Pain general charateristics

Definition: unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

Threshold: if the intensity of the stimulus is below threshold (subthreshold) pain is not perceived. As the intensity increase more and more pain is felt more and more.

Adaptation: no adaptation of pain receptors

Rate of damage: if the rate of injury is high the pain is high

General clinical features

It has been considered the fifth vital sign

Mnemonics:

WHAT'S UP:

w: where
is the pain 
location: look below, site of pain, following classifications and somatic mapping (site of the pain, useful for organ type diagnosis, like neuropathic or nociceptive, and organ diagnosis, namely what nerve or organ is involved) 

h: how's the pain feel (quality)
Dual nature of pain (classification's feature, useful for source superficial/deep diagnosis)
- fast pain:  also known as acute, pricking, sharp. Easily localized. short duration. Not felt in the deep visceral organs (superficial pain). A delta receptors.
- slow pain: also known as throbbing, aching, chronic. Poorly localized. Long duration. It can occur everywhere (usually somatic deep pain and visceral/referred pain). C receptors
a: aggravating and alleviating factors

t: timing. When did the pain start? intermittent, continous?
Duration (classification's feature, useful for diagnosis of pathology type and noxious stimuli):
- acute: usually of recent onset and commonly associated with specific injury, lasting from seconds to six months
- chronic: constant or intermittent pain that persists beyond the expected healing time and seldom attributed to a specific cause or injury; lasts for 6 months or longer. Ex: inflammatory chronic diseases, neuropathic pain
- - chronic non malignant (benign) pain: non life threatening that nevertheless persists beyond the expected time for healing (ex: phantom limb pain). 
- - recurrent acute pain: relatively well defined episodes of pain interspersed with pain-free episodes. Example: migrain, neuralgia (recurrent episodes of intense shooting or stabbing pain), causalgia (recurrent episodes of severe burning pain)

s: severity. How bad the pain is
Measurement
scales: visual analog scale (VAS, a line), numeric scale (0-10), color scale, faces pain rating scale, simple descritptive pain intensity scale (based on words)
written pain scale can't be used if patient is seriously ill, in a sever pain, or if he just returned from surgery
Useful to assess the effectiveness of interventions




U: useful data. What other symptoms are you experiencing (useful for diagnosis on real duration and source of pain)
Associations: sweating, increased heart rate, increased pressure, behavioural changes (bracing, guarding or holding the painful area, moaning, grimacing, crying, talking about pain)
- acute pain: possible associations are tachicardya, rapid and shallow respirations, increased BP, dilated pupils, sweating and pallor. Physiologic association may be extinguished in patient with chronic pain
- chronic pain: possible associations are depression, withdraw from social activity, immobility, irritability, controlling attitude. 



p: perception. What's the patient perception on what caused the pain 
relation with stimuli (differentiation between pain and pain related terms, see classification according to stimuli)
example: activity before the pain and pain related positions (useful for source diagnosis)


Central processing of nociception

 

Components of somatosensory system


 


Alfa and Omega


Pain sensation is somewhat poorly localized . However superficial pain is comparatively better localized than deep pain

Alfa

 

- the presence of noxious stimuli:
- - if the stimuli is noxious (external or internal, like inflammation)
- - If the stimuli is not noxius we can call the symptom Allodynia
- - If there is no real  possible stimuli: phantom limb pain

- The source of pain is that area of the body from which the pain actually originates.
- - visceral: pain occurring in a visceral structure is not usually felt in the viscus itself (viscus is insensitive to most of the sensory stimuli) but on the surface of the body or in some other somatic structure that may be located quite some distance away (referred pain). Quality: deep, squeezing, dull
Visceral pain come from the following origins: typical of visceral organs, visceral peritoneum and mesenteries.
It can arise from
- - - Ischemia: coronary artery occlusion resulting in myocardial ischemia, Cardiac pain
- - - Obstruction of a hollow viscus: here the part proximal to obstruction contract violently so intestinal colic results. Pain is due to the contraction of the smooth muscles causing traction of the mesentery leading to pain (intestinal obstruction, gallstones, uretere stones)
- - - Inflammation: pain is due to associated spasm of smooth muscles
- - - Distension: too much distension of a hollow viscus can produce pain
- - . chemical damage to a viscus or covering peritoneum (gastric ulcer)
- - somatic
- - - superficial (skin): sharp. Easily localized
- - - deep (muscles, tendons, bones, fascias, parietal peritoneum): dull, aching. Can be referred 



Pain receptors are:
Adelta: fast, high conductive speed, sensitive to machanical noxious stimuli, small, myelinated
C: slow, slow conductive speed, sensitive to many stimuli, small, unmyelinated

Omega


The site of pain is the location that the patient feels the pain. The site of pain is located by asking the patient to point out the region of the body that is painful (remember to ask the patient to touch the area of pain if possible since some patients are not able to locate properly pain with words since they do not have a proper knowledge of anatomy terms). 

