Effects of smoking on pain intensity in patients with chronic pain: are there clinical implications?

Ann Palliat Med 2020 | http://dx.doi. org/10.21037/apm.2020. 01.02 The association between smoking and the presence of chronic pain is well established, and consistently found in studies that span various times and geographic locations (1-7). Less reported is the association between smoking and pain intensity (8). The recent publication by Khan et al. (9) provides a statistical analysis of a large sample of patients seen at a tertiary chronic pain center, providing further insight on the relationship between smoking and pain intensity. The authors are to be commended on leveraging such a large amount of data from an institutional registry over a period of nearly 5 years. Using robust statistical analysis, the authors concluded that “patients with chronic pain who smoke have worse pain, functional, sleep, and psychological and mood outcomes compared with nonsmokers. Smoking also has prognostic importance for poor recovery and improvement over time”. The overall health benefits of not smoking as well as a smoke-free environment are universally accepted (10,11). Any information that furthers our understanding of the adverse effects of smoking is helpful from a public health perspective. Such information may also lead to better treatment of smoking and its associated health problems. With that in mind, there is value in putting the findings of Khan et al. into clinical context (9). Khan et al. note that the prevalence of smokers within their patient cohort to be 9.25%, similar to the cited smoking prevalence in California of the general population of approximately 10% (9). Smoking and pain is most established in research through population studies demonstrating that the presence of smoking increases the risk of an individual experiencing pain (1-7). Based on this, it is interesting that the incidence of smoking within their cohort of chronic pain patients was not higher than that of the general population. Other findings within demographics of this cohort were the relatively low prevalence of “history or depression” and “history of anxiety”, both of which have been associated with the presence of chronic pain (12-15). Higher levels of education that may be typically expected in a chronic pain patient population were also seen in this study. This most certainly reflects the referral patterns of the clinical as well as regional demographics. However, these differences in their patient population may limit the external validity of the data to other regions or chronic pain clinic patient populations. Quantitatively, the results must also be put into clinical context. The mean in “pain intensity now” at time 1 was 6.09 in smokers and 4.89 in non-smokers, with a mean difference of 1.2. While concepts of minimally clinically important difference (MCID) and minimal detectable change (MDC) are best suited to look at within group changes, the concept still applies in the analysis of this data. A cited value for MCID on the NRS scale is 2 (16) and similarly, greater than 1.5 is most commonly cited as the MDC (17-19). The interpretation of this is that for a Editorial Commentary