pain - defintions and mechanisms Flashcards
what is pain?
an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
describe the cartesian model
-it describe pain as a mechanical process in which pain signals travel from the body to the brain
-the model treats pain as a physical process
-however, there is much more to pain than this - ie emotions etc can cause pain
what are the different types of nociceptors?
-A Delta fibres- mechanical, fast pain
-C fibres - polymodal, slow pain
what is hyperalgesia?
increased pain from a stimulus that normally provokes pain
what’s the difference between primary and secondary hyperalgesia?
- primary: increased sensitivity to input at the site of the injury and due to process in damaged tissues: it is largely due to the sensitisation of peripheral nociceptors
- secondary hyperalgesia: sensitivity in uninjured tissue around the original injury. likely to arise from central mechanisms
define allodynia
pain evoked by stimuli that are not normally painful
eg touch or cold / heat
define neuropathic pain
-pain caused by a lesion or disease of the somatosensory nervous system
define nociplastic pain
pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing pain
eg fibromyalgia, migrane
what is central sensitisation?
increased responsiveness of nociceptive neuron’s in the CNS to their normal or sub threshold afferent input
what is peripheral sensitisation?
-increased responsiveness and reduced threshold of nociceptive neurons in the periphery to the stimulation of their receptive fields
define neuropathy
a disturbance of function or pathological change in a nerve eg radiculopathy
what is peripheral neuropathic pain?
pain caused by a lesion or disease of the peripheral somatosensory nervous system eg shoulder subluxation + nerve damage
what is central neuropathic pain?
-pain caused by lesion or disease of the central somatosensory nervous system eg stroke - pain after stroke
what are the 3 main pain types?
-nociceptive
-neuropathic
-nociplastic
what is nociceptive pain (somatic pain)?
-dull, deep, aching somatic type pain (ie coming from tissues)
-mechanical/ physiological processes in injured tissue: tends to be relatively localised (but referred pain is possible)
-predictable response to stretch, compression or movement
-responds to simple painkillers and NSAIDs
what is inflammatory nociceptive pain?
-inflammatory pain can be associated with acute tissue damage, infection or active inflammatory conditions such as RA
describe the clinical criteria of nociceptive pain
-pain localised to the area of injury/ dysfunction
-clear proportionate mechanical/ anatomical nature to agg and easing factors
-usually intermittent and sharp with movement or mechanical provocation, may be more constant dull ache or throb at rest
what does nociceptive pain not normally include according to the clinical criteria?
-night pain and disturbed sleep
-antalgic postures / movement patterns
- pain described as burning, shooting, sharp or electric shock like
-pain associated with other dysaesthesias eg pain from touch
what are the main points with neuropathic pain in MSK?
-patient will report superficial, burning, shooting, cramping with all or part of nerve innervation field (dermatome or cutaneous field)
-+/- pins and needles and possible muscle weakness and autonomic changes
-sometimes allodynia (pain due to stimulus that usually docent cause pain)
-often difficult to ease with rest or painkillers eg NSAIDs
-provoked by neurodynamic tests, compression or nerve palpation
-response to passive treatment varies
describe the clinical criteria for neuropathic pain
-pain referred in a dermatomal or cutaneous distribution eg L5 dermatome in L5 radiculopathy
-history of nerve injury, pathology or mechanical compromise
-pain or symptom provocation with mechanical/ movement tests eg active / passive, neurodynamic that move, load or compress tissue
describe primary vs secondary chronic pain
chronic primary pain - nociplastic ie pain arising from altered nociceptors despite no clear evidence of actual tissue damage
describe chronic secondary pain
-could be persistent nociceptive (somatic) or neuropathic or mix of both
describe the pain mechanism of nociplastic pain
-called central sensitisation
-wide spread pain with non anatomical distribution
-ongoing pain after healing with hyperalgesia + allodynia
-inconsistent response to stimuli and tests ie physical exam
-pain seems to have a mind of its own (when taking pain history, aggs + eases)
-can be easily aggravated by emotion etc
-abnormal neural activity due to disease or injury
describe the cluster (smart 2012) 3 symptoms and 1 sign predictive of central sensitisation pain
-disproportionate, non mechanical and unpredictable pattern of pain in response to multiple non specific factors
-pai disproportionate to the nature and extent of injury or pathology
-strong association with maladaptive psychosocial factors eg emotions, maladaptive beliefs, poor self efficacy etc
-diffuse non anatomic areas of pain or tenderness on palpation (ie everything hurts)
what is mixed pain?
a combination of various pain types for eg nociceptive and neuropathic pain components in an individuals with LBP and painful lumbar radiculopathy
- or neuropathic pain combined with functional pain (sciatic and irritable bowel or fibromyalgia)
what are the management strategies for neuropathic pain?
-manual Rx may readily provoke symptoms until pain controlled
-specific pharmacological rx eg antidepressants, opioids, topical rx etc
what pain type is discogenic LBP?
nociceptive
what type of pain if radiculopathy?
-neuropathic or nociceptive or mixed
what type of pain is mechanical LBP associated with?
nociceptive
