Reafferentation and prosthetic function alleviates phantom pain in patients with brachial plexus avulsion injuries
Most patients who suffer brachial plexus injury, leading to spinal cord root avulsion, suffer from a continuous crushing and burning as well as intermittent electrical shooting-like pain, typically of severe and devastating nature.
Due to complete deafferentation of a limb the generation of a phantom limb as it occurs after limb amputation is frequently observed. Sensory stimulation leading to abnormal perception including phantom sensations have been associated with reorganization of the somatosensory cortex.
In cases where immediate surgical repair (reimplantation of avulsed roots to the spinal cord) is not possible, selective nerve transfers offer a new technique to restore limb function and also to significantly reduce deafferentation pain. The nerves that are redirected to denervated muscles in the affected limb reinnervate those target muscles and the overlying skin. Although proper muscle movements cannot be achieved, the newly emerging myoelectric signals (produced by intuitive cognitive control of the patient) can be used to control a prosthesis 6-12 months post surgery. The final outcome after a time frame of 1,5 to 2 years is a functional arm that is intuitively controlled by the patient. The elective amputation of the withered, painful arm is therefore required.
Since exercise has been successfully shown to promote axonal regeneration and modulate plasticity in the spinal cord after nerve injury, it is reasonable to propose that the transferred nerves restore proper neuromuscular junctions. They may also provide useful sensory feedback via muscle spindles and other proprioceptive input. Unilateral chronic pain from various origins has been associated with cortical reorganization in primary somatosensory areas. The reduction in pain intensity has been found to correlate with the recovery of somatotopic remapping in all mentioned conditions. We therefore assume that the combination of motoric re-education and regained sensory input to the central nervous system via selective nerve transfers and prosthetic treatment accounts for the reduction or disappearance of pain in the affected limb and also for the reversion of pain-associated central mechanisms.
Phantom Pain after TMR
Neuroma pain and Phantom Limb Pain (PLP) is very common in upper limb amputees. Targeted muscle reinnervation (TMR) provides a good opportunity to prevent neuroma formation, because the nerves responsible for the neuroma are rerouted to muscles in the stump. Additionally, some patients reported an increase in pain directly after surgery and they felt less PLP with ongoing rehabilitation and prosthetic fitting. Since PLP is a burden for these patients, and there is no known satisfying therapy yet, this effect of TMR is to be studied in greater detail.
Tactile discrimination training alleviates phantom limb pain
Phantom limb pain can result as a consequence of deafferentiation after amputation, affecting a high percentage of amputees. Behaviorally relevant stimulation can alleviate both cortical reorganization and phantom limb pain (Flor et al 2006). One example is using a myoelectric prosthesis. Another possibility is discrimination training, which offers input to the amputation zone and thereby may change reorganization (Flor et al 2001, Moseley 2009). Flor and collegues (2001) used electrical stimulation over a period of 2 weeks and achieved a significant reduction in pain and cortical reorganization, compared to standard medical and psychological treatment.