The question of when do epidural steroids work for low back pain is complicated. Not all types of back pain are responsive to epidural steroids. Back pain can be radicular, meaning that it is due to nerve root irritation from a bulging or herniated disc. Back pain can also be axial, meaning that there is no radiation into the legs. This may be due to disease in the facet joints of the spine. Muscle spasm and sacroiliac joint disease may also produce pain in the back which is similar to the above two mechanisms.
Additionally, an epidural steroid injection may be administered in several ways. These include caudal ( at the bottom of the spine), interlaminar ( through the midline of the back), and transforaminal ( through the hole which the nerve root exits). Each of these methods target a particular area of the spinal chord and nerves and may be specific for a certain set of symptoms.
The studies analyzing the efficacy of epidural steroid injections are complicated by the previously discussed issues. Many studies do in fact find that there are improvements in the severity of pain from epidural steroid injections, especially in the short term. Additionally, different types of steroids may be injected into the epidural space. These including particulate steroids versus non-particulate steroids. There are some suggestions that particulate steroids may be more effective than non-particulate steroids. Particulate steroids, however, come at an additional risk over non-particulate steroids. These additional risks must be weighed against the benefits.
Additionally, the issue of multiple epidural steroid containing injections must be addressed. There are several studies suggesting that additional (more than one) injections may provide a synergistic effect on pain relief. Many providers limit the number of injections containing a steroid to three within a six month period. The injection of steroids is not without risk, including elevated blood sugar, weight gain, muscle weakness and other issues. The performance of multiple injections must be weighed against their additive risk.
Finally, in spite of conflicting evidence, there are some conclusions that we can draw. In general, epidural steroid injections are effective for decreasing radicular pain due to bulging or herniated discs. Epidural steroid injections are also effective for reducing pain due to spinal stenosis, a narrowing of the bony spinal canal. There are other non-invasive modalities that may be useful including physical therapy and non-steroidal anti-inflammatory medications. The risks and benefits of any intervention should be discussed with your pain management provider and an individualized protocol should be designed for each patient.