This Invited Commentary accompanies the following original article:
Beloeil H, Sion B, Rousseau C, et al. Early postoperative neuropathic pain assessed by the DN4 score predicts an increased risk of persistent postsurgical neuropathic pain. Eur J Anaesthesiol 2017; 34:652–657.
More than 300 million surgical procedures are performed worldwide every year and a substantial proportion of patients still report severe pain during the first 24–48 h, even after minor procedures.1 Moreover, 11.8% [95% confidence interval (CI): 9.7 to 13.9%] will suffer from chronic post-surgical pain (CPSP), defined as pain that persists longer than the normal healing period of 3 months.2 CPSP can be severe in 2.2% of patients and, depending on the type of surgery, is often neuropathic. In patients with severe CPSP, some 30% (range, 6 to >54%) have signs of neuropathic pain.3,4 When neuropathic pain is present, pain intensity and its impact on quality of life are generally higher.2,4
For International Association for the Study of Pain, 2017 is the ‘Global Year against Pain after Surgery’. In the light of the aforementioned problems regarding the control of both acute and chronic pain after surgery, and keeping in mind that poorly relieved postoperative pain is a major risk factor for the development of persistent pain after surgery,4,5 the presence of a neuropathic component in acute pain and its relationship with severe persistent post-surgical pain certainly deserves attention.
In this issue of the journal, Belloil et al.6 from the Societé Française d’Anesthésie-Réanimation Research Network have assessed the presence of a neuropathic component in acute postoperative pain within the first 48 h after surgery and again at 2 months. In a cohort of 593 patients, using the DN4 (Douleur Neuropathique 4) questionnaire,7 the authors found neuropathic pain to be present in 5.6 and 12.9% of patients suffering from acute postoperative pain on days 0 and 2, respectively. At 2 months, 39% of patients still had pain and a neuropathic component was present in 33% of these.
These results deserve comment, as studies on the prevalence of neuropathic pain immediately after surgery are extremely scarce. However, care is required when interpreting this 13% prevalence of acute neuropathic pain as reported by the authors as this determination was based on the DN4 alone, a screening tool that has not been validated in this setting. Of note, a prospective study of all patients referred to an Australian acute pain service identified patients with neuropathic pain using clinical history and examination only: they found an overall incidence of 1.04%.8 The diagnosis of neuropathic pain in patients with acute postoperative pain is challenging, as many of the characteristics considered by pain experts as useful for the diagnosis of acute postoperative neuropathic pain (e.g. burning pain, allodynia and hyperalgesia) can also be encountered in postoperative inflammatory pain, or as a consequence of primary and secondary hyperalgesia.9 Moreover, the criteria used to diagnose neuropathic pain10 are not always applicable in the immediate postoperative setting. In addition, neurological examination is difficult in patients with limited mobility or with dressings that interfere with sensory assessment, and confirmatory tests are rarely available or contributive early after nerve injury. Similarly, the DN4 has not been specifically validated for neuropathic pain screening 2 months after surgery. Nevertheless, the DN4 has been used in large epidemiological studies,3,4 and some small studies show similar sensitivity and specificity for the detection of clinically diagnosed neuropathic pain in both subacute11 and chronic postoperative pain patients.12,13
The second objective of Beloeil et al.6 was to confirm, in a general population, the association between acute neuropathic pain after surgery and persistent post-surgical neuropathic pain (PPSNP) at 2 months, as has been previously reported for chronic post-surgical neuropathic pain after thoracic14 and iliac crest surgery15 after 3 months. The authors found that acute postoperative neuropathic pain identified on day 2 was associated with severe persistent post-surgical pain still involving a neuropathic component 2 months after surgery. These findings support the fact that early neuropathic pain as identified by a DN4 questionnaire may be a risk factor for PPSNP (OR 4.22; 95% CI 2.19 to 8.12).
These results raise the question of the use of screening questionnaires in the acute postoperative phase in the hope of improving patient outcomes. If at-risk patients can be identified early in the postoperative period, one could speculate, as do the authors, that tailored treatment at this stage could prevent the development of chronic pain. Such interventions will probably necessitate a longer follow-up period than the 2 months in the present study, especially as CPSP is not a static phenomenon but rather fluctuates with time. Pain can resolve or appear, even several years after surgery.16 It is also well known that there can be a pain-free interval between a nerve injury and the onset of neuropathic pain.17 Moreover, pain characteristics can vary over time. A large prospective study recently found that the neuropathic character (evaluated with the DN4) of persistent pain after various types of surgery changes between 3 and 6 months in 25% of patients.3 Similar findings have been reported up to 3 years after knee surgery.18
So, what is the way forward? From a research agenda point of view, to understand the dynamic nature of CPSP better, we need longitudinal studies with a long follow-up and assessments at multiple time points. Ideally, in addition to screening questionnaires, these studies should incorporate standardised sensory testing to assess pain characteristics more reliably. The role of neuropathic pain screening questionnaires and their performance in this setting should also be clarified. Finally, we should set up randomised studies to test tailored, multidisciplinary interventions aimed at at-risk patients, for example those displaying neuropathic pain symptoms in the acute postoperative phase. From a clinical point of view, this study adds a positive DN4 score in the immediate postoperative period to the already known risk factors for CPSP5 and underscores the need to set up pain management programmes dedicated to the follow-up of surgical patients, not just in the acute postoperative period but also after their discharge from the hospital.19
Acknowledgements relating to this article
Assistance with the commentary: none.
Financial support and sponsorship: none.
Conflicts of interest: none.
Comment from the Editor: this Invited Commentary was checked by the editors but was not sent for external peer review. PL is an Associate Editor of the European Journal of Anaesthesiology.
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