Is Procedural Pain Prognostic in Lumbar Epidural Injection?

Kate Johnson

February 27, 2012

February 27, 2012 (Palm Springs, California) — Concordant pain provoked during lumbar epidural steroid injection (LESI) for radicular pain seems to be predictive of improved pain relief at 6 months postprocedure, Kenneth D. Candido, MD, and colleagues reported here at the American Academy of Pain Medicine (AAPM) 28th Annual Meeting.

Another study presented at the same meeting showed very different findings with LESI.

The disparity between the 2 studies' results makes it clear that there are distinct differences between different LESI approaches, said Dr. Candido, who is chairman and professor in the Department of Anesthesiology at Advocate Illinois Masonic Medical Center in Chicago.

"We're looking at an interlaminar approach, and the other investigators are looking at a double-injection transforaminal technique," he said in an interview with Medscape Medical News.

"What is substantiated by [the other] study is that the transforaminal technique does not reliably place the medication into the ventral compartment where the pain generators are located, and that's borne out by their results," he said. "In fact, what they've actually done is complementary. They've enhanced our paper substantially."

When LESI is performed in patients with unilateral radicular lumbosacral pain resulting from disk herniation or degeneration, the procedure can produce pain (pressure paresthesia) that either reproduces the patient's dermatomal leg pain (ipsilateral, or concordant, pain) or occurs in a different distribution to their leg pain (contralateral, or discordant, pain), Dr. Candido noted.

It has been hypothesized that the provocation of concordant pain might indicate the successful targeting of medication, he said.

"If we can stimulate a nerve or series of nerves that are irritated, that are angry, that are inflamed, it implies we've hit the target of what's causing that patient's usual, customary, and daily pain, and by and large, we would suspect that the success rate would be longer," he explained.

Researchers involved with the second study were working from the same hypothesis.

"We thought that concordant provocation could be predictive of clinical outcomes," said lead investigator Eric Kim, MD, from New York University School of Medicine in New York City. "But in our study, it's not predictive of clinical outcome. We actually didn't show a statistically significant difference between concordant and discordant provocation."

Dr. Kim and colleagues followed 47 patients, mean age 48 years, who received fluoroscopically guided LESI, using a transforaminal approach. Participants received 80 mg methylprednisolone acetate (DepoMedrol, Pharmacia) and 1 cc of 0.25% bupivacaine at 2 separate levels.

The primary outcome measure was self-rated percentage of pain reduction from baseline to follow-up. Secondary outcome measures were differences in activity level and daily analgesic consumption.

Injection-related pain provocation occurred in 100% of the cohort — concordantly in 66% and discordantly in 34% — Dr. Kim reported.

At 2 to 3 weeks postinjection, contrary to their hypothesis, the discordant pain group achieved a greater decrease in self-reported pain from baseline to follow-up compared with the concordant pain group (76% vs 58%; P < .04).

"They all had improvement from preinjection to postinjection follow-up," he told Medscape Medical News. "In the concordant group, 20 out of 31 (64%) had greater than 50% reduction in pain, vs 15 out of 16 (94%) in the discordant group. But there was no statistically significant difference between the groups."

The reason likely lies in where the medication goes, said Dr. Candido.

"We have shown previously that the medication gets to the ventral epidural space only 75% of the time when you do a transforaminal technique (others have reported 90% [drug delivery with the transforaminal technique]) compared with 100% ventral epidural spread using an interlaminar parasagittal approach," he said ( Anesth Analg. 2008;106:638-644).

"That translates now for the first time to improved analgesia," Dr. Candido announced. Even the interlaminar midline approach is inferior to the parasagittal approach, he added.

"A parasagittal technique drives the medication ipsilaterally: If you inject using a conventional, midline interlaminar injection, medication is going to spread to the right and to the left, meaning some of the medication will go to the concordant side, where the pain is originating from, and some will not, which is therefore a waste of some precious analgesic drug," he pointed out.

In his study, 44 patients were randomly assigned to undergo LESI using either a midline approach or a parasagittal interlaminar approach. All patients received 120 mg (2 mL) methylprednisolone acetate, along with 1 mL normal saline solution and 1 mL lidocaine 1%.

Injection-related pain was provoked in 100% of the parasagittal group, but only 28% of the midline group.

Concordant (ipsilateral) pain was reported in 68% (15/22 patients) of the parasagittal group and 18% (4/22 patients) of the midline group, whereas discordant (contralateral) pain was reported in 32% (7/22 patients) of the parasagittal group and 20% (1/5 patients) of the midline group.

A highly significant difference in the rate of moderate-to-severe paresthesias was also found (82% parasagittal vs 14% midline; P < .001).

In a 6-month follow-up of these patients, reported earlier by Medscape Medical News, Dr. Candido noted that the parasagittal approach, with its predominance for concordant procedural pain, resulted in significantly better long-term analgesia compared with the midline approach.

Although both groups showed improvement in Oswestry Low Back Pain scores from baseline, these improvements were statistically significant only in the parasagittal group (P = .037).

Similarly, both groups experienced statistically significant improvements in resting numeric rating scores on days 1, 7, and 28 after treatment. However, this improvement was more pronounced in the parasagittal group, both at rest (P = .026 vs P = .044) and with movement (P = .005 vs P = .019).

Rather than challenging these results, the study by Dr. Kim and colleagues indirectly strengthens them, Dr. Candido asserted.

"In fact, their study actually corroborates what we've been saying all along, that they're not getting the medicine to the target to the degree that we are."

Dr. Candido and Dr. Kim have disclosed no relevant financial relationships.

American Academy of Pain Medicine (AAPM) 28th Annual Meeting: Abstracts 130 and 143. Presented February 23, 2012.

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