Low back pain of a radicular nature can have a variety of causes.

• Annular tear (lumbar sprain).
• degenerative disk disease.
• herniated nucleus pulposis with nerve root irritation or compression with or without neuralgic deficit.
• spondylolisthesis, facet arthropathy with compromise of a neuroforamin
• spinal stenosis, or recurrence of pain post laminectomy.

The underlying mechanism remains nerve root irritation. It is well documented that a herniated disk can cause nerve root inflammation either from "irritative" effects manifesting as sciatica or from "compressive" lesions characterized by sensory, motor, or reflex disturbances.

Clinical improvement after epidural steroid injection coincides with decreased nerve root edema.

A possible mechanism of steroid action reflects inhibition of Phospholipase A2 resulting in decreased synthesis of prostaglandine.
The steroid preparation most commonly used is methylprednisolone acetate (Depo-medrol). Other steroid preparations used include triamcinolone diacetate (Aristocort). For lumbar epidural injections the steroid preparation is often diluted with local anesthetic to a 6 ml - 10 ml volume to allow spread to adjacent nerve roots which may be inflamed as well. The use of a dilute local anesthetic is often beneficial in patients with coexisting myofacial pain, and can act as a marker of correct deposition of medication with the onset of sensory blockade. Absolute contraindications to central nerve block include coagulopathy, systemic anticoagulation, sepsis or local infection at the site of needle insertion.

A thorough diagnostic workout is essential prior to treatment with epidural steroids. When the history, physical, and neurological examination indicate radicular pain, imaging studies such as MRI should be considered. If motor weakness or dense sensory loss is occurring, neurosurgical evaluation is indicated. Subtle nerve deficits can often be evaluated by EMG while structural changes such as facet hypertrophy are more readily evaluated by CT. Often, patients present with a complex problem involving more than a single lesion (for example, a patient may have a herniated disk as well as facet joint hypertrophy and diffuse myofacial pain). These patients are most appropriately treated in a comprehensive setting.

The effectiveness of epidural steroid injections often depends on the etiology of the nerve root irritation as well as its duration. Radiculopathies of a six-month duration or less have an overall response rate to epidural steroid injection of 60-70%. Patients who present with pain of over a year duration have a response rate of 40-50%. The few studies available looking at long term results show a recurrence of pain in 50% of responders after twelve months. The etiology of the lesion may have a role to play in this. Pain related to a herniated disk or disk bulge often responds well while pain related to structural lesions such as spondylolysis, spondylolisthesis, scoliosis or spinal stenosis have poorer response rates. This may be due to nerve fibrosis secondary to prolonged or recurrent inflammation of many years duration. Even in cases of spinal stenosis if an acute radiculopathy develops it may be treated as if it were a new lesion, often with good response rates. Recurrence of pain postlaminectomy may be treated in a similar fashion. Radicular pain in a new distribution or pain recurring after a significant period of relief may be amenable to epidural steroids. Postlaminectomy pain related to scarring around nerve roots or facet joints may benefit from alternate approaches such as facet joint nerve blocks or epiduraloscopy with lysis of adhesions. Patients who have undergone multiple back surgeries, who develop arachnoiditis, or other patients with intractable low back pain may be considered for spinal cord stimulation or other implantable technologies when more conservative approaches fail.

The approach taken with an epidural steroid injection can influence the overall response. Should a standard approach fail to give good results better responses can often be obtained with a transforaminal approach under x-ray guidance. This is accomplished by depositing medication closer to the area of injury. Variations of the technique can also be used to help diagnose an involved nerve root when multiple sites are suspected.

Epidural steroid injections are also effective for other diagnoses. Recovery is often hastened in patients who have suffered an annular tear (lumbar sprain). Patients who develop an acute varicella zoster virus infection (shingles) deserve special attention. In addition to antiviral agents which limit the duration of illness, tricyclic antidepressants with or without narcotics and topical local anesthetics can relieve pain. An epidural steroid injection should be considered in patients over age fifty who are more prone to developing post herpetic neuralgia. For a patient who develops a vertebral compression fracture oral narcotics are often indicated. Paravertebral injections may decrease pain acutely. Should pain recur after the vertebra has healed an epidural steroid injection can often provide long-term pain relief.

The most benefit from an epidural steroid injection occurs when a comprehensive approach is utilized. An emphasis on return to function as well as pain relief is essential. Pharmacological interventions and nerve blocks (such as epidural steroid injections) are a good first step. Long-term improvement can often be obtained when epidural steroid injections are followed by appropriate forms of therapy with an emphasis on body mechanics and proper pacing. Physical therapy, occupational therapy, aquatic therapy and work hardening are available as worksite evaluations. In some cases weight loss directed by a nutritionist can have a significant impact. Psychological support is also appropriate for some patients suffering from chronic pain. Coordination of efforts to obtain optimum results is most appropriately performed in a comprehensive pain management clinic.
 
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