Predicting Nerve Root Pathology With Voltage-actuated Sensory Nerve Conduction Threshold

摘要

Voltage-actuated sensory nerve conduction threshold (V-sNCT) is a quantitative test of sensory function. This study compares the sensitivity, specificity, and predictive value of V-sNCT compared to physical examination for the presence of nerve-root adhesions visible on epidurogram. Predicted abnormal nerve roots by V-sNCT and/or physical examination were compared with abnormal nerve roots documented by abnormal epidurogram in forty-nine patients with L5/S1 radicular back pain. Sensitivity, specificity, and predictive value for V-sNCT predicting nerve root pathology were 94.6%, 70.2%, and 91.0%, respectively, compared to 61.7%, 72.3%, and 87.6%, respectively, for prediction by physical examination alone. In addition, area under ROC Curve and relative risk for V-sNCT were significantly more predictive of nerve-root pathology than physical examination (p<0.05). Prediction of abnormal nerve-root pathology with V-sNCT is superior to prediction from neurological examination. Introduction Sensory neurological examination is an important part of any physical examination. This part of the physical examination takes on even more importance in the workup of the patient with chronic pain. During World War II, Dr. George Riddoch, a neurologist in the British Army, developed a logical approach to the sensory examination with the concept of identifying “signature” surface areas highly correlated with specific anatomic dermatomes, which, in turn, are associated with specific nerve roots.1 Later, the concept of current perception threshold (CPT) was developed to quantitate level of sensory deficit.2 Problems developed with this diagnostic technique, however, with significant variability associated with changing skin resistance.3 Recently, the concept of voltage-actuated sensory nerve conduction (V-sNCT) has resulted in the development of a new instrument to quantitate sensory function (Medi-Dx 7000, Neuro-Diagnotic Associates, Inc., Laguna Beach, CA). This instrument provides testing which is voltage mediated, and results are independent of changes in skin resistance. The purpose of this study was to assess how well V-sNCT worked in predicting nerve root pathology as defined by filling defects on epidurogram prior to epidural lysis of adhesions. Methods After IRB approval and informed consent, patients with L5 or S1 radicular back pain scheduled for lysis of epidural adhesions4 were studied. All patients underwent pre-procedure V-sNCT testing. All patients received catheter-directed lysis of adhesions, during which an epidurogram was done with 10 ml of Omnipaque-180 contrast. Predicted abnormal nerve roots identified by V-sNCT prior to the procedure were compared with abnormal nerve roots documented by abnormal epidurography of the nerve root. In addition, neurological examinations were conducted relating to the nerve roots tested. Neurological examination for L5 and S1 nerve roots were conducted as described by Hoppenfeld.5 Neurological exam associated with L5 and S1 consisted of a motor, reflex (except for L5), and sensory test. Motor test for L5 was to test dorsiflexion of the big toe with the extensor hallucis longus. The examiner supported the patient's foot with one hand around the calcaneus and then placed his/her thumb in such a position that the patient must dorsifex his/her great toe to reach it. The examiner opposed the dorsiflexion by placing his/her thumb on the nail bed of the great toe and fingers on the ball of the foot. Motor test for S1 was to test plantar flexion and eversion of the foot by opposing this motion with pressure on the head of the fifth metatarsal. There is no reflex to test for L5 function, but S1 was tested with the Achilles tendon reflex. Sensation for L5 was tested on the dorsum of the foot; sensation for S1 was tested at the lateral malleolus. In addition to the L5 and S1 nerve roots, major peripheral nerves tested included the superior and inferior gluteal nerves, as well as the sciatic, tibial and common