Somatosensory Evoked Potentials as an Aid in the Diagnosis and Intraoperative Management of Spinal Stenosis

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Abstract
The use of somatosensory evoked potentials (SEP) in localizing the level, extent and laterality of nerve root entrapment is clinically important. In patients with lumbar spinal stenosis, this is especially true. Patients (20) with preoperative SEP were studied of which 11 patients had intraoperative SEP correlated with their computed tomographic (CT) scan and/or myelographic findings. A high incidence of 4th and 5th lumbar and 1st sacral nerve root involvement was confirmed. The posterior tibial nerve was abnormal in 95%, the peroneal in 90% and the sural in 60% in the symptomatical lower extremity. Upper lumbar segments were barely affected as evident by the low incidence of saphenous nerve abnormality in only 12% of the patients. The posterior tibial nerve had the highest yield and was useful for screening. Bilateral lower extremity abnormalities were found in 7 of 20 cases studied with 2 patients having bilateral symptoms and findings. Bilateral lower extremity SEP evaluation can reveal previously unsuspected pathology and is strongly recommended in preoperative evaluations. SEP can serve as a useful intraoperative tool to guide the surgeon during a decompressive surgical procedure. SEP are specifically helpful in spinal stenosis with a paucity of clinical findings and equivocal CT scan or myelographic studies. SEP seem much more sensitive and effective than conventional electrodiagnostic tests in detecting spinal nerve root compression secondary to spinal stenosis.

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