Brigde 


White matter: ascending and descending fibers organized in distinct bundles which occupy particular areas and regions in the white matter.  

The tract is a bundle of nerve fibers having the same origin, course, destination and function. In general long tracts are located peripherally, while shorter tracts are located near the gray matter. The axons within each tracts are grouped according to the body region innervated.
intersegmental (propriospinal): fibers interconnecting adjacent or distant segments of the spinal cord 
Gray matter
: organized in 
- nuclei
- horns: dorsal (sensory), ventral (mostly motor) and lateral (autonomic)


Sensory pattern

First order sensory neuron: cell body located in the dorsal root ganglion. Carry signals from the periphery to the spinal cord through the dorsal root of spinal cord
Second order sensory neuron: cell body in dorsal gray column or various sensory nuclei of the brainstem.  Relay this information from the spinal cord to the thalamus. Thalamus allow a person to be aware of the pain. Lesion of thalamus produce several types of pain known as "Thalamic pain"
Third order sensory neuron:  cell body in thalamic nuclei. transmit the information from the thalamus to the primary sensory cortex, where the information is processed. Cortex allows the judgement on pain intensity, pain location, and produces emotional and motor answers to pain




Information is sent to the primary sensory cortex on the opposite side of the body

Most of the sensory information is processed in the spinal cord, thalamus or brainstem.  Only 1% reach the cerebral cortex and our conscious awareness. 

Pain pattern

ascending pain pathway: Spinothalamic track. Fibers are highly somatothopic arranged with those of the lower limb lying most superficially and those of the upper limb lying deeply
- anterior ventral: immediate warning of presence, location, intensity of an injury. Lateral and ventral to the ventral horn
- - pain an thermal sensation in lateral tract
- - non discriminative touch and pressure in medial tract
- lateral: slow aching reminder that tissue damage has occured

descending pain pathway: pain inhibition

Information is sent to the primary sensory cortex on the opposite side of the body

Classifications of pain and pain related terms

according to the quality 
- pricking, sharp, easily localized: fast (somatic superficial) 
- throbbing, aching, poorly localized: slow (somatic deep  and visceral/referred or dysfunctional)
- bright and burning: peripheric neuropathy 
- strange sensation: paraeshesia


according to the source of pain
- somatic pain (somathestetic)
- - superficial (from skin and subcutaneous tissues: superficial cuts/burns, easily localized, sharp)
- - deep (from muscle/bones/fascial/periostium; like fractures, arthritis, fibrositis, rupture of muscles etc; dull, aching, sometimes referred)
- visceral pain: from visceral structure, dull and deep, often referred

according to the relation between site of pain and source of pain:
- primary pain (same site) 
- heterotopic pain (different site)
- - neuropathic (somatosensory nervous system)
- - - central (source: CNS; ex: stroke or parkinson) 
- - - projected (source: nerve or root, peripheric)
- - - - sensory (source: sensory root or main nerve); burning and bright (ex: herpes zoster or diabetic neuropathy)
- - - - motor (source: motor root major motor nerve)
- - nociceptive (arises from actual or threatened damage to non neural tissue and is due to the activation of nociceptors)
- - - referred (nociceptive source), poorly localized, dull

According to the site of pain
. neuralgia: pain in the distribution of nerve or nerves

According to the part of somatosensory system or mechanism involved (useful for therapy)
- psichogenic (pain as an emotional experience)
- neuropathic (somatosensory nervous system)
- - central
- - peripheric
- nociceptive (arises from actual or threatened damage to non neural tissue and is due to the activation of nociceptors)
- inflammatory
- dysfunctional

According to the stimuli and answer to stimuli
- no real stimuli: phantom limb
- other stimuli perceived as pain: allodynia
- dysfunctional amplification of normal sensory signal: dysfunctional pain (fibromyalgia, irritable bowel syndrome, tension headache, temporomandibular joint disease, interstitial cystitis)
- augmented answer to noxious stimuli: hyperalgesia
- diminished answer to noxious stimuli: hypoalgesia
- no answer to noxious stimuli: analgesia
- no answer to any stimuli: anaesthesia