Rationale: How, When, and Why to Use Epidural Corticosteroid Injections
There is an ongoing trend towards non-surgical management of disc herniations with or without radiculopathy. Evidence to support this trend includes observation of non-operative resorption of lumbar herniated disc material, disc induced low back or radicular pain in the absence of frank herniation, and the common occurrence of asymptomatic disc herniations through formal imaging studies in a normal population (1, 18).
A complex interaction between biochemical inflammatory mediators from the damaged disc and mechanical factors including frank compression may lead to a painful radiculopathy. Vascular insufficiency with hypoxic injury to the nerve root may also be present. Epidural steroids are administered into the spinal canal in the space outside of the thecal sac which contains the nerve roots. This location is adjacent to the most common site of contributing pathology, the herniated disc, which may cause this mechanical deformation of the nerve roots with a significant inflammatory reaction. Studies have shown that phospholipase A2 (PLA2), cytokines, and other inflammatory mediators are released front an intact disc following injury (15). PLA2 is highly inflammatogenic and propagates an inflammatory cascade with the liberation of arachidonic with inflammatory responses via leukotrienes and prostaglandins.
This chemical, inflammatory cascade then becomes the target for NSAIDs or corticosteroids (oral or epidural) which can inhibit prostaglandin synthesis. Epidural corticosteroids also act by blocking PLA2 activity and can exert an "anesthetic" like action blocking nociceptive C-fiber conduction (10). There is also a membrane stabilizing effect from the epidural corticosteroids, which may help decreased ectopic neuronal discharges and thus decrease radicular pain (6). Various studies also provide a rationale for the use of anesthetics in a routine epidural injection. Postulated mechanisms include an interruption of both the pain-spasm cycle and the reverberating nociceptive transmission, as well as a presumed action through a hydrostatic (mechanical) effect. There is also the obvious benefit of disruption of afferent sensory impulses with pain reduction, thus confirming which are the symptomatic nerve roots. Patients may also have the psychological benefit from experiencing some relief of symptoms, even if only short lasting.
The most recent study on epidural steroids, published in the New England Journal of Medicine in 1997, was a randomized, controlled, double-blind trial involving adults with greater than I month but less than one year of sciatica with CT evidence of a herniated disc (4). The patients treated with epidural methylprednisolone acetate (80mg in 8ml of normal saline) showed short-term improvement in pain control and sensory deficits compared with epidural normal saline. The differences between treatment and control groups faded over time leading Carette, the chief author, to conclude that ESIs offer no long-term benefit in function or need for surgical intervention. However, one of the major drawbacks of this study was that there were no structured co-interventions, thus making the epidural function the sole intervention and not a therapeutic modality incorporated into a comprehensive rehabilitation and treatment armamentarium. Additional study limitations included the lack of fluoroscopic guidance, 3-month follow up only, and the mean duration of symptoms being 13 weeks, thus failing to study patients with acute radiculopathy. It is the author’s opinion that epidurals should never be utilized as a treatment in isolation, and that earlier intervention is more efficacious and more likely to result in a more rapid recovery with a decrease in subsequent surgeries.
Another well-designed retrospective study of 54 patients with lumbar radiculopathy proven by electromyogram (EMG) due to a herniated lumbar intervertebral disc was completed by Saal et al (14) in 1989. Patients had back school, "stabilization exercises", aerobic and flexibility exercises, oral medications, and EST’s "when indicated for pain control". 90% of these patients had a good to excellent outcome with a 92% return-to-work rate. This study demonstrated that lumbar intervertebral disc herniations with radiculopathy can be treated very successfully with aggressive non-operative care, which includes epidural steroid injections.