Pathophysiology Phantom pain

1 pathophysiology

1.1 peripheral mechanisms
1.2 spinal mechanisms
1.3 central mechanisms , cortical remapping

1.3.1 neuromatrix

pathophysiology

the neurological basis , mechanisms phantom limb pain derived experimental theories , observations. little known true mechanism causing phantom pains, , many theories highly overlap. historically, phantom pains thought originate neuromas located @ stump tip. traumatic neuromas, or non-tumor nerve injuries, arise surgeries , result abnormal growth of injured nerve fibers. although stump neuromas contribute phantom pains, not sole cause. because patients congenital limb deficiency can sometimes, although rarely, experience phantom pains. suggests there central representation of limb responsible painful sensations. currently, theories based on altered neurological pathways , cortical reorganization.

peripheral mechanisms

neuromas formed injured nerve endings @ stump site able fire abnormal action potentials, , historically thought main cause of phantom limb pain. although neuromas able contribute phantom pain, pain not eliminated when peripheral nerves treated conduction blocking agents. physical stimulation of neuromas can increase c fiber activity, increasing phantom pain, pain still persists once neuromas have ceased firing action potentials. peripheral nervous system thought have @ modulation effect on phantom limb pain.

spinal mechanisms

in addition peripheral mechanisms, spinal mechanisms thought have influencing role in phantom pains. peripheral nerve injury can lead degeneration of c fibers in dorsal horn of spinal cord, , terminating fibers may subsequently branch same lamina. if occurs, fiber inputs reported noxious stimuli. substance p, involved in transmission of pain signals, expressed aδ , c fibers, following peripheral nerve damage, substance p expressed aβ fibers. leads hyperexcitability of spinal cord, occurs in presence of noxious stimuli. because patients complete spinal cord injury have experienced phantom pains, there must underlying central mechanism responsible generation of phantom pains.

central mechanisms , cortical remapping

under ordinary circumstances, genetically determined circuitry in brain remains largely stable throughout life. thought, until 30 years ago, no new neural circuits formed in adult mammalian brain. recently, functional mri studies in amputees have shown patients have experienced motor cortical remapping. majority of motor reorganization has occurred downward shift of hand area of cortex onto area of face representation, lips. there side shift of hand motor cortex ipsilateral cortex. in patients phantom limb pain, reorganization great enough cause change in cortical lip representation hand areas during lip movements. has been found there high correlation between magnitude of phantom limb pain , extent shift of cortical representation of mouth hand area in motor , somatosensory cortical reorganization has occurred. additionally, phantom pains in upper extremity amputees increased, there higher degree of medial shift of facial motor representation. there multiple theories try explain how cortical remapping occurs in amputees, none have been supported great extent.

the neuromatrix

the neuromatrix theory proposes there extensive network connecting thalamus , cortex, , cortex , limbic system. theory extends beyond body schema theory , incorporates conscious awareness of oneself. theory proposes conscious awareness , perception of self generated in brain via patterns of input can modified different perceptual inputs. network genetically predetermined, , modified throughout one’s lifetime various sensory inputs create neurosignature. neurosignature of specific body part determines how consciously perceived. input systems contributing neurosignature somatosensory, limbic, , thalamocortical systems. neuromatrix theory aims explain how activities associated pain lead conscious perception of phantom pain. persistence of neurosignature, after limb amputation, may cause of phantom sensations , pain. phantom pain may arise abnormal reorganization in neuromatrix pre-existing pain state.

opposition neuromatrix theory exists largely because fails explain why relief phantom sensations eliminates phantom pains. not address how sensations can spontaneously end , how amputees not experience phantom sensations @ all. in addition, major limitation of neuromatrix theory broadly accounts various aspects of phantom limb perception. difficult tested empirically, when testing painless phantom sensations.