Subcutaneous Peripheral Nerve Field Stimulation for Intractable Pain

Introduction

Spinal cord stimulation (SCS) has been accepted as a therapeutic modality for chronic complex pain conditions of the lumbar and cervical spine ( ). Although conventional SCS has been successful for the treatment of radicular pain, either upper extremity or lower extremity, it has been less effective for the relief of axial pain such as chronic low back pain (CLBP). The main reason for this lack of efficacy may be related to the difficulty for SCS to cover the painful lower lumbar area with epidural stimulation (paresthesia). This has led to the development of new approaches to more selectively stimulate areas of pain and provide more efficient paresthesia coverage, such as the introduction of peripheral nerve field stimulation (PNFS).

PNFS is described as electrical stimulation of a painful area by the percutaneous deployment of electrode(s) under the skin to electrically stimulate the end “arbors” of a peripheral nerve ( ). When electrodes are subcutaneously placed in the pain area, they stimulate the regional field of pain, including the local affected nerves and cutaneous afferents in the dermatomal distribution of the nerves, which then converge back into the spinal cord ( ). Successful use of PNFS has been reported for a variety of conditions, such as pain in the chest and abdominal wall, the pelvis or even shoulder girdle ( ), and axial CLBP and neck pain ( ) with good outcomes. Moreover, PNFS has been used as an add-on or combination therapy when SCS alone has not been sufficient in treating low back pain ( ). Recently, PNFS has become more popular and widespread because of its effective, reversible, and minimally invasive nature associated with low complication rates. It appears that the use of PNFS has opened new vistas for the management of a variety of painful conditions. In this chapter, we review procedural details of PNFS and results of the published studies to provide an overview and update on PNFS.

Patient Selection

Appropriate patient selection is a key factor for efficacy and good outcomes of PNFS. The inclusion criteria ( ) are the following:

• 1.

  A clearly defined, discrete focal area of pain with a neuropathic or combined somatic/neuropathic pain component

• 2.

  Failure to respond to medications, psychological therapies, physical therapy, pain management programs, and other surgical intervention, such as SCS

• 3.

  Psychological clearance

• 4.

  No coexisting chronic pain problems or neurologic diseases, and

• 5.

  No coexisting conditions that would increase procedural risks (e.g., sepsis, coagulopathy)

Surgical Implantation

Prior to the surgery itself, it is important to plan for the number of electrodes that will be required to successfully treat the pain in a person and in what position the electrodes should be placed to cover the painful area in its entirety ( ). Usually two to four electrodes are needed for most pain conditions, given that current implantable pulse generators (IPGs) offer multiple channels of stimulation. For this purpose, the anatomic atlas produced by Barolat is an excellent planning tool that can be used for proper choice of location and insertion approaches for subcutaneous electrodes ( ). Depending on the shape and size of the pain area, the electrodes could be placed in either a vertical, horizontal, or diagonal direction. For example, if the CLBP is located on only one side of the midline, one electrode is used and placed subcutaneously in the area of the worst back pain, in a direction perpendicular to the spinal axis. If the low back pain is on both sides of the midline, two electrodes can be placed, one on each side of the spinal column.

Efficacy of PNFS appears to be directly related to several key factors that include proper electrode placement and eliciting the appropriate sensation within the region of pain. The optimal depth of electrode placement is 10–12 mm beneath the skin surface ( ). More superficial placements of electrodes in the dermal layer may cause painful stimulation; on the other hand, implantation within deeper tissues may result in muscle recruitment and discomfort ( ).

The choice of the lead type is at the discretion of the physician. The goals of lead selection and placement are to cover the area of pain as completely as possible with paresthesia and to enable the greatest flexibility in subsequent programming. Either eight or four contact electrodes are used, in various combinations, to total 16, 24, or 32 programmable contacts, depending on the system/manufacturer used. Over time, as the overlap between maximum paresthesia coverage and maximum pain may vary or change, electrodes with more contacts provide greater programming options and versatility after surgery and therefore are selected in most cases ( ). The use of multicontact electrodes increases the options for programming parameters to stimulate precise areas of pain and may allow patients to independently modify the location and degree of stimulation in response to changes in activity or positioning, or fluctuations in pain severity ( ).