Neuropathic pain in spinal cord injury: significance of clinical and electrophysiological measures

A large percentage of spinal cord-injured subjects suffer from neuropathic pain below the level of the lesion (bNP). The neural mechanisms underlying this condition are not clear. The aim of this study was to elucidate the general effects of spinal deafferentiation and of bNP on electroencephalographic (EEG) activity. In addition, the relationship between the presence of bNP and impaired function of the spinothalamic tract was studied. Measurements were performed in complete and incomplete spinal cord-injured subjects with and without bNP as well as in a healthy control group. Spinothalamic tract function, assessed by contact heat evoked potentials, did not differ between subjects with and without bNP; nevertheless, it was impaired in 94% of subjects suffering from bNP. In the EEG recordings, the degree of deafferentiation was reflected in a slowing of EEG peak frequency in the 6–12-Hz band. Taking into account this unspecific effect, spinal cord-injured subjects with bNP showed significantly slower EEG activity than subjects without bNP. A discrimination analysis in the subjects with spinothalamic tract dysfunction correctly classified 84% of subjects as belonging to either the group with bNP or the group without bNP, according to their EEG peak frequency. These findings could be helpful for both the development of an objective diagnosis of bNP and for testing the effectiveness of new therapeutic agents.