Dr. Cousins and Drs. Aldrete and Ghaly raise several important issues. I agree with Dr. Cousins’s suggestion about using the “numbers needed to treat” approach as a statistical tool to assess outcomes after epidural steroid injections. The problem remains that many of the existing studies in which such an approach could be applied are methodologically flawed. 1Recent efforts to organize a large, methodologically sound, randomized study have been unsuccessful. One such project was organized through the Pain Outcomes Research Group of the American Society of Regional Anesthesia and Pain Medicine, Richmond, Virginia. The principal reason for the failure of that project was that referring surgeons were reluctant to enroll their patients into such studies because they were convinced of the effectiveness of epidural steroid injections and did not wish to delay effective therapy for those patients who would serve as controls. Perhaps such a study could be organized in a country in which the use of epidural steroid injections is not as widely accepted.
I very much appreciate Dr. Cousins’s comments about the potential for harm from occlusion of small-end arteries by steroid suspensions. Methylprednisolone acetate tends to form aggregates of the steroid material when mixed with local anesthetic and may pose more of a risk for this problem than methylprednisolone acetate; but I suspect either preparation could produce devastating consequences if injected into a spinal artery. An animal model for this type of injury could possibly be developed.
I agree with the comments of Drs. Aldrete and Ghaly that it would be ideal to have a definitive diagnosis before initiation of epidural steroid injections. For patients who underwent previous spine surgery or who have a complicated or atypical medical history, imaging studies should certainly be performed before an injection. However, we often see patients whose history and physical findings are very typical of disk herniation and radiculopathy and who appear to be ideal epidural steroid candidates. In that situation, the principle reason to perform magnetic resonance imaging is to rule out a rare alternate cause of symptoms because there is poor correlation between imaging results and response to epidural steroids. 2Is it worth performing a $1,500.00 study to rule out a condition with an incidence of 1 in 10,000 or 1 in 100,000? I am aware of only one case in which bleeding occurred after an epidural steroid injection in a patient with an intraspinal tumor. In that case, the lesion was misdiagnosed after myelography as disc herniation.
I disagree with Aldrete and Ghaly’s comments about the diagram in figure 1. Their statement that the condition illustrated (mechanical compression of the nerve root) is likely to end up in surgery is probably true. However, Pawl 3studied the effects of epidural steroid injections among patients who had been preselected as surgical candidates and who had signs of nerve root compression. He found that 50% of patients with cervical radiculopathy and 35% of patients with lumbar radiculopathy sufficiently benefitted from epidural steroids to avoid surgery.
The statement by Aldrete and Ghaly that dural puncture is more likely to occur if injection is done at the level of disc herniation is unfounded. As shown by Hogan, 4there is a segmentally occurring pyramidal space occupied by epidural fat that lies beneath the ligamanta flava. This rather generous space, into which the needle passes during a midline approach, would not be distorted by disc herniation. Most authors, including myself, recommend injecting the steroid as closely as possible to the level of the affected nerve root.
Aldrete and Ghaly state that triamcinolone diacetate (Aristocort Forte and Aristocort Intralesional; Fujisawa, Deerfield, IL) and methylprednisolone acetate (Depo-Medrol; Pharmacia & Upjohn, Bridgewater, NJ) contain benzyl alcohol and polyethylene glycol, both of which are neurotoxic. I know of no study that has shown neurotoxicity of these preparations or of the components of the vehicle in the concentrations found in the commercial preparations. As Drs. Aldrete and Ghaly point out subsequently, both of these preparations have been shown to be devoid of adverse effects when administered intrathecally or epidurally in animals. 5,6
Unlike Aldrete and Ghaly, I would continue to urge caution when considering intrathecal injections of corticosteroids. My series of intrathecal steroid injections7 was not devoid of adverse effects, as these authors suggested. There were several patients in whom transient symptoms developed compatible with a diagnosis of aseptic meningitis. Although I do not believe there is a high risk for the development of arachnoiditis, the literature regarding the use of repeated epidural steroid injections in patients with multiple sclerosis raises some concerns.