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Neuropathic pain: mechanisms and their clinical implications

BMJ 2014; 348 doi: https://doi.org/10.1136/bmj.f7656 (Published 05 February 2014) Cite this as: BMJ 2014;348:f7656

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Re: Neuropathic pain: mechanisms and their clinical implications

We would like to thank Dr. Andrew for his insightful letter, and for pointing out the error in our article (1). Whereas the definition of neuropathic pain in our glossary of terms was updated, the definition contained in the text of the article used the older definition. The reason this error arose is because although we used the IASP website (2) as a resource for determining what terms to define and how best to define them, for definitions contained within the article itself, we tried to reference articles published in journals. The Treede et al. (3) article cited provided a rationale for replacing the older definition with the newer one, and we mistakenly used the older one. This error was not detected until after publication.

Two points Dr. Andrew’s comments highlight are the evolving nature of what constitutes neuropathic pain, and the inherent subjectivity in its diagnosis. This ambiguity is accentuated for functional disorders such as complex regional pain syndrome and fibromyalgia in which the degree of pain is disproportionate to physical findings. For example, a recent study found the painDETECT instrument to be inaccurate in patients with fibromyalgia and a concomitant, clinically-confirmed neuropathic pain condition (4). However, given the overlap in mechanisms between neuropathic and non-neuropathic pain, and the lack of specificity for analgesic medications, the clinical implications of changes in our definition of neuropathic pain may be overestimated.

References
1. Cohen S, Mao J Neuropathic pain: mechanisms and their clinical implications BMJ 2014; 348: f7656
2. International Association for the Study Pain. IASP Taxonomy. Available at: http://www.iasp-pain.org/Education/Content.aspx?ItemNumber=1698. Last updated May 22, 2012, last accessed March 15, 2014.
3. Treede RD, Jensen TS, Campbell JN, Cruccu G, Dostrovsky JO, Griffin JW, et al. Neuropathic pain: Redefinition and a grading system for clinical and research purposes. Neurology2008; 70: 1630-5.
4. Gauffin J, Hankama T, Kautiainen H, Hannonen P, Haanpää M. Neuropathic pain and use of PainDETECT in patients with fibromyalgia: a cohort study. BMC Neurol 2013; 13:21.

We appreciate the comments from Manchikanti et al, and have acknowledged the source of our error in the text in our response to Andrew. In our glossary, we used the updated definition. In reviewing the authors’ response, we would like to point out an error they made in the study by Freynhagen and colleagues (1). In an attempt to illustrate the problems with a liberal definition of neuropathic pain, they mistakenly wrote that the authors found that 37% of patients with non-radicular back pain were determined to have predominantly neuropathic pain. In fact, in the larger epidemiological study they performed, the authors did not note the specific type of back pain, stating only that they included “…7772 patients with various forms of chronic low back pain…”. This estimate actually falls somewhere in the middle of the cited prevalence estimates of neuropathic pain in chronic low back patients, which range from 17% to 55%, with a median of 41% (2). Clearly, the controversy surrounding what constitutes neuropathic pain is a consequence of our lack of understanding regarding the mechanisms, the overlap in the putative mechanisms and treatments for neuropathic and non-neuropathic pain, and the inherent subjectivity in the pain experience.

References

1. Freynhagen R, Baron R, Gockel U, Tölle TR. painDETECT: a new screening questionnaire to identify neuropathic components in patients with back pain. Curr Med Res Opin 2006; 22: 1911-20.
2. Cohen SP, Jamison D, Bicket M, Wilkinson I, Rathmell JN. Epidural steroids: A comprehensive, evidence-based review. Reg Anesth Pain Med 2013; 38: 175-200.

Competing interests: No competing interests

16 March 2014
Steven P Cohen
Physician
Jianren Mao
Johns Hopkins
550 North Broadway, Suite 301