A Randomised, Patient-Assessor Blinded, Sham-Controlled Trial Of
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Johnson et al. Trials (2016) 17:574 DOI 10.1186/s13063-016-1709-2 STUDYPROTOCOL Open Access A randomised, patient-assessor blinded, sham-controlled trial of external non- invasive peripheral nerve stimulation for chronic neuropathic pain following peripheral nerve injury (EN-PENS trial): study protocol for a randomised controlled trial Selina Johnson1,2* , Roberta Richey1, Emily Holmes3, Dyfrig Hughes3 and Andreas Goebel1,2 Abstract Background: Eight percent of people in the UK are estimated to have persistent (chronic) neuropathic pain, and for many there is no effective treatment. Medications are the most common first-line treatment but often have limited benefit or adverse events. Surgical treatments, such as spinal cord stimulation, are then often considered. External non-invasive peripheral nerve stimulation (EN-PENS) is a form of electrical stimulation that involves placing a pen-shaped electrode onto the skin, which can be easily self-administered by patients. Observational studies suggest that EN-PENS may relieve pain for people with localised neuropathic pain; however, there is currently no evidence from controlled trials to confirm the efficacy and confidently determine the effect size for patients with longstanding neuropathic pain. Methods: EN-PENS is a single-site, blinded, randomised controlled parallel-group superiority add-on trial with a 1:1 allocation ratio, designed to evaluate the efficacy of treatment versus control treatment in 76 patients with longstanding neuropathic pain following peripheral nerve injury. Patients with moderate to -severe neuropathic pain following peripheral nerve injury will be randomised to receive either the active or control treatment, followed by an optional treatment extension or treatment switch to the alternative treatment arm. The primary outcome is average 24-h pain intensity recorded on an 11-point (0–10) numerical rating scale, averaged over the last 7 days of treatment. Discussion: Study results will be used to inform potential treatment efficacy and cost-effectiveness of EN-PENS for this population group. Trial registration: ISRCTN53432663. Registered on 7 July 2016. Keywords: Peripheral nerve injury, Neuropathic pain, External non-invasive peripheral nerve stimulation, Chronic pain * Correspondence: [email protected] 1The Walton Centre NHS Trust, Liverpool, UK 2The University of Liverpool, Liverpool L69 3BX, UK Full list of author information is available at the end of the article © The Author(s). 2016 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Johnson et al. Trials (2016) 17:574 Page 2 of 10 Background current density under the electrode [12, 13, 15, 18]. Pub- Neuropathic pain can arise peripherally or centrally as a lished evidence regarding the effects of LTD is largely direct consequence of a lesion or disease affecting the supported by animal and laboratory-based studies, but somatosensory system [1]. Pain can persist long after the as yet clinical human study evidence is lacking. initial cause has resolved. An estimated 8 in every 100 The first prospective cohort study on the use of EN- people in the UK have persistent chronic neuropathic PENS in neuropathic pain demonstrated significant pain pain [2, 3]. Neuropathic pain is often severely debilitating, reduction in persons with chronic neuropathic pain post it impinges on the physical, economic and emotional well- peripheral nerve injury (PPNI) or complex regional pain being of patients and is associated with low quality of life syndrome (CRPS) (n = 20, prospectively assessed, 2.8 (QOL) [4]. numerical rating scale (NRS) points average reduction, Neuropathic pain is very challenging to manage be- CI 1.6–4.0, p < 0.001). No treatment-related adverse cause of the heterogeneity of its aetiology and underlying events were reported. Significant improvements in QOL mechanisms [5]. (measured using the EuroQol (EQ)-5D-5 L) and function Current management guidelines are heavily weighted (using the Brief Pain Inventory Interference Subscale on pharmacotherapy, often with modest outcomes [6, 7]. and the task-specific scale) were also reported [19]. This When pharmacotherapy management is measured as study identified a trend toward patients with PPNI dem- sub-optimal, either due to adverse events or insufficient onstrating greater reductions in pain for longer periods pain relief, next-line therapy options include surgical than patients with CRPS. lesioning or neuromodulation therapy [8]. A disadvan- Further review of long-term EN-PENS efficacy (n =5, tage of surgical lesioning is that it is non-adjustable and average follow-up 3.5 years) indicated treatment benefits not reversible. Many procedures such as neurotomies have beyond those immediately following treatment [20]. The been discontinued in clinical practice. Neuromodulation analgaesic effect remained stable for at least 1 year, therapy involves using electrical or chemical technology with one to two treatments/day, with no evidence of that acts directly upon nerves to alter or modulate nerve tolerance. activity. The majority of neuromodulation technologies This initial study provides proof of concept for the are invasive. Treatments such as spinal cord stimulation efficacy of EN-PENS in reducing pain in persons with (SCS), dorsal root ganglion (DRG) stimulation and deep PPNI and CRPS who have moderate to severe pain brain stimulation (DBS) require surgical implants. Less in- intensity, with no adverse events reported. These data vasive technologies such as percutaneous electrical nerve suggest that this treatment may improve function and stimulation (PENS) involve electrical stimulation of nee- QOL. Therefore, the potential of EN-PENS as a safe, ef- dles inserted within the skin to target peripheral nerves fective and cost-effective treatment option for those with [9]. A disadvantage of such therapies is that the patient chronic neuropathic pain, for whom effective treatment will require invasive procedures to obtain benefits [10, 11]. options may be limited, warrants further consideration. Non-invasive neuromodulation technologies include Aside from the initial study described, current evidence external non-invasive peripheral nerve stimulation (EN- for this modality exists only in the form of conference PENS) and transcutaneous electrical nerve stimulation abstracts describing case series [21–25]. Results report (TENS). EN-PENS is a neuromodulation technology in positive responses in terms of immediate pain relief which an electrode is positioned on the skin over the following treatment primarily in patients with neuropathic injured nerve, and low-frequency electrical stimulation pain. (1–2 Hz) is applied to the nerve. This stimulation mode It is important to consider this potentially effective aims to achieve long-lasting analgaesia through a specific treatment in a randomised controlled trial (RCT) with a mechanism, preferential activation of superficial noci- larger group of patients. Previous study results do not ceptive A-delta fibres inducing long-term depression allow for the exclusion of possible moderate long-lasting (LTD) of synaptic strength [12–15]. These effects can changes in the pain intensity after stopping EN-PENS last up to a few days [16], rendering this an attractive treatment [19]; therefore, a crossover RCT design is not stimulation mode for intermittent applications. Patients feasible. can also easily be taught to self-administer treatment The primary objective of this trial is to establish clinical safely at home. efficacy and a more confident estimate of the effect size of In contrast to EN-PENS, TENS, another non-invasive EN-PENS treatment to reduce pain in patients with form of neuromodulation, typically activates A-beta moderate to severe neuropathic pain associated with fibres not involved in LTD when used in conventional definite or probable peripheral nerve injury. mode (50–100 Hz typically) [17]. Although when used at Secondary objectives are to evaluate the impact of this very low frequency it may theoretically elicit LTD, it treatment in terms of QOL and day-to-day function. then requires much higher current to overcome the low Further objectives are to gain a better understanding of Johnson et al. Trials (2016) 17:574 Page 3 of 10 this modality in respect to mood, self-efficacy (confidence arm will be offered (see the flow diagram of Fig. 1). The to perform abilities in the presence of pain), reduction of study duration will be 36 months (from study setup to allodynia, potential mode of action, cost-effectiveness and analysis). health care resource use (e.g. whether treatment can neg- ate the need for more complex surgical treatments and/or Setting reduce the need for drug treatment). This will be a single-site study conducted at a neurosci- ences research centre in a tertiary specialist neurosciences Methods hospital providing a pain management service. Trial design The EN-PENS trial is a single-site, blinded, randomised Recruitment and screening controlled parallel-group