Diagnostic utility of somatosensory evoked potentials (SEPs) in presurgical assessment of cervical spondylotic myelopathy.

Median and tibial nerve SEPs were recorded in 27 patients with spondylotic myelopathy. SEP data were compared with clinical and MRI data. SEPs were abnormal in all but five patients. Segmental dysfuction of the cervical cord was observed in 12 patients (45%), whereas abnormality of dorsal column conduction was observed in 10 (37%) and 16 (59.3%) patients after median and tibial nerve stimulation, respectively. No clear correlation was found between the severity of MRI abnormalities and that of clinical presentation or SEP abnormalities. However, there was no patient with normal SEPs and severe MRI abnormalities, including narrowing of cervical cord diameter or impingement of the cervical cord or intramedullary T2 signal hyper intensity. Conversely, 8 of the 13 patients with no evidence of cord narrowing or T2 signal abnormality showed abnormal SEPs. This divergence between SEP and MRI data suggests that SEP recording should be included in presurgical assessment of these patients, especially those without clear MRI evidence of cervical cord compression.