Although nonspecific low-back pain is a highly prevalent condition, its clinical course over time remains uncertain. A large-scale meta-analysis of available research suggests that seeking treatment sooner rather than later can be important for pain relief and reduced disability; however, residual effects still may linger for a year or longer.
A research team at the University of Sydney, Australia, systematically reviewed studies investigating the clinical time course, or prognosis, of pain and disability in patients with either nonspecific acute or persistent low-back pain [Costa et al. 2012]. In a meta-analysis, they included only prospective studies that measured back pain, disability, or a global measure of recovery.
Reported in an advance online edition of the journal of the Canadian Medical Association (CMAJ), data from 33 discrete cohorts of patients (11,166 total participants) were included in the review and analysis.
- Acute low-back pain was defined as pain having lasted less than 12 weeks at the time patients entered the respective research studies. In these groups, the mean pain score (out of 10 maximum) was 5.2 at baseline, 2.3 at 6 weeks, 1.2 at 26 weeks, and 0.6 at 52 weeks after the onset of pain.
- Persistent low-back pain was of >12 weeks but <12 months in duration at the time of study entry. In these groups, the mean pain score (out of 10) was 5.1 at baseline, 3.3 at 6 weeks, 2.6 at 26 weeks, and 2.3 at 52 weeks after the onset of pain.
As for disability, the course of outcomes on this measure was similar to pain outcomes over time in the acute pain groups, but disability outcomes were slightly better than pain outcomes over time in persons with persistent low-back pain. Recovery was achieved by a majority of patients with acute pain by 12 weeks in the 19 studies that assessed this measure; however, among patients with persistent low back pain, less than half had recovered fully by one year.
The authors conclude that patients developing either acute or persistent low-back pain improve most dramatically within the first 6 weeks. After that time, improvement slows and low-to-moderate levels of pain and disability may still be present at one year, especially in patients that had pain longer prior to seeking treatment (ie, persistent pain).
COMMENTARY: This was a large-scale meta-analysis on a topic of great importance. Roughly 80% to 90% of the population experiences back pain at some point in their lives, with about a quarter reporting such pain during any given week.
This study’s findings suggest that all patients seeking care for low-back pain may improve most rapidly within the first 6 weeks. A further implication is that many of the apparent benefits in terms of reduced pain and disability may be unrelated to the type of intervention; however, the researchers did not report specifics on the exact nature of back pain or the treatments that were studied in the various trials.
Average, or mean, pain scores were moderate at baseline (roughly 5 on a 10-point scale), so it is unknown if improvements would be greater and of more clinical significance if the initial pain is more severe. However, it was clear in this meta-analysis that patients receiving care earlier in the course of low-back pain achieved more rapid and enduring benefits.
Still, mean scores can be somewhat deceiving. There was a moderate degree of person-to-person variability, with a standard deviation of 2 points on 10-point pain or disability scales; that is, nearly a third of individual patients could have scores that differ by more than 2 points — higher or lower — from group means reported in the study. There also was a moderate to high amount of heterogeneity among studies that might have skewed meta-analysis results.
Another possible explanation of improvements in pain and disability, as duly noted by the researchers, is regression to the mean, whereby individual scores trend toward group averages over time independently of treatment effects. A contributor to this phenomenon is random variation over time, as the researchers explain…
“Some of the randomness will be ‘true’ variation caused by biological, psychological or sociological mechanisms (e.g., people’s pain will fluctuate unpredictably because of their activity levels and mood) and some will be measurement error (because people’s self-reports of their pain and disability will not be perfectly precise). It is probably impossible to properly partition out the contributions of these two sources of regression to the mean.”
Costa and colleagues believe that, despite the possibility of this confounding effect, their findings are of pragmatic value because the scores still represent self-reported reductions in pain and disability over time; even though the exact cause of the improvements may not be known.
The message for patients seems to be that they should seek care for nonspecific low-back pain soon after its development to help shorten recovery time and minimize long-term adverse effects. Realistically, however, even at one year all persons with nonspecific low-back pain may still experience some residual discomfort and disability, and patients should be educated on this possibility.
REFERENCE: Costa LCM, Maher CG, Hancock MJ, et al. The prognosis of acute and persistent low-back pain: A meta-analysis. CAMJ. 2012; online ahead of print [abstract here].
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