amputation: the role of central factors

Dynamic changes in somatosensory cortical maps are known to occur in experimental animals subjected to peripheral nerve transection or amputation. To study the sensory effects of central nervous system adaptation to temporary or permanent loss of input from a part of the hand, multimodality quantitative sensory tests were carried out in 11 patients with complete traumatic division and repair of the median or ulnar nerves and in six patients who had undergone amputation of one or more digits. As expected, vibration, two point discrimination, and tactile thresholds were raised in the territory of the injured nerve in a graded fashion, sensitivity being poorest in the patients with the most recent injuries. Surprisingly, localisation was better in the tips than at the base of the hypoaesthetic fingers, suggesting a central attentional gradient. Stimulus-response curves conformed to a power function whose exponent was higher in denervated than in normal skin. Changes in psychophysical functions were also discernible in the intact hand. There was no hyperaesthesia in the territory of the nerve adjacent to the injured one or in the stump in the case of amputees. Central factors contribute to the sensory changes seen after nerve injury, but the functional effects of the cortical reorganisation that follows partial deafferentation are more subtle than a simple heightening of sensitivity in the surrounding skin. (7 Neurol Neurosurg Psychiatry 1993;56:393-399) Department of Neurology, Manchester Royal Infirmary, Manchester M13 9WL S Braune W Schady Correspondence to Dr W Schady, Department of Neurology, Manchester Royal Infirmary, Oxford Road, Manchester, M13 9WL, UK Received 6 January 1992 and in revised form 3 July 1992. Accepted 29 July 1992 The body surface is represented somatotopically in the mammalian somatosensory cortex. It has been shown, however, that cortical maps in rodents and monkeys can change during adult life in response to deafferentation. Within weeks or months of upper limb nerve transection the region of cortex serving the area of denervated skin, which initially falls silent, is taken over by inputs from other parts of the hand (for a review see Wall'). There is a wealth of information on the sensory events that follow nerve injury and regeneration in humans. Much less is known about the relative contribution of peripheral and central factors to functional recovery of sensation. It is self evident that unless the skin is reinnervated it will remain anaesthetic. As nerve fibres grow back to the skin from the site of injury, possibly with some contribution from collateral sprouting,2 the patient's sensory experience will be determined by the number and type of axons that establish functional connections with cutaneous receptors, by changes in the encoding properties of regenerated fibres, and by the brain's response to the initial sensory deprivation and subsequent return of afferent activity. If a similar reorganisation in cortical maps occurs in humans as in animals after partial deafferentation, information from newly reinnervated cutaneous receptors might not be processed normally because their original cortical representation had been "taken over" by inputs arising elsewhere. In addition, cutaneous sensibility in the area surrounding the anaesthetic skin might be altered by its increased representation in the somatosensory cortex. The principal aim of our study was to assess the functional sensory effects of central nervous system adaptation to temporary (nerve injury) or permanent (amputation) loss of input from a part of the hand. Materials and methods