Периферическая нейростимуляция в лечении постламинэктомического синдрома

Хроническая боль в спине у пациентов с постламинэктомическим синдромом плохо поддается консервативной терапии и общепринятым минимально инвазивным методам лечения, в том числе спинальной доставкой лекарственных препаратов и центральной нейростимуляцией. Наш опыт включает 98 пациентов с хронической болью в спине и нижних конечностях, возникшей вследствие постламинэктомического синдрома, которым была проведена имплантация систем для периферической нейростимуляции. Стимуляция осуществлялась путем подкожной имплантации двух 8-контактных электродов в поясничной области. У большинства пациентов мы наблюдали отчетливый противоболевой эффект в течение 2-дневной тестовой стимуляции. Через 2-4 нед проводилась имплантация постоянных систем для периферической нейростимуляции с использованием подзаряжающихся и неподзаряжающихся генераторов. Через 12 мес 84 пациента (85,7%) отмечали выраженный противоболевой эффект (более 75% уменьшение интенсивности боли по VAS-шкале). Таким образом, по нашим данным, периферическая нейростимуляция является эффективным методом лечения пациентов с постламинэктомическим синдромом, у которых продолжается некурабельная боль в спине, несмотря на консервативную терапию. Периферическая нейростимуляция обеспечивает более эффективный контроль боли в сравнении с консервативным лечением, спинальной стимуляцией и целевой доставкой лекарственных препаратов. Периферическая стимуляция может быть рекомендована как приоритетная методика для обсуждаемой нозологической группы.

Postlaminectomy syndrome (PLS) occurs in patients who underwent spinal operations for such conditions as spinal instability, disc herniation, or spinal stenosis. There are multiple causes of PLS including spinal instability, disc herniation or epidural fibrosis and arachnoiditis [1-2]. The management of chronic low back and lower extremity pain associated with postlaminectomy syndrome can be difficult in clinical practice. Spinal cord stimulation (SCS) has been effective to control radicular pain, but not as consistently beneficial in management of axial low back pain [3-10]. Recent advances in SCS technology allows for better control of low back pain [11] but it remains a challenge in the treatment of patient with PLS. After implantation of SCS, patients may continue to experience significant low back pain, requiring frequent interventional pain procedure including epidural and facet blocks, trigger point and sacroiliac joint injections, and continued use of different pain medications and oral opioids. Some of these patients undergo implantation of intrathecal pumps.

Many interventional pain specialists describe difficulty achieving adequate coverage of pain in the lumbosacral area during the SCS trial or maintaining adequate axial low back pain control over the long term after implantation of SCS for patients with PLS. During the SCS trial the patients may experience uncomfortably strong stimulation in the legs, flanks, abdomen or even chest wall while attempting to obtain adequate stimulation in low back [3, 12]. This problem can contribute to the trial failure. At present time there is no clear understanding regarding the mechanism by which, in the absence of lead migrations, changes in the patterns of stimulation SCS over time becomes ineffective for control of low back pain [13].

Peripheral nerve field stimulation (PNFS) has been used to treat a variety of neuropathies [14], including ileoinguinal [15], occipital [16-19], post-herpetic [20], intercostals [21], for treatment of trigeminal postherpetic neuralgia and trigeminal posttraumatic neuropathic pain [22-25] with excellent relief of pain and reduced need for oral pain medications. Recent reports describing treatment of low back pain by using stimulation through the leads placed subcutaneously in areas with localized pain [3, 6, 13, 26, 27] demonstrated good efficacy, simplicity and low morbidity of this novel technique.

Methods

Between September 2005 and May 2012, 98 patients with chronic low back and lower extremity pain associated with postlaminectomy syndrome underwent PNFS placement. Sixty one of them were males and thirty seven were females. Patient gender distribution was 62.2% male, 37.8% female with mean age 57 years, ranging from 32 to 90 years. Most patients, 89.8%, had over 12 months of previous pain duration. In this group, 36 (37%) patient already had implanted SCS and eleven (11%) patients had preexisting intrathecal pumps but continued suffering from intractable low back pain. No patients were involved in active litigation. All patients failed conservative therapy and had short lasting pain relief after different injections.

Following psychological evaluation and clearance for advanced interventional pain procedures, patients underwent successful trial of percutaneous placement of two 8-electrode standard Octad Leads subcutaneously (Medtronic Inc., Minneapolis, MN). After local infiltration of 1% lidocaine, the leads were inserted through 14 gauge Touhy needles (Fig. 1). The leads were placed vertically, parallel and lateral to postoperative scar in the area of maximum pain (Fig. 2). Both leads were connected to temporary extension cable and to a temporary external stimulator. During the 2 day PNFS trial the patients reported greater than 50% improvement in pain. Stimulator parameters programmed for amplitude between 1.8 and 3.2 volts, pulse width 350 to 450 microseconds, and frequency 40-50 Hz. Two to four weeks later the patients underwent implantation with permanent leads through small perpendicular to midline incisions made in the paraspinal areas of the lumbar region (Fig. 3). The leads were passed through slightly bent 14 Gauge Tuohy needles to follow the curvature in lumbar area. Positioning of the leads was done with C-arm guidance (Fig. 4) to assure proper placement and to avoid potential damage of existing electrodes in the group of patient with previously implanted SCS or prevent laceration of intrathecal catheter for the patients with IT pumps. Both leads were anchored in the wound to fibroaponeurotic tissue with 2-0 nonabsorbable suture of braided polyester (Ethibond) and Titan Anchors (Medtronic Inc., Minneapolis, MN). The leads were tunneled to the left or right supragluteal areas where the subcutaneous pocket was created for the generator. Leads were then connected to a rechargeable Restore (Medtronic Inc., Minneapolis, MN) or non-rechargeable generators Restore Ultra (Medtronic Inc., Minneapolis, MN). All procedures for permanent implantation were performed with conscious sedation and local anesthesia. The post- operative course was uneventful. The stimulator was programmed using a guarded electrode configuration with a pulse width of 450 microseconds and a rate of 60 Hz. The amplitude use ranged from 1.5 to 2.3 volts.

Electrode polarities were set as follow:

PNFS alleviates pain by subcutaneous stimulation of the peripheral fibers, which may prevent transmission of painful impulses to the central nervous system. The neuromodulating effects of electrical stimulation are based on the tenets of the "gate-control theory" of pain proposed by Melzack and Wall in 1965 [28]. Based on this theory, it is hypothesized that PNFS "closes the gate" to pain transmission by activating large-diameter afferent fibers via application of an electric field. PNFS may also alter local blood flow, cause release of endorphins, affect neurotransmitters and axonal conduction, and may block cell membrane depolarization [14]. The mechanism of action of PNFS and neuromodulation in general continues to be investigated as there may be a multitude of ways in which neuromodulation effects pain transmission. PNFS works on the painful areas of the low back which is sometimes very difficult to target with epidural stimulation. In our experience, the patients had better coverage of the pain areas with vertical positioning of the leads because greater involvement of the endings posterior primary division of lumbar spinal nerves which emerging almost perpendicular to subcutaneously placed leads. We believe this technique of lead placement allows for the stimulation of more dermatomal nerves, capturing the broadest possible zone corresponding to the area of low back pain and positively influencing outcomes of trials and final implant procedures.

Presented in this report is the data on patients with PLS implants that suffered from intractable, refractory-to-conventional-treatment low back pain and were successfully treated with PFNS. This technique may be a safe and effective treatment for patients who have not found relief with conservative measures or who are not appropriate candidates for more invasive interventional pain or surgical procedures based on their co-morbid health conditions. This technique is easier to perform in comparison to SCS and it avoids potential complications related to epidural lead placement. PNFS can be considered as preferable option for patients with more prominent low back then leg pain before offering a patient SCS trial. PNFS has provided these patients with satisfactory pain relief without the side effects of previous medication therapy. PNFS offers a safe and effective treatment method that is completely reversible should a patient lose its pain-alleviating effect. In addition, there is no unpleasant weaning process required if a patient desires or needs to discontinue therapy for any reason. This study provides support for PNFS as an alternative treatment option for patients with intractable low back pain and will hopefully inspire interest in prospective studies comparing peripheral nerve stimulation to other therapies.

Our study represents retrospective data, it may be possible in the future to design study comparing two groups of patients with vertical and horizontal positioning of the leads. Future studies should include more detailed outcome measurements like Oswestry scales before and after stimulation. A smaller observational study may be indicated to observe more in-depth improvements in activities of daily living and decrease in medication including opioid use.