Peripheral nervous system origin of phantom limb pain

Area of Science:

• Neuroscience
• Pain Research
• Surgical Anatomy

Background:

• Most amputees experience phantom limb sensations, with many suffering from chronic phantom limb pain (PLP).
• The prevailing theory attributes PLP to maladaptive cortical plasticity following sensory loss.
• An alternative hypothesis suggests PLP originates from exaggerated neuronal activity in dorsal root ganglia (DRGs).

Purpose of the Study:

• To investigate the hypothesis that phantom limb pain (PLP) is a bottom-up process driven by ectopic activity in axotomized primary afferent neurons within the dorsal root ganglia (DRGs).
• To assess the efficacy of localized anesthetic blockade of DRGs in alleviating PLP and non-painful phantom limb sensations (npPLS).

Main Methods:

• Conducted a study involving 31 amputees experiencing PLP and/or npPLS.
• Administered local anesthetic lidocaine intrathecally and/or directly to the DRG surface via intraforaminal epidural block.
• Utilized control injections and varying lidocaine concentrations to differentiate effects.

Main Results:

• Intrathecal and/or intraforaminal lidocaine application rapidly and reversibly abolished both PLP and npPLS in participants.
• Control injections did not produce these effects.
• The therapeutic effect of intraforaminal block was topographically specific to the denervated limb.
• Low lidocaine concentrations, sufficient to inhibit DRG ectopia but not nerve impulse propagation, also suppressed PLP and npPLS.

Conclusions:

• Phantom limb pain (PLP) is primarily driven by abnormal activity generated within the dorsal root ganglia (DRGs).
• The DRG is a viable and recommended target for therapeutic interventions aimed at treating PLP.
• These findings suggest potential for treating other regional neuropathic pain conditions by targeting DRG activity.