Can patient characteristics predict benefit from epidural corticosteroid injections for lumbar spinal stenosis symptoms?

Background context Epidural corticosteroid injections are commonly used to treat back and leg pain associated with lumbar spinal stenosis. However, little is known about which patient characteristics may predict favorable responses. Purpose The aim was to identify patient characteristics associated with benefits from epidural injections of corticosteroid with lidocaine versus epidural injections of lidocaine only for lumbar spinal stenosis symptoms. Study design/setting This was a secondary analysis of Lumbar Epidural steroid injections for Spinal Stenosis randomized controlled trial data from 16 US clinical sites. Patient sample Patients aged older than or equal to 50 years with moderate-to-severe leg pain and lumbar central spinal stenosis randomized to epidural injections of corticosteroids with lidocaine (n=200) or lidocaine only (n=200) were included. Outcome measures Primary outcomes were the Roland-Morris Disability Questionnaire (RMDQ) and 0 to 10 leg pain intensity ratings. Secondary outcomes included the Brief Pain Inventory Interference Scale and the Swiss Spinal Stenosis Questionnaire. Methods At baseline, clinicians rated severity of patient spinal stenosis, and patients completed predictor and outcome measures. Patients completed outcome measures again 3 and 6 (primary end point) weeks after randomization/initial injection. Analysis of covariance was used with treatment by covariate interactions to identify baseline predictors of greater benefit from corticosteroid+lidocaine versus lidocaine alone. We also identified nonspecific (independent of treatment) predictors of outcomes. Results Among 21 candidate predictors and six outcomes, only one baseline variable predicted greater benefit from corticosteroid+lidocaine versus lidocaine only at 3 or 6 weeks. Compared with patients who rated their health-related quality of life as high on the EQ-5D Index, patients who rated it as poor had greater improvement with corticosteroid than with lidocaine only in leg pain at 6 (but not 3) weeks (interaction coefficient=2.94; 95% confidence interval [CI]=0.11-5.76; p=.04) and in RMDQ disability scores at 3 (but not 6) weeks (interaction coefficient=4.77, 95% CI= -0.04 to 9.59; p =.05). Several baseline patient characteristics predicted outcomes regardless of treatment assignment. Conclusions Among 21 baseline patient characteristics examined, none, including clinician-rated spinal stenosis severity, were consistent predictors of benefit from epidural injections of lidocaine+corticosteroid versus lidocaine only.