Motor and somatosensory evoked potentials in cervical spondylotic myelopathy

We recorded upper and lower limb MEPs and SEPs in 55 patients with clinically suggestive and myelography-documented cervical cord compression due to spondylotic changes. MEPs were abnormal in biceps brachii of 21 patients (38%), in first dorsal interosseous muscle of the hand of 49 patients (89%) and in tibialis anterior of 47 patients (85%). Overall, MEP abnormalities were present in at least one muscle of 51/55 patients (93%). Median SEPs were abnormal in 20 cases (36%), ulnar SEPs in 24 (44%) and posterior tibial SEPs in 40 (73%). Overall incidence of SEP alterations was 73% (40/55) and SEPs detected clinically silent sensory dysfunction in 10 patients (18%). Among the 43 patients who underwent surgical decompression, first dorsal interosseous (FDI) MEPs and tibial SEPs remained abnormal in most cases 1 year after surgery, independently of clinical outcome. On the other hand, serial EP studies seemed useful to confirm and monitor the clinical evolution of unoperated patients.