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While some guidelines recommend two diagnostic nerve blocks before radiofrequency treatment for chronic low back pain, a randomized trial showed greater success without use of the prior blocks.

The randomized, multicenter study conducted among 151 patients with chronic low back pain, also showed that eliminating the diagnostic nerve blocks substantially reduced costs, according to Steven P. Cohen, MD, of Johns Hopkins in Baltimore and colleagues.

Writing in the August issue of Anesthesiology, Cohen and colleagues determined the comparative costs (P<0.001) of successful radiofrequency denervation with and without preceding facet joint nerve blocks to be:

• No prior screening block, $6,286
• A single diagnostic block, $17,142
• Two confirmatory blocks, $15,241

Numerous organizations and guidelines have advocated the double-block paradigm for the confirmatory diagnosis of lumbar facet arthropathy, but diagnostic spinal injections can be inaccurate and associated with false-negative responses, the researchers wrote.

And although official guidelines have advocated the double-block standard, several randomized trials suggested that single blocks might suffice.

Furthermore, diagnostic blocks are not without serious complications, such as neuraxial infection, while increasing concerns about cost-effectiveness have added to a growing controversy about the need for confirmatory blocks.

To explore both efficacy and cost-effectiveness, Cohen and colleagues randomized 151 patients with chronic low back pain, with the endpoints of cost and "successful outcome" -- which consisted of a 50% or more reduction in pain and a positive global perceived effect that persisted for three months or more.

Most patients were in their 40s, and men predominated. Median duration of symptoms was three to four years.

The first diagnostic block was positive in 40% of patients in the single-block group and in 58% of those in the double-block group.

Among responders to the first block, pain relief was substantial, at 77.5% and 75% in the single- and double-block groups, respectively.

In the double-block group, 48% had a positive second block.

Denervation success rates were 33% in the no-block group, 39% in the single-block group, and 64% in the double-block group.

The proportion of successful outcomes was highest in the group that had no screening blocks, with 58.8% at one month and 33.3% at three months.

In contrast, successful outcomes at those time points were seen for 26% and 16% in the single-block group and 22.5% and 22% of those in the double-block group (P<0.001).

"Our results suggest that the current controversy surrounding whether single or double blocks are superior may be misguided. Instead, the operative question may be whether any blocks should be done before lumbar z-joint denervation," the researchers wrote.

However, they cautioned against the abandonment of diagnostic blocks altogether, because many of the responders in the no-block group were likely to have been placebo responders.

Moreover, the investigators noted, "The current reimbursement paradigm for facet interventions is an artificial construct incommensurable with that for other spinal interventions (e.g., spinal fusions, decompression surgeries), wherein the diagnostic procedure generally is reimbursed only a small fraction of the 'definitive' treatment."

They also noted that the study had its flaws, including a lack of blinding and placebo control, as well as the three-month cutoff for response.

Their findings also might be affected by changes in reimbursement. "The conclusions drawn today might differ from those drawn tomorrow, contingent on decisions from third-party payers."

In an accompanying editorial in the same issue of Anesthesiology, Jan Van Zundert, MD, PhD, of Maastricht University in the Netherlands, and colleagues, wrote, "The design and findings of this study provide an important contribution to the ongoing debate on patient selection and the so-called diagnostic blocks."

But an important and, as-yet unaddressed, problem is the lack of a definitive standard on how diagnostic blocks should be performed -- with wide variations being seen in patient selection, technique, medications used, and doses, Van Zundert and colleagues pointed out.

"Standardization and scientific validation of (controlled) diagnostic medical branch blocks is highly needed to identify its real value in clinical practice," the editorialists wrote.