Abstract
Chronic pain in the cervical region that radiates to the shoulders and upper extremities is a common clinical problem. Van Zundert and colleagues’ article reports a randomized, double-blind trial of pulsed radiofrequency in chronic radicular neck pain patients (23 screened from 256) resulting in a statistically significant short-term efficacy measured as better global perceived effect and a 20-point reduction in a visual Analogue Scale. The trial reports no complications and displays significant reduction in analgesic use 6 months post procedure. This is the third published study highlighting the innovative application of radiofrequency (first to use pulsed radiofrequency) to treat this difficult pain syndrome.
The treatment of chronic cervical radicular pain (chronic neck pain with radiation to the shoulders and upper extremities) is limited to neuropathic analgesic agents, epidural steroid injections and cervical fusion surgery. Evidence for efficacy of these modalities is scant. In view of much needed novel therapies for this pain syndrome, Van Zundert and colleagues report a randomized, controlled trial Citation[1] that follows a clinical case series of successful pain relief with pulsed radiofrequency (PRF) of the cervical dorsal root ganglion (DRG) Citation[2]. Earlier studies carried out by van Kleef and colleagues Citation[3] and Slappendel and colleagues Citation[4] employed conventional radiofrequency (RF) techniques adjacent to the cervical DRG with some success.
The efficacy observed with PRF is debatable, but is purported to be due to neuromodulatory mechanisms suggestive of unique electric field-induced neuronal changes and selective long-term depression of small-diameter fibers, such as C-fibers, which are unrelated to thermal coagulation (the hallmark of conventional RF).
Methods & results
After Institutional Review Board approval, the authors screened 256 patients who were referred to a tertiary pain center over a period of 2.5 years. However, they could enroll and randomly allocate only 23 patients (PRF = 11 and sham = 12).
Patients with previous cervical laminectomy or fusion were excluded. Patients were between the ages of 20 and 75 years, reported cervical radicular pain for the previous 6 months that was not responsive to medications, physical therapy or transcutaneous electric nerve stimulation, had a positive Spurling’s test, and demonstrated signs of radicular component to neck pain confirmed with diagnostic blocks of suspected DRGs with 2% lidocaine. The DRG at the level with greatest analgesia following diagnostic blocks was chosen for subsequent PRF. In a double-blinded fashion and after positive response to sensory stimulation, PRF was administered at the involved DRG for 120 s.
Global perceived effect (7 point Likert scale), visual analogue scale (0–100), analgesic use (WHO scoring) and quality of life (Short Form Health Survey [SF-36] and Euroqol) were evaluated at 1, 3 and 6 months.
At 3 months, the outcomes, 50% or more reduction in global ‘perceived effect’ (p = 0.03) and 20-point reduction in VAS score (p = 0.02), showed statistical significance in the PRF group compared with the sham group. The other two primary outcomes, ‘reduction in analgesic use’ and ‘quality of life’ were not statistically significantly different between the two groups at 3 months. At 6 months, the only outcome that showed statistical significance was ‘reduction in analgesic use’.
Discussion
Although the idea of PRF of DRG for cervical radicular pain was first tested in a randomized, controlled trial, in this study several issues limit the applicability of its results. Due to significant differences in baseline demographics and lack of adequate sample size, the results may not be robust. It is unclear whether any of the enrolled patients had received epidural steroid injections prior to study participation.
Expert commentary
Radicular neck pain is an etiologically complex clinical entity that is commonly encountered in clinical practice of chronic pain. Foraminal or central stenosis due to herniated discs, osteophytes and consequent mechanical pressure/biochemical changes involving dorsal nerve roots are thought to be common etiologies. However, the precise pathophysiology that underlies this pain state is not yet known. Current therapies with some efficacy include pharmacologic approaches primarily with neuropathic pain medications and interventional therapies, such as epidural steroid injections, spinal cord stimulation, and highly invasive therapies, such as cervical vertebral fusion.
Despite these available modalities, the long-term success in alleviating radicular neck pain is limited and there is a great need for newer and sustainable therapies. In addition, there is also a growing and palpable concern regarding catastrophic complications with cervical epidural steroid injections and the lack of efficacy with fusion surgery.
In view of the lack of a ‘cure’ for chronic radicular neck pain, efficacy is currently measured with amount and duration of pain relief. Any modality that relieves pain quantitatively more and chronologically longer, with a similar or better side-effect profile than existing therapies is certainly desirable. Despite the aforementioned methodological limitations, van Zundert and colleagues’ article, describing short-term efficacy of PRF adjacent to the DRG in selected patients, is an optimistic step towards experimenting with testing new modalities of treatment for chronic radicular neck pain Citation[1].
Although the precise analgesic mechanism of PRF is not yet completely established, the relative safety and efficacy of this procedure to treat chronic cervical radicular pain appears promising. Specific patient selection criteria, technical improvements, economic considerations and protocols for frequency of treatment administration are a few of the important issues that will need to be addressed (hopefully through more randomized controlled trials) before PRF can be recommended for mainstream application. It should be noted that conventional cervical RF has not been shown to definitively provide long-term pain relief and newer therapies have no optimal ‘gold standards’ to compare their efficacy against.
It will be interesting to see a prospective, randomized crossover study comparing pulsed RF and cervical epidural steroid injections in the future.
In summary, treatment of chronic cervical radicular pain with PRF is a novel application. Although more studies are needed to support its routine use, one can argue that this randomized, double-blinded trial provides better quality evidence than existing studies for use of epidural steroid injections for cervical radicular pain. In addition, the PRF may have a more advantageous risk–benefit ratio.
References
- van Zundert J, Patijn J, Kessels A et al. Pulse radiofrequency adjacent to the cervical dorsal root ganglion in chronic cervical radicular pain: a double blind sham controlled randomized clinical trial. Pain127, 173–182 (2007).
- van Zundert J, Lame IE, de Louw A et al. Percuaneous pulsed radiofrequency treatment of the cervical dorsal root ganglion in the treatment of chronic cervical pain syndromes: a clinical audit. Neuromodulation6, 6–14 (2003).
- van Kleef M, Liem L, Lousberg R et al. Radiofrequency lesion adjacent to the dorsal root ganglion for cervicobrachial pain: a prospective double blind randomized study. Neurosurgery38, 1127–1131 (1996).
- Slappendel R, Crul BJ, Braak GJ et al. The efficacy of radiofrequency lesioning of the cervical spinal dorsal root ganglion in a double blinded randomized study: no difference between 40°C and 67°C treatments. Pain73, 159–163 (1997).