Evidence for cortical reorganization in patients with deafferentation pain after brachial plexus injury

Abstract

Brachial plexus injury (BPI) is a severe upper limb injury. Patients not only suffer from arm and hand function loss but experience neuropathic pain in the affected limb. This presence of pain despite a sensory loss is reminiscent of phantom limb pain (PLP) in arm amputees. Previous studies found a connection between PLP after sensory deprivation and an enlargement or shift of the areas representing the lips into the hand area in the primary somatosensory cortex (S1). This study investigates maladaptive changes in patients with pain caused by deafferentation after BPI, compares the cortical reorganization and pain characteristics with amputees, and investigates the link between cortical changes and pain intensity. The study included 3 BPI patients and 3 amputees. Somatosensory evoked fields after tactile stimulation of both corners of the lips and the phalanx of the thumb are measured using magnetoencephalography to estimate their representations in S1. The affected thumb's representation is estimated by mirroring the healthy thumb's localization along the longitudinal fissure. All patients show a reduced distance between lip and affected thumb representation and a distance between lip representations exceeding that in healthy individuals. Results indicate no difference in pain characteristics and reorganization between patients' groups. Pain and the amount of reorganization do not correlate. The study suggests cortical reorganization in patients with BPI and neuropathic pain in the affected limb, similar to amputees with PLP. Therapeutic approaches for PLP could be transferred to improve pain treatment in BPI patients.