Alteration of the somatosensory cortical map in peripheral mononeuropathy due to carpal tunnel syndrome

Substantial plasticity of the mature mammalian somatosensory cortex was demonstrated after deprivation of sensory input produced by amputation or somatosensory deafferentation. Following transection of the median nerve, adult owl and squirrel monkeys exhibit extensive reorganization in the cortical representation of the hand in areas 3b and 1. In the present study we investigated the possible effect of incomplete median nerve damage on sensory cortex somatotopy in a patient with unilateral carpal tunnel syndrome. We assessed interhemispheric differences of the hand representation in SI by means of magnetic source imaging. Additional intersubject data comparison was performed for specific results on the basis of available normal data from the literature and from own investigations in five healthy volunteers. Our results demonstrated a decreased extension of the cortical zone representing the injured median nerve and suggested invasion of the deprived area by cortical sectors receiving inputs from the little finger (supplied by the ulnar nerve) and from the dorsum of the thumb (innervated by the radial nerve). The study indicates topographic rearrangement of the hand representational zone in the human primary somatosensory cortex in a case of chronic median nerve injury.