24 June 2010
Overview:
The use of electrical stimulation in the treatment of pain is not a new concept, as it in fact has origins in the time of the Roman Empire when the electric eel known as the torpedo fish was used to treat pain. In the more modern era, this application has evolved into the increasingly common use of Spinal Cord Stimulation for treatment of refractory pain conditions. Likewise, there have been increasing reports of utilization of stimulation peripherally in the form of Peripheral Nerve Stimulation (PNS) and Peripheral Nerve Field Stimulation (PNFS). Interestingly, Slavin has noted that, although implanted spinal cord stimulator devices have more “approved” indications, the first articles reporting implanted devices for Peripheral Nerve Stimulation predated those of spinal cord stimulation. [21]
First, it is helpful to discuss the similarities and differences between Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation. The former generally implies implantation of a stimulating electrode either directly on a particular nerve via surgical visualization (a summary of one group’s approach to this is detailed well in Mobbs et al, 2007) or perhaps more commonly percutaneous placement of a stimulating electrode in close proximity to a particular peripheral nerve. [15] In the latter, stimulating electrodes are percutaneously placed in the painful areas themselves without respect to a particular named nerve’s location. In both, the underlying concept remains the same: using electrical stimulation peripherally (as opposed to centrally in the case of dorsal column stimulation) to provide paresthesias in painful areas leading to pain relief. The exact mechanism(s) by which these approaches render pain relief is incompletely understood. A widely held hypothesis is that pain relief may be (at least in part) explained by the “gate-control” theory originally described by Melzack and Wall in their landmark paper published in 1965. The gate of pain transmission is opened by activation of nociceptive specific neurons, while stimulation of large myelinated fibers closes the gate. Putative inhibitory neurotransmitters thought to be released during large myelinated nerve fiber stimulation include gamma-aminobutyric acid (GABA) and adenosine. [11] [12] [9]
With regards to indications, it is generally accepted that Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation are modalities reserved for neuropathic pain that is refractory to conventional treatment methods. Neuropathic pain in this context would include a wide variety of pathologic conditions and the literature (as discussed later in this text) reports the use of Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation in conditions including chronic headache, post-herpetic neuralgia, abdominal pain, complex regional pain syndromes (CRPS) and post-thoracotomy pain among many others. The pain must be chronic and neuropathic in nature, with an intensity that negatively impacts the patient’s quality of life and/or ability to function. Most would likely agree that candidates for peripheral nerve/field stimulation should meet the same psychological criteria as those deemed suitable for spinal cord stimulation. Many implanters (and insurance carriers) actually insist upon formal psychology evaluation before deciding to proceed with trial and implantation of a peripheral stimulation device. Beyond these points, the actual selection criteria vary to a degree amongst practitioners, but converge on the fact that the painful condition must be consistently well localized. In some instances (such as supraorbital or greater occipital neuralgia), authors report using significant (albeit transient) response to peripheral blockade of the nerves in question as a screening criteria in order to consider trial of peripheral stimulation. [1] Others contend that response to nerve blocks are not predictive of success [19], and in some conditions (particularly those involving Peripheral Field Stimulation), a dedicated nerve-block may not even be an option as the painful area is not necessarily overlying a particular named nerve that is amenable to blockade. [21] The current literature no longer requires relief from peripheral blocks as a screening test for considering a trial of peripheral stimulation.
It should be noted that none of the most commonly implanted stimulator devices currently have FDA approval for use in Peripheral Nerve Stimulation and Peripheral Field Stimulation, and as such use in this context is “off label.”
Anatomy
As the conditions treated with Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation vary widely, the relevant anatomy for these procedures is a broad concept. As previously noted, this modality has been used for a myriad of conditions, and (considering the indications) could conceivably be applied almost anywhere on the body with chronic, neuropathic pain.
Procedure:
An advantage of using Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation as a modality for treating pain includes the fact the devices are nearly always trialed before a permanent implantation allowing for a “try before you buy” clinical situation. As the most frequently utilized method of lead placement at present is percutaneous, this will be the focus of this section. (As noted previously, Mobbs et al, 2007 contains an explanation of their surgical technique with a direct visualization method should further information on this technique be desired.)[15] Additionally, not unlike spinal cord stimulator placement, rarely is more than IV sedation or Monitored Anesthesia Care (MAC) needed, thus sparing the patient a general anesthetic in most cases.
The initial portion of the trial procedure and the permanent implantation are largely identical with regard to lead placement. In the case of Peripheral Nerve Stimulation, the appropriate anatomic location of the nerve to be stimulated is identified and prepped in a sterile fashion. Similarly in the case of Peripheral Nerve Field Stimulation, the area of the patient’s maximal pain is identified and marked preoperatively, then prepped in a sterile fashion. Following administration of appropriate sedation, local anesthesia is injected overlying the skin entry point. An introducer needle, such as a 14g Tuohy, is then placed subcutaneously to the target area (either the location of a particular nerve or the area of maximal pain). An electrode is then threaded into place through the Tuohy needle. Many practitioners will then obtain a fluoroscopic radiograph to verify and record lead placement. The Tuohy is subsequently removed and the lead is secured to the skin. Again not unlike the case in spinal cord stimulation, the lead is connected to an external pulse generator for the trial period. There is variability in the literature regarding the duration of the trial period as time frames of 2-14 days are commonly reported. There is general agreement that should there be >50% improvement in the patient’s symptoms, the trial is interpreted as positive, and the patient is scheduled for permanent implantation.
The permanent implantation procedure involves lead placement as previously described with suitable anchoring of the leads to an appropriate area (such as ligamentous tissue) and tunneling to a dissected pocket (in a preoperatively designated location chosen in concert with patient preference) where the leads are connected to an implanted pulse generator (IPG). Once verified to be connected appropriately and functional, the IPG is placed into the pocket, secured, and the incisions are closed. Both the trial and the permanent implantation procedures can be performed in the ambulatory setting, with no inpatient hospitalization required in most cases.
Benefits:
The lack of Class I and/or II evidence for Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation is mentioned frequently in discussions of this modality of therapy and editorials on the subject. Though a randomized controlled trial would certainly be a welcomed piece of supporting evidence for this therapy, it may not be practical to pursue. Mobbs et al, point out that “a study that included randomizing patients to a ‘best medical therapy’ versus a peripheral nerve stimulator would be ideal, although not feasible as these patients are referred because they have failed the ‘best medical therapy‘ option.” [15]
Although there is lack of large randomized controlled trials studying PNS and PNFS, the available data overall suggest that this is a safe and effective modality for the treatment of otherwise refractory pain of a variety of etiologies. In their recent review of the available evidence published on the subject of peripheral neuromodulation, Bittar and Teddy state: “The published studies suggest that a significant proportion (60-70%) of patients with certain intractable pain syndromes will benefit from peripheral nerve stimulation...the risk of serious adverse events is relatively low.” [3]
With regards to intractable headache, there have been several studies that looked at the use of Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation in addressing various types of headache. Overall, this data has been positive. For instance, in transformed migraine and occipital neuralgia, a number of studies of occipital nerve stimulation (as summarized by Bittar and Teddy) have shown decreased frequency and/or intensity of headache symptoms with occipital stimulation. [3] [19] [17] [22] Additionally there is promising data on use of supraorbital stimulation. [1]
Post Herpetic Neuralgia can be an extremely painful condition refractory to medications and many percutaneous interventions. Case reports addressing the use of Peripheral Nerve Field Stimulation for PHN have been encouraging; though represent a limited number of patients. [7][10][18][23]
Abdominal Pain can present a challenge to the Pain Medicine Physician on account of multiple etiologies and limited diagnostic studies for determining the source of pain. A 2006 case report by Paicius et al reports the use of Peripheral Nerve Field Stimulation in three patients with refractory abdominal pain of different etiologies, all of which derived “significant relief from pain, enabling patients to decrease or discontinue their opioid medications and to enjoy significant improvement in their quality of life.” [16] This series suggests that abdominal wall pain that is neuropathic may respond well to peripheral neuromodulatory techniques.
With respect to Complex Regional Pain Syndrome (formerly called Reflex Sympathetic Dystrophy), Hassenbusch et al published a study in 1996 documenting long-term results of PNS in a subset of CRPS patients. In their work >60% of patients experienced fair to good relief of symptoms as far out as 4 years, which was consistent with the 60% rate of >50% pain reduction reported by Mobbs et al in patients with isolated nerve injuries and neuropathic pain. [8][15]
Risks:
The overall risk of serious complications with Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation appears to be very low. Peripheral neuromodulatory techniques avoid the spinal canal, and as a consequence, the risk of bleeding and/or infection into the epidural space resulting in possibly catastrophic neurologic deficit or need for emergent spine surgery are essentially nil. Bleeding and infection associated with the implantation are still a possibility with the infection rate estimated to be between 3-5% [6]. Other possible complications include hardware complications such as skin erosion of components, lead migration, component breakage or disconnection, and superficial foreign body reaction to components. Additionally, persistent hardware pain can occur (estimated at a rate of 5%) [6], and can be significant enough as to result in explantation of the device (author’s experience).
Contraindications differ between implanters for Peripheral Nerve Stimulation and Peripheral Nerve Field Stimulation but include active infection, anticoagulation or coagulopathy, and untreated psychological conditions. Whether or not to include unresolved litigation concerning the underlying pain condition as a relative contraindication remains a controversial topic.
References:
- Amin S et al. Peripheral nerve stimulator for the treatment of supraorbital neuralgia: a retrospective case series. Cephalalgia 2008; 28:355-9.
- Bhatnagar S et al. Peripheral nerve field stimulation for intractable post-thoracotomy scar pain not relieved by conventional treatment. Pain Practice 2010.
- Bittar RG and Teddy PJ. Peripheral neuromodulation for pain. Journal of Clinical Neuroscience 2009; 16:1259-61.
- Broggi G et al. Neuromodulation for refractory headaches. Journal of the Neurological Sciences 2010; 31(supp 1): S87-92.
- Coffey RJ and Lozano AM. Neurostimulation for chronic noncancer pain: an evaluation of the clinical evidence and recommendations for future trial designs. Journal of Neurosurgery 2006; 105:175-89.
- De Leon-Casasola, OA. Spinal cord and peripheral nerve stimulation techniques for neuropathic pain. Journal of Pain and Symptom Management 2009; 38(supp 2): S28-38.
- Dunteman E. Peripheral nerve stimulation for unremitting ophthalmic postherpetic neuralgia. Neuromodulation. 2002; 5:32-7
- Hassenbusch SJ et al. Long-term results of peripheral nerve stimulation for reflex sympathetic dystrophy. Journal of Neurosurgery 1996; 84:415-23.
- Linderoth B et al. Dorsal column stimulation induces release of serotonin and substance P in the cat dorsal horn. Neurosurgery 1992; 31:289-97
- Kouroukli I et al. Peripheral Subcutaneous Stimulation for the treatment of Intractable Postherpetic Neuralgia: Two case reports and literature review. Pain Practice 2009; 9:225-229.
- Melzack R and Wall PD. Pain mechanisms: a new theory. Science 1965; 150: 971–979
- Meyerson BA; Linderoth B. Mode of action of spinal cord stimulation in neuropathic pain. Journal of Pain and Symptom Management 2006; 31(4 Suppl): S6-12.
- Meyerson et al. Spinal cord stimulation in animal models of mononeuropathy: Effects on the withdrawal response and the flexor reflex. Pain 1999; 79:229-43
- Mirone G, Natale M and Rotondo M. Peripheral median nerve stimulation for the treatment of iatrogenic complex regional pain syndrome (CRPS) type II after carpal tunnel surgery. Journal of Clinical Neuroscience 2009; 16:825-7.
- Mobbs RJ, Nair S and Blum P. Peripheral nerve stimulation for the treatment of chronic pain. Journal of Clinical Neuroscience 2007; 14:216-21.
- Paicius R, Bernstein CA and Lempert-Cohen C. Peripheral Nerve Field Stimulation in Chronic Abdominal Pain. Pain Physician 2006; 9:261-6.
- Popeney CA, Alo KM. Peripheral neurostimulation for the treatment of chronic disabling transformed migraine. Headache 2003; 43:369-75
- Rodrigo-Royo MD, Azcona JM, Quero J, Lorente MC, Acin P, Azcona J. Peripheral neurostimulation in the management of cervicogenic headache: four case reports. Neuromodulation. 2005; 8:241–248
- Schwedt et al. Occipital nerve stimulation for chronic headache- long term safety and efficacy. Cephalalgia 2007; 27:153-7
- Schwedt TJ et al. Response to occipital nerve block is not useful in predicting efficacy of occipital nerve stimulation. Cephalalgia 2007; 27:271-4
- Slavin KV. Peripheral Nerve Stimulation for Neuropathic Pain. Neurotherapeutics 2008; 5:100-106.
- Trentman TL et al. Greater occipital nerve stimulation via the Bion microstimulator: implantation technique and stimulation parameters. Pain Physician 2009; 12:621-8.
- Yakovlev AE, Peterson AT. Peripheral nerve stimulation in treatment of intractable postherpetic neuralgia. Neuromodulation 2007; 10:373–375
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