Predicting Outcome after Epidural Steroid Injection
Abstract & Commentary
By Michael Rubin, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Rubin reports no financial relationships relevant to this field of study.
Synopsis: Response to treatment of unilateral lumbar radiculopathy can be predicted by an abnormal needle EMG in the appropriate root distribution.
Source: Annaswamy TM, et al. Needle electromyography predicts outcome after lumbar epidural steroid injection. Muscle Nerve 2011: 10 OCT 2011 11:07AM EST | DOI:10.1002/mus.22320
Can needle electromyography (EMG) be used as an independent predictor of beneficial outcome to epidural steroid injection in patients with lumbosacral radiculopathy? To address this question, 89 patients with lumbosacral radiculopathy, 79 men and 10 women, were consecutively enrolled in this hospital-based, outpatient, prospective study. Lumbosacral radiculopathy was defined as either: (A) radiating pain in an L4, L5, or S1 nerve root distribution, (B) motor, sensory, or deep tendon reflex abnormalities on neurological examination in an L4, L5, or S1 nerve root distribution, or (C) magnetic resonance imaging evidence of L4, L5, or S1 nerve root impingement. Exclusionary criteria included pregnancy, anticoagulation, allergy to steroids or bupivicaine, homelessness, and the inability to travel to appointments or converse in English. All patients underwent intralaminar steroid and bupivicaine injection under fluoroscopic guidance, with needle placement confirmed using contrast dye. The primary objective was to determine if an abnormal EMG, indicative of lumbosacral radiculopathy and defined as positive waves or fibrillation potentials in a myotomal distribution, predicted pain relief from epidural steroid injection. Secondary objectives assessed whether other factors were predictive of pain relief following epidural steroid injection, including age, sex, smoking history, work status, body mass index, self-rating pain disability questionnaires encompassing psychosocial and functional disability sub-scores, and alcohol use. Statistical analysis included post-hoc Tukey multiple comparisons and simple linear regression.
Of 89 enrollees, 19 dropped out due to non-compliance (n = 11), refusal to continue or discovery of alternate diagnosis (n = 3 each), and spontaneous improvement or relocation to another facility (n = 1 each). All enrollees fulfilled either the history or examination criteria for lumbosacral radiculopathy, or both. MRI was never the sole criteria for study inclusion. EMG data were available and complete for 80 subjects, of which 42 were indicative of lumbosacral radiculopathy, 25 were normal, and 13 were equivocal. Of these 80, a first epidural steroid injection was performed on 78, and a second was performed on 43, either before or after a follow-up visit that occurred, on average, 126 days later. Significantly greater improvement was found in the abnormal EMG group, compared to the normal EMG group, in patient disability pain questionnaire scores, in both its psychosocial and functional sub-scores, and in the numerical rating pain scale. Abnormal needle EMG findings of lumbosacral radiculopathy is an independent predictor of and can identify those patients more likely to benefit from epidural steroid injection.
Commentary
Is interlaminar epidural injection, depositing steroids in the posterior epidural space, or transforaminal epidural injection, depositing steroids in the anterior epidural space, the favored route for unilateral radicular pain? Usually, half the dose of steroid is used in the latter method compared to the former. Among 64 chronic radiculopathy patients treated in a randomized, prospective study, both methods were equally efficacious, 39% and 38% respectively, in providing significant improvement over a 6-month period, as measured by visual analog scale pain scores and functional capacity using the Owestry scale.1 Apparently, epidural injection may work from either approach.
Reference
1. Rados I, et al. Efficacy of interlaminar vs transforaminal epidural steroid injection for the treatment of chronic unilateral radicular pain: Prospective, randomized study. Pain Med 2011;12:1316-1321.
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