Lumbar Epidural Injection
Epidural steroid injections are one of the most commonly performed procedures in pain medicine. Although they have historically been utilized for spinal pain of all types, they are widely acknowledged to work better for neuropathic pain. Yet, there continues to be enormous controversy surrounding the short and long-term efficacy, effectiveness, and, more recently, safety of this treatment.
Mechanisms of action
The mechanisms by which steroids exert their analgesic effects have been debated for many years. Corticosteroids inhibit the enzyme phospholipase A2, an inflammatory mediator present in elevated concentrations in herniated and degenerative intervertebral discs, but its main role is as the rate-limiting factor involved in the production of arachidonic acid, which is the principal substrate for the cyclo-oxygenase and lipo-oxygenase pathways. Metabolism by these pathways results in the formation of the four different classes of eicosanoids: prostaglandins, prostacyclins, thromboxanes, and leukotrienes. Prostaglandins, along with these other arachidonic acid byproducts, can cause or exacerbate pain via their inflammatory effects and ability to sensitize peripheral nociceptors. In addition to their anti inflammatory effects, steroids may inhibit pain via their ability to suppress ectopic discharges from injured nerve fibers and depress conduction in normal unmyelinated C fibers.
Several proposed mechanisms for the beneficial effects do not involve steroids. The injection of local anesthetic can increase blood flow to ischemic nerve roots and, similar to steroids, suppress ectopic discharges from injured neurons and slow or halt nociceptive transmission. Moreover, the administration of saline, local anesthetic, or any non-steroid solution can exert an analgesic effect via the washout of inflammatory cytokines and the adhesiolysis of scar tissue.