Comment on Abdel Shaheed et al.: “Efficacy and tolerability of muscle relaxants for low back pain: Systematic review and meta‐analysis”

To the Editor: I read with interest the systematic review by Abdel Shaheed and colleagues published on June 22, 2016 (Abdel Shaheed et al., 2016). In their systematic review and meta-analysis on the efficacy and tolerability of muscle relaxants for low back pain (LBP), the authors reported that muscle relaxants provide clinically significant pain relief in patients with acute LBP. Similar observation was reported in a systematic literature review on eperisone (a centrally acting muscle relaxant) in acute LBP patients (Bavage et al., 2016). I have few queries on the methodology and main conclusion of the systematic review, and I request the authors to address the same. First, the systematic review included published randomized controlled trials (RCTs); the authors could have also searched for grey RCTs which meet the inclusion criteria of this systematic review (NCT00671879 and NCT00671502, Table 1). Furthermore, the authors could have also requested sponsors/original investigators for data of the completed trials without results in the US National Institutes of Health database (NCT02646124, NCT00679146, NCT01300312, and NCT01806818, Table 1) (Young and Hopewell, 2011). Including unpublished trials in the meta-analysis are useful to assess the presence and magnitude of publication bias (McAuley et al., 2000; Conn et al., 2003; Hopewell et al., 2007; Furlan et al., 2015). The authors, however, reported this as one of the major limitations of their systematic review which possibly included potential publication bias. Second, under study selection the authors stated that only placebo-controlled RCTs and RCTs comparing two drugs from the same class or different doses of the same drug were eligible for inclusion. Furthermore, they reported that no eligible RCTs evaluating benzodiazepines in LBP were identified. However, there is a RCT conducted by Rusinyol and colleagues which meets the inclusion criteria (Rusinyol et al., 2009). This trial evaluated the efficacy and tolerability of two different doses of eperisone (150 and 300 mg/day) vs. diazepam (15 mg/day) in acute LBP patients and also performed intergroup comparison between two different doses of eperisone. Exclusion of this RCT might have also contributed to publication bias. Third, the metaanalysis was performed on pain and disability outcomes (primary endpoints) converted to a common 0–100 scale (Figures 2 and 4; Table S7) and adverse event rates for muscle relaxant vs. placebo trials (Table S5) (Abdel Shaheed et al., 2016). In addition, the authors could have also meta-analysed global measure (overall improvement, percentage of patients reporting subjective improvement) and physiological outcomes (e.g. hand-to-floor distance, Lasegue test) which also play important role in assessing the efficacy of muscle relaxants for LBP (van Tulder et al., 2003; Furlan et al., 2015; Gagnier et al., 2016). Last, in the abstract, what does this review add? and discussion, the authors reported that muscle relaxants provide clinically significant short-term pain relief for people with acute LBP. However, under Conclusion the authors quoted that “muscle relaxant drugs do not provide clinically significant pain relief in the short term for people with acute LBP. ” I am eager to know the authors’ view on this.