To the Editor:
A recent article in Anesthesiology by Schukro et al.1 concluded that duloxetine is superior to placebo for the treatment of chronic low back pain (LBP) associated with neuropathic pain in the lower limb. I commend the authors for their efforts in adding to the literature on therapies for this subgroup of patients with LBP. However, I have a few questions regarding the methodology of this article and some suggestions that may be useful for future investigations on this topic.
First, the title of the publication is confusing because it gives the impression that trial participants had pain with a neuropathic component in their lower back. Several recent publications (including some referenced by the authors) have focused on this aspect of LBP.2–4 However, the focus of treatment in the trial by Schukro et al. was radicular pain in the lower limb. Second, the diagnosis of radiculopathy secondary to intervertebral disc herniation or spinal canal/foraminal stenosis should have been confirmed through documentation of neurologic deficits on physical examination or the use of magnetic resonance imaging or electrodiagnostic studies. I respectfully submit that diagnosing radicular pain on the basis of the distribution and characteristics of pain is suboptimal, especially in the context of a clinical trial. Two references5,6 quoted by the authors in support of this approach are more than 40 yr old, and some of the other more recent publications7,8 referenced by Schukro et al. are investigations that focused on identifying neuropathic back (and not leg) pain.
Third, pain scores should have been measured distinctly for LBP and radicular pain in the lower limb. A recent study by Cohen et al.9 that compared the efficacy of gabapentin and epidural steroid injections in patients with lumbosacral radicular pain demonstrates the importance of rigorous inclusion criteria supported by diagnostic modalities and serial measurement of pain in different locations. Another potential option is to consider patients with only neuropathic LBP.10
In addition, the authors could have considered the use of a measurement tool to evaluate the neuropathic component of the pain over time (pre and post treatment). The Neuropathic Pain Symptom Inventory is an example of such a tool that has the ability to detect the effects of treatments for neuropathic pain over time.11 The authors used painDETECT serially (at baseline and at 4 weeks after the intervention), but this is a screening tool for neuropathic pain and, as acknowledged by the authors, it may not have the sensitivity to reflect the change in the neuropathic component of pain over time. Last, although the authors have provided some information about calculation (and recalculation) of the sample size, the final number of participants (25) seems unusually low. Can the authors kindly provide SDs that were used for the first and second calculations of sample sizes?
The author declares no competing interests.