Wednesday, December 26, 2012

Smoking & Back Pain: What’s The Connection?

In The NewsThe possible relationship between tobacco smoking and pain is complex and research on this subject often has been confusing. A new study, widely reported in news media, claims that smoking cessation can be important for aiding patients with back pain disorders. While this seems sensible, the outcomes of the study were not as strong and unambiguous as news reports implied.

Caleb Behrend, MD, at the University of Rochester, New York, and colleagues conducted a cross-sectional study to examine the effects of tobacco smoking versus smoking cessation on pain and disability in 5,333 patients with painful spinal disorders [Behrend et al. 2012]. Data for the study came from a medical records database at two academic hospital centers where the selected patients were receiving care for back pain disorders, either focused on the spine (axial) or also involving the legs (radicular).

The researchers extracted data regarding smoking history and patient assessments of pain on 4 visual analog scales (VAS) during the course of care — evaluating (1) worst, (2) least, (3) weekly average, and (4) current pain. During the study, patients were treated with physical therapy, over-the-counter pain relievers, a home exercise program, injections, and/or surgery. The average duration of follow-up was 8 months.

Writing in the Journal of Bone & Joint Surgery, the researchers report that compared with patients who had never smoked, those who were current smokers reported significantly greater pain on all 4 VAS ratings (P<0.001) at the time of entry into care for back pain. Subsequently, during the course of care, the average improvement in reported pain was significantly less among current smokers versus nonsmokers (P<0.001).

Furthermore, compared with patients who continued to smoke, those who quit smoking during the course of care reported significantly greater improvements in VAS pain ratings for worst (P=0.013), current (P<0.05), and weekly pain (P=0.024). As a group, the researchers observe, patients who had continued smoking throughout treatment had no clinically important improvements in reported pain; whereas, many of those who never smoked or discontinued smoking at some point did have meaningful pain relief.

Given the strong association between improved patient-reported pain and smoking cessation, the researchers believe that their data support the need for smoking cessation programs for all patients with painful spinal disorders.

COMMENTARY: Unquestionably, for many health reasons, smoking cessation could be important for patients with any type of pain disorder. This present study appears to support that contention when it comes to back pain; although, somewhat moderately so and it leaves some important questions unanswered.

As we have often noted in these UPDATES, P-values denoting statistically significant differences are not a very desciptive measure of effectiveness. According to our own calculations from study data, there was a mean 20% improvement from baseline to followup in VAS worst pain scores among non-smokers compared with a mean 9% improvement on this measure in smokers, or Standardized Mean Difference effect sizes of 0.44 and 0.23, respectively. For current pain, comparable improvements were 21% (SMD=0.31) and 8% (SMD=0.15) in non-smokers and smokers, respectively. Therefore, effect sizes were only moderate for pain improvement associated with non-smoking, but generally small and clinically marginal among smokers.

Furthermore, the researchers claim that a decrease in VAS pain rating of >30% distinguishes clinically important differences, with patients reporting that symptoms are somewhat or much improved at that level. As noted above, however, the overall mean-percentage improvements in worst and current pain as a result of treatment did not reach that level among either non-smokers or smokers (and there were similar trends for least and weekly pain measures on VAS).

Still, in terms of absolute numbers, the researcher reported the percentage of patients reporting a >30% decrease in worst pain for each of the 4 groups as follows: a) patients who had never smoked — 31.2%; b) prior smokers — 29.1; c) those who quit smoking during the study — 32.0%; and, c) current smokers — 16.6%. So, while less than a third of non-smokers achieved meaningful levels of pain relief, this was nearly double those who continued to smoke.

The researchers also had assessed changes for each group on the Oswestry Disability Index (ODI), and these scores differed significantly for those who had never smoked and current smokers (P<0.05). As a result of treatment for back pain, greater mean improvement on the ODI was observed in patients who had never smoked (-7.3 points; 95% confidence interval, -8.1 to -6.5 points) compared with current smokers (-4.6 points; 95% CI,-5.6 to-3.6 points). However, none of the changes on this measure were of a size considered to be clinically important.

It is curious that during the 8 months of followup continuing smokers had only small and clinically unimportant improvements in pain. Were the detrimental effects of smoking prominent enough to largely overpower any beneficial effects of therapy? However, at the same time in this particular study, even improvements among non-smokers were not of large and impressive proportions.

Behrend et al. concede that a weakness of their study was in not being able to assess the types of medical interventions for pain in the various groups, or the influences of individual patient factors (other than smoking). For example, is it possible that smokers were provided a different range of therapies for their back-pain conditions than non-smokers? Or, that more non-smokers had generally healthier lifestyles — eg, diet, exercise, etc. — which may have affected their outcomes?

Answers to such questions could be important, so that practitioners and patients can have realistic expectations as to the influence of smoking and smoking cessation on the persistence or amelioration of back pain during treatment.

REFERENCE: Behrend C, Prasarn M, Coyne E, et al. Smoking Cessation Related to Improved Patient-Reported Pain Scores Following Spinal Care. J Bone Joint Surg Am. 2012(Dec);94(23):2161-2166 [abstract here]

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