Peripheral and central effects of nerve regeneration : Experimental and clinical studies

Sammanfattning: A nerve injury in the hand often results in profound abnmmalities in sensory perception despite careful alignment and microsurgical repair in order to facilitate accurate nerve regeneration. The present experimental and clinical studies were undertaken in an attempt to functionally evaluate peripheral and central effects of nerve regeneration.In the experimental studies the rat foot was used as a model for the human hand. Three months after neurotomy and repair a flUlctional evaluation was performed of regenerated and misrouted polymodal nociceptor C-fibers and low-threshold mechanoreceptive axons by mechanical stimulation on the foot and electrical recordings proximal to the lesion and by Evans blue albumin extravasation.It was found that 1) functional regeneration of misrouted axons related to polymodal nociceptive units and low-threshold mechanoreceptive units is more efficient in hairy skin of the rat foot whereas only misrouted polymodal nociceptor C-fibers recover function in glabrous skin, 2) following epineural suture and repair with a silicone tube after sciatic neurotomy there is similar effect on the regeneration of polymodal C-fibers after three months, and 3) functional regeneration of C-fibers is more successful in 3-month-old than in new-born rats.In the clinical studies the functional effects of median nerve injury and regeneration were evaluated by two-point discrimination test, electroneurography, somatosensory evoked potentials and functional magnetic resonance imaging (IMRI). A method oftMRI during tactile stimulation was developed, and the normal cortical activation during stimulation was studied in 12 healthy volunteers.The effects of nerve injury were studied in 6 injured adult men 15-55 months after median nerve injury and repair. It was found that 1) the 2-point discrimination was > 15 mm, 2) the nerve conduction velocity and signal amplitude were decreased in the severed nerve segment, but the cortical evoked response was normal at nerve stimulation proximal to the lesion, 3) tactile stimulation of the glabrous skin of the hand in healthy volunteers caused bilateral cortical activation (fMRI) in the primary somatosensory cortex, 4) a loss of sensory discrimination in the hand after median nerve injury was associated with a normal or even elevated activation (fMRI) in the somatosensory cortex during tactile stimulation of the digit IT-m.