consists of 20 subgroups of words describing sensory (10), affective (5), evaluative (1), and miscellaneous components of pain (4). Each subgroup has a list of words with a given ranking the word chosen by the patient with highest ranking is used for scoring. E.g, Thermal properties of pain, the word searing has a higher score than hot Pain rating index (PRI) is a sum of ranked scores. Present pain intensity (PPI) 0 to 5 scale
Brief pain inventory (BPI) The BPI is a 17- item self- rating scale. Patient indicates the site(s) of pain by shading a body diagram. 11- point NRS to assess the pain intensity in the preceding 24 h most, least, average, and right now, and degree of pain relief from current treatment. 11- point NRS of interference in seven domains of usual activities/functions and mood (e.g. work, sleep, mood, relations with other people)
Neuropathic pain scales: LANSS: Five sensory items and two clinical examination findings (allodynia and pinprick test). More than 12 points out of a maximum of 24 suggest that a neuropathic mechanism is likely to be contributory. DN 4: Six items related to symptoms and three physical examination findings PainDETECT: self- reported tool originally designed to distinguish neuropathic lower back pain from mechanical back pain. 1 Quality of life measurement Assessment of anxiety / depression
Stellate ganglion Fusion of the inferior cervical ganglion and 1 st thoracic ganglion Lies adjacent to the vertebral column between the carotid sheath and fascia overlying the prevertebral muscles. At the level of C7 / T1 (In front of TP of C7) Supplies sympathetic innervation to the head and neck and in part to the arm and cardiopulmonary plexuses.
Identification of Chassaignac s tubercule (transverse process of ) Fluoroscopic and USG technique Signs of a good block? - complications Indications: CRPS of the upper limb Post herpetic neuralgia Central stroke pain Phantom limb pain Ischaemic conditions of upper limb (Raynauds) Refractory angina Facial / cervical pain
Coeliac plexus 2 plexuses at the left and the right of the coeliac arterial trunk at its origin at the aorta at the level of L1. Receives preganglionic fibers from the greater splanchnic nerve (T5-10), lesser splanchnic nerve (T9-11) and least splanchnic nerve (T12). Can relieve pain originating from Pancreas, stomach, liver, gall bladder, spleen, kidneys, small bowel and proximal two- thirds of the large bowel.
Local anaesthetic vs Neurolytic block Complications?
Low back pain Causes Structural / mechanical Neurogenic Inflammatory Neoplasm Infection Metabolic Referred pain
Red flags in LBP History and examination Interventions (facet blocks, RF lesioning, epidural steroids